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QBlade Guidelines v0.6

1. Figure 3 9 VAWT rotor simulation submodule N O1 3 TUTORIAL How to create simulations in QBlade press the Rotor DMS Simulation button second green button press Define Rotor Simulation enter the simulation parameters and select corrections see the groupbox in the top right corner of Fig 3 9 enter a tipspeed ratio range from 1 to 10 and an increment of 0 5 press Start DMS explore the created simulation data by changing plot variables and graph types change the tipspeed ratio and height position in the upper dropdown menus create another rotor simulation for the same rotor but with different sim ulation parameters and compare the results for example by isolating and comparing local curves create another rotor simulate it and compare the results 25 File View Blade 360Polar Turbine Options Turbine Turbine Simulation Windspeed m s Height Position a x VAWT Simulation Parameters P Ww h Simulation Parameters Turbine Data 120 TA 7 Tip Loss Rho 1 2041 Transmission V Cut In Viscosity 1 78000000e 05 V Cut Out _ Var Interference Factors Elements 50 Rotational Speed max Iterations 1000 IM Epsilon 0 0010 Relax Factor 0 3 Turbine Blade New VAWT Blade f i Windprofile pow Turbine Offset 1 00 m bel Soi Turbine Height 1 00 m Rotor Height 1 00 m Rotor Max Radius 0 60 m Wind j From Rotor Swept Area 5333 33 cm i VariableLosses 0 000 s Windspeed To
2. Figure 3 8 VAWT blade design and optimization submodule press the VAWT Rotorblade Design button first green button press New Blade 3 8 or configure your own blade press Save configure the Darrieus rotor using the Scale and Optimize options see Fig 23 In a DMS simulation an additional graph type is available the azimuthal graph As the flight path of a VAWT blade is a circle around its rotational axis the rela tive speed at the blade is not only dependent on the blade element height posi tion but also on the blade position on this flight path 24 mm QBlade v0 6 on XFLRS v6 06 ba ba e File View Blade 360 Polar Turbine Options INVERSE j a R e ANS Hw LL d ANIE Rotor Blade Rotor Simulation Tip Speed Ratio Height Position mang LEE 9 i New VAWT Blade y New VAWT Blade Simulation 5 00 gt 0 024 M VAWT Simulation Parameters Bmx hH Simulation Parameters Fl Tip Loss Rho 1 2041 0 8 Viscosity 1 78000000e 05 0 6 Var Interference Factors Elements 50 max Iterations 1000 0 4 Epsilon 0 0010 Relax Factor 0 3 0 2 Windprofile const 0 0 4 Analysis Settings RU 0 2 Define Rotor Simulation Lambda Start 0 4 139 Lambda End 10 00 0 6 Lambda Delta 0 50 0 8 Start DMS Graph Curve Settings Y Curve E Points Y Selected Op Point Style New VAWI Blade Cp Width New VAWT Blade Simulation 0 7 Color 0 6 0 5 0 4 0 3 0 2 0 1 0 0 0 0
3. v Straight Rotor Simulation gt 4 00 0 001 0 0 0 2 0 4 0 6 0 05 0 8 Straight Rotor Straight Rotor Simulation h H 0 0 0 6 VAWT Simulation Parameters Simulation Parameters Analysis Settings f Rho 1 2041 H Viscosity 1 78000000e 05 actors Elements 50 max Iterations 1000 Epsilon 0 0010 Relax Factor 0 3 Windprofile const Define Rotor Simulation Lambda Start Lambda End Lambda Delta 5 00 0 50 Start DMS Graph Curve Settings 4 Curve Style Width Color Figure 7 7 The rotor simulation submodule Points y Selected Op Point In the rotor simulation submodule the user can commit rotor blade simulations over a range of tipspeed ratios A rotor simulation can only be defined when at least one rotor blade is present in the runtime database When defining a rotor simulation the user has to select the desired corrections to the DMS algorithm and the simulation parameters Once a simulation is defined the user can select a range of A values tipspeed ratios and the incremental step for the simulation A rotor simulation is always dimensionless The freestream velocity is assumed to be unity and the rotor radius and height are normalized for the computation This implies that no power curve or load curves can be computed during a rotor simulation 64 7 The OBlade VAWT Module 7 4 The turbine definition and simulation su
4. and an increment of 1 and press XDirect Analysis settings 9 a c V Sequence Start 5 00 deg End 25 00 deg de 0 50 deg V Viscous Init BL V Store Opp Analyze Polar properties Type 0 Fixed speed Reynolds number 1000000 Mach number 0 00 NCrit 9 00 Forced top trans 1 00 Forced bottom trans 1 00 Number of data points 61 Graph Curve Settings 4 Curve Points Style Width Color Y press the XFOIL Direct Design button cM third red button 3 TUTORIAL How to create simulations in OBlade To simulate a wind turbine the AoA range of the polar needs to be extrapolated to 360 this is done in the polar extrapolation module Only extrapolated polar data can be used to simulate a turbine or rotor The sliders on the left side of Fig 3 4 can be used to better match the extrapolation with the previously computed polar data Below the sliders a value for Cp oo can be specified When the ex trapolated polar is saved it is stored in the runtime database Additionally it is possible to load a cylindrical foil and its 360 polar This foil has zero lift and a drag value that can be specified by the user Such cylindrical foils are used in the root region of a HAWT blade for structural reasons QBlade v0 6 on XFLR5 v6 06 File View Blade 360Polar Turbine Options 2 Rm ANNAN fr A Airfoils Polars 8 nl NACA 5518 y TO Re1 000 M0 00 N9 0 HAWT NACA 5518 360 Polar M C
5. Delete section 10 Pos m Chord m Twist in deg Foil Polar ia 1 0 00 2 19 12 00 circle circle 360 Polar 2 1 50 219 12 00 circle circle 360 Polar 3 3 50 249 12 00 TRANSIT TRANSIT 360 Polar 4 6 50 3 09 12 00 TRANSIT TRANSIT 360 Polar 5 8 00 3 20 11 001 DU 00 W 401 DU 00 W 401 360 Polar 6 11 00 343 8 87 DU 00 W 350 DU 00 W 350 360 Polar 7 14 00 2 97 7 24 DU 97 W 300 DU 97 W 300 360 Polar 8 17 00 2 18 5 92 DU 91 W2 250 DU 91 W2 250 360 Polar 9 20 00 2 53 4 2 NACA 63 4 421 NACA 63 4 421 360 Polar 23 00 2 29 3 64 NACA 63 4 421 NACA 63 4 421 360 Polar 11 26 00 2 07 2 71 NACA 63 4 421 NACA 63 4 421 360 Polar 12 29 00 1 86 1 98 NACA 63 3 418 NACA 63 3 418 360 Polar 13 32 00 1 64 1 41 NACA 63 3 418 NACA 63 3 418 360 Polar 14 35 00 141 0 91 NACA 63 3 418 NACA 63 3 418 360 Polar 15 38 00 1 22 0 47 NACA 63 3 418 NACA 63 3 418 360 Polar 16 41 00 0 99 0 04 NACA 63 3 418 NACA 63 3 418 360 Polar Modify Shape Scale Pitch Blade 0 00 Optimize C m C anedon se teta NACA 63 3 418 NACA 63 3 418 NACA 63 3 418 44 450 m NACA 63 3 418 42 200 m NACA 63 3 418 39 200 m NACA 63 3 418 36 200 m NACA 63 4 421 33 200 m NACA 63 4 421 30 200 m NACA 63 4 421 27 200 m DU 91 02 250 24 200 m DU 27 W 300 21 200 m DU 00 W 350 18 200 m DU 00 W 401 15 200 m TRANSIT 12 200 m TRANSIT circle 9 200 m circle 7 700 m 4 700 m 2 700 m 1 200 m screenshots Figure 6 2 Blade d
6. circulation T 4C V 4c m 5 55 7 The QBlade VAWT Module 7 1 Basics There are many different types and shapes of wind turbines Those with a ver tical axis of rotation are called Vertical Axis Wind Turbines VAWT OBlade in cludes a module for the simulation of those wind turbines The implemented algorithm is applicable for the performance analysis of lift based VAWT s such as the classical Eggbeater Darrieus rotor Based on the calculated airfoils po lars and 360 polars the blade shape is defined in the blade design submodule This part of the program provides a range of scaling and optimization functions as well In the following the user can choose between rotor simulation and turbine simulation The former one is a dimensionless calculation for a range of tip speed ratios whereas the latter one requires the definition of concrete turbine parameters such as rpm and is executed for a range of windspeeds In either module simulation parameters and corrections can be selected for the calcula tion For visualization purposes three different graph types are available to plot the simulation data the blade graph for vertical plots the azimuthal graph for circumferential plots and the rotor graph for plots of global variables such as the power coefficient 7 1 1 Method of operation The cross section of a VAWT blade is an airfoil producing lift and drag that drive the wind turbine The force on a blade section depends on both t
7. 00 0 25 9 20 00 0 00 0 00 0 25 10 23 00 0 00 0 00 0 25 11 26 00 0 00 0 00 0 25 12 29 00 0 00 0 00 0 25 13 32 00 0 00 0 00 0 25 14 35 00 0 00 0 00 0 25 15 38 00 0 00 0 00 0 25 16 41 00 0 00 0 00 0 25 17 42 00 0 00 0 00 0 25 18 42 80 0 00 0 00 0 25 4 m Back 7 Orthogonal Sections screenshots Figure 6 7 Advanced design window The advanced design module enables the user to define the blade shape in more detail Offset specifies an offset of the airfoil section in x direction Dihedral defines the angle between the blade chord and the y axis Thread axis X and Z specify the point on the selected airfoils surface around which it is twisted However the changes applied on a blade in the advanced design module dont affect the blades performance in a BEM simulation This is because the BEM doesnt account for the full 3D shape of a blade However the geometry of the 3D blade can be exported as an st file Future implementations planned for QBlade will make use of the full 3D description of the blade 38 6 The OBlade HAWT module 6 3 The rotor simulation submodule QBlade v0 6 on XFLR5 v6 06 File View Blade 360 Polar Turbine Options Re ANUN LE Rotor Blade Rotor Simulation Tip Speed Ratio mung 9 ti s88v3 v S88V3 Simulation 1 00 HAWT Simulation Parameters B Simulation Parameters Rho 1 2000 Viscosity 1 77999991e 05 Elements 100 max Iterations 1000 Epsilon 0 0001 Correctio
8. 006 2006 7 GLAUERT Hermann Airplane Propellers In DURAND William F Aero dynamic theory 4 Springer Berlin 1935 8 MAHERI A NOROOZI S TOOMER C VONNEY J Damping the fluctu ating behavior and improving the convergence rate of the axial induction factor in the BEMT based aerodynamic codes University of West England BS16 1C Pristol 2006 9 MIKKELSEN R Actuator Disk Methods Applied to Wind Turbines Dissertation MEK FM PHD 2003 02 Technical University of Denmark 2003 10 MONTGOMERIE B Methods for Root Effects Tip Effects and Extending the An ele of Attack Range to 100deg with Application to Aerodynamics for Blades on Wind Turbines and Propellers FOI Swedish Defence Research Agency Scien tific Report FOI R 1035 SE 2004 11 VITERNA L A CORRIGAN R D Fixed Pitch Rotor Performance of Large Hor 75 Bibliography izontal Axis Wind Turbines NASA Lewis Research Center Cleveland Ohio 1982 12 PECHLIVANOGLOU G The Effect of Distributed Roughness on the Power Per formance of Wind Turbines GT2010 23512 Berlin University of Technology Berlin 2010 13 SHEN W Z MIKKELSEN R SORENSEN J N BAK C Tip Loss Corrections for Wind Turbine Computations Wind Energy 2005 Wiley 2005 14 TANGLER J The Nebulous Art of using Wind Tunnel Airfoil Data for Predicting Rotor Performance NREL CP 500 31243 National Renewable Energy Labo ratory Golden Colorado 2002 15 BLACKWEL
9. 5 00 10 TN Power Regulation Pitch E Transmission Single New Tip Loss Viscosity 1 78000000e 05 Pitch from Power 2000 00 W 5 00 104 Root Loss Elements 50 V Cut In 1 00 m s New Root Loss max Iterations 1000 V Cut Out 18 00 m s ER 3D Correction 0 0010 1 00 10 Rotational Speed 200 00 rpm Foil Interpolation 3 00 10 Turbine Blade New HAWT Blade Outer Radius 10 20 m loss Fixed Pitch 0 00 10 00 mjs VariableLosses 0 000 z Fixed Losses 0 00 W Loo 104 20 00 m s Create Edit Delete Turbine 2 00 m s V m s V m s Create i 0 00 100 10 0 12 0 14 0 16 0 18 0 0 0 5 0 100 15 0 Weibull Settings k 9 00 A 2 00 New Turbine a_a New Turbine Simulation 1 2 1 0 0 8 0 6 0 4 0 2 s m 0 0 0 0 2 0 40 6 0 8 0 10 0 Annual Yield 0 Wh Figure 3 7 HAWT turbine definition and simulation submodule 21 b 10 11 125 22 DT A er press the Turbine BEM Simulation button fourth blue button press Create to create a turbine enter the turbine data see the groupbox on the left side of Fig 3 7 press Save press Define Turbine Simulation enter the simulation parameters and select corrections see the groupbox in the top right corner of Fig 3 7 enter a windspeed range from 1 to 18 s and an increment of 0 5 s press Start BEM explore the created simulation data by changing plot variables and graph types change the k and A parameters of the Weibull distribution to inv
10. ANNAN ee L Airfoils 1 E NACA 5518 y TO Re1 000 M0 00 N9 0 HAWT NACA 5518 360 Polar M Create 360 Polar Save 360 Polar Alpha deg CD90 1 80 AR v Compare 360 Polars Style Width Color Figure 5 1 The 360 polar extrapolation submodule 5 0 2 Montgomery extrapolation For the Montgomery extrapolation procedure basic lift and drag curves are needed It is then assumed that the flow around the airfoil can be treated as potential flow near 0 and 180 AoA At other AoA s the flow approximately behaves like for a stalled thin plate A blending function is used in the transi tion region between the potential flow straight line and the flat plate curve The user can take influence on the apexes of the resulting coefficient curves via different sliders The two points C and Cr from which the blending function f for the positive extrapolation is constructed can be manipulated using the sliders A for CL1 and B for C 5 The sliders A and B manipulate the corre sponding points for the negative extrapolation Additionally a favored 2D drag coefficient Cp 99 at 90 AoA can be selected manually as well Whenever a slider 31 is moved or the value for Cp 99 is changed the whole extrapolation is computed again With the option edit current polar the currently selected 360 polar can be edited manually after it has been extrapolated The Montgomery extrapolation is carried
11. Turbine E New Turbine Simulation Width 0 7 pitch Color pitch Simulation screenshots Figure 6 10 The turbine definition and simulation submodule 6 5 The turbine definition and simulation submodule In the turbine definition and simulation submodule the user can define a wind turbine To define a wind turbine a rotor blade must be present in the runtime database To create a turbine the turbine type and the turbine parameters have to be specified The turbine type is defined by e Regulation pitch or stall e Transmission single 2 step or variable If a pitch regulated turbine is defined the user has to specify a nominal power output When the windspeed that yields the nominal power output is reached 41 6 5 The turbine definition and simulation submodule the blades are pitched to reduce the power for higher windspeeds to the nominal output A stall regulated turbine has no pitch control and the power output is limited solely when stall occurs at the rotor Designing a stall turbine that limits its power to the desired output and at the desired windspeed requires an iterative approach For a single speed transmission the user has to select only one rotational speed in which the turbine operates over the whole range of windspeeds For 2 step transmission two rotational speeds and a windspeed at which the transmission switches have to be selected A variable transmission turbine has a minimum and a maximum value for t
12. Variable listings As stated before all the variables calculated in a rotor simulation are dimension less 1 global e power coefficient Cp e thrust coefficient CT e tipspeed ratio A e power coefficient based on tipspeed Kp Ep e inverse tipspeed ratio 2 local axial induction factor a radial induction factor a local tipspeed ratio Aoc radial position r dimensionless normal force component Cy dimensionless tangential force component C inflow angle 9 relative angle twist angle 0 chord c lift coefficient Cr drag coefficient Cp 53 6 7 Simulation results e lift to drag Ratio EL e PRANDTL tiploss factor F e number of iterations n e annulus averaged axial induction factor e annulus averaged radial induction factor In a turbine simulation the following variables are computed additionally to the variables resulting from a rotor simulation 1 global e power P W e thrust TIN windspeed Vj m s angular speed c rpm pitch angle WEIBULL probability hw WEIBULL probability windspeed hw V m 53 root bending moment M Nm e power coefficient including losses Cp Joss 2 local e local REYNOLDS number Rej ATP e Re deviation from polar simulation Rejo Repolar e critical roughness Keritical 100 7 mm from 12 e resultant velocity V m s 54 6 The OBlade HAWT module tangential force per length Pr N m normal force per length Py N m Mach number Ma
13. by the Sandia National Laboratories is implemented as well To find a fitting arc radius for a certain troposkien shape the user has to define a start and end radius as well as a step size The best radius is calculated on the basis of the smallest maximum distance between Troposkien and Sandia shape 7 The OBlade VAWT Module Optimize VAWT Blade Geometry From Position 1 w to Position Optimize Blade Radius 5 None 5 Straight Blade Helix Blade R Circ Angle Start Circ Angle End Troposkien 8 Arc Straight Line R max 0 28 R arc start 0 10 R arc end 0 90 dR 0 01 Done Figure 7 5 Blade optimization dialog 7 2 2 Blade scaling The following scaling functionalities speed up the rotor modification e height scaling change the overall rotor height height shifting vertically shift whole rotor without changing it e chord scaling scales the chord length radius scaling scales the radial position e twist scaling sets a constant twist angle Scale VAWT Blade Dig Reference Height Scaling 0 562 Height Shifting 0 000 Chord Scaling 0 015 Radius Scaling 0 220 Twist Scaling 0 00 Figure 7 6 Blade scaling dialog 63 7 3 The rotor simulation submodule 7 3 The rotor simulation submodule pm QBlade v0 6 on XFLR5 v6 06 File View Blade 360Polar Turbine Options R e ANNS LL Rotor Blade Rotor Simulation LJ Tip Speed Ratio Height Position e e Straight Rotor
14. dialog e fluid density p e fluid viscosity v e number of blade elements N e maximum number of iterations e maximum e for convergence e relaxation factor Wrelax Density The density of the fluid around the wind turbine is needed to calculate the power output 1 P PAV Cp 6 12 The density is only used to compute the power output for a turbine simulation During a rotor simulation all variables are dimensionless and only depend on the tipspeed ratio 44 6 The OBlade HAWT module Dynamic viscosity The dynamic viscosity is needed to compute the local REYNOLDS number along the blade Re r ee 6 13 The dynamic viscosity is only used to compute the REYNOLDS number during a turbine simulation During a rotor simulation all variables are dimensionless and only depend on the tipspeed ratio Number of elements The number of elements specifies into how many elements the blade is divided This number is independent from the number of blade sections The BEM al gorithm is executed once for every element The input values like chord and twist are interpolated between the blade stations where they are defined and computed for the centers of the elements The elements are distributed using sinusoidal spacing This allows for more elements to be placed in the tip and root region where largest gradients usually are to be expected By using sinu soidal spacing the overall number of elements that are required
15. is less and the computational time is reduced Element Center Figure 6 13 Sinusoidal spaced elements along the blade All the variables resulting from the BEM simulation are computed for the center of an element and are treated as the averaged values over an element This solves a problem that arises if the values would be computed for the boundaries of an element and then interpolated to the center from there When the PRANDTL tip loss factor F goes to zero at the tip or at the hub numerical instabilities arise and result in a non converging iteration This problem is skipped because the center of an element can be arbitrarily close to the tip or hub of the blade but never be on the same position it is always oi away A is the width of the i element 45 6 6 Simulation settings The forces per length Py and Pr that were computed for the element center are integrated over the whole element to yield the element s contribution to the total torque and thrust Convergence criterion The convergence criterion e defines when an iteration has converged The max imum of the difference of axial and radial induction factor between the last and the current iteration has to be below e for convergence A recommendation is e 107 nax a agg a au lt 6 14 Maximum number of iterations The maximum number of iterations prevents that the algorithm may get stuck in an infinite loop Relaxation factor A common prob
16. out as described in Methods for Root Ef fects Tip Effects and Extending the Angle of Attack Range to 100 with Application to Aerodynamics for Blades on Wind Turbines and Propellers 10 5 0 3 Viterna Corrigan post stall model The Viterna approach to extending the polar data to all possible angles of at tack consists of empirical equations It is an idealized model which results in an approximately constant power output after stall provided that the blade expe riences high windspeeds It is also based on the aspect ratio of the future wing which can be modified by the user As the extrapolation depends on the AR value blades with different aspect ratios require separate 360 polars When ever the aspect ratio is changed the whole extrapolation is computed again The Viterna extrapolation is carried out as described in Fixed Pitch Rotor Perfor mance of Large Horizontal Axis Wind Turbines 11 32 6 The QBlade HAWT module 6 1 Basics 6 1 1 The Blade Element Momentum Method The classical Blade Element Momentum BEM theory couples the momentum theory or disk actuator theory a mathematical model of an ideal actuator disc with the blade element theory which describes the local events taking place at the actual blade The blade is discretized into a finite number of blade elements Two sections bound an element that sweeps the rotor plane on a circular path The blade cross sections are defined by their radial position profi
17. 0 polar object is created in the 360 polar extrapolation submodule It is defined by a name and a parent polar the original XFOIL polar that was ex trapolated The lift and drag coefficients over the whole 360 range of the AoA are stored as data If the parent polar is deleted the extrapolated polar will be deleted as well to ensure consistency If a 360 polar object is deleted all blades turbines and simulations utilizing it are deleted too Blade object A blade object is created in the blade design and optimization submodule It stores the geometric blade data chord radial position twist offset etc of the 10 2 Software implementation specified blade sections and the associated foils and 360 polars It is defined by a name If a blade object is deleted all associated simulations and turbines are deleted as well Turbine object A turbine object is created in the turbine definition submodule It stores all tur bine parameters pitch stall single variable 2 step transmission etc and the associated rotor blade If a turbine object is deleted all associated simulations are deleted as well Simulation object A rotor or turbine simulation object is created when the respective simulation is defined It memorizes the simulation parameters max iterations elements epsilon and corrections tiploss etc and during a simulation stores the global results characterizing the whole rotor A Cp Cr etc If a si
18. 18 00 m s Fixed Losses 0 00 W Windspeed Delta 0 50 m s 1 00 m s Create Edit Delete Turbine 0 0 0 2 0 4 0 6 9 00 New Turbine F x Tot N e New Turbine Simulation Annual Yield 521489 Wh Figure 3 10 VAWT turbine definition and simulation submodule 26 CO N 10 11 I2 13 Nok DNA 3 TUTORIAL How to create simulations in OBlade press the Turbine DMS Simulation button 1 third green button press Create to create a turbine enter the turbine data see the groupbox on the left side of Fig 3 10 press Save press Define Turbine Simulation enter the simulation parameters and select corrections see the groupbox in the top right corner of Fig 3 10 enter a windspeed range from 1 to 18m s and an increment of 0 5m s press Start DMS explore the created simulation data by changing plot variables and graph types change the tipspeed ratio and height position in the upper dropdown menus change the k and A parameters of the Weibull distribution to investigate the annual yield create another turbine simulation for the same turbine but with different simulation parameters and compare the results for example by isolating and comparing local curves create another turbine simulate it and compare the results 27 Via the File menu or the main toolbar the user can save the whole project in cluding foils polars blades and simulations as a wpa file 1 click File
19. 5 Variable Loss 1 40 106 1 20 106 1 00 106 8 00 10 6 00 10 4 00102 2 00 1092 0 00 100 0 10 20 30 Figure 6 11 Different variable loss factors and their effect on power output speed to occur is hy Vo i X ep amp 6 9 The probability f V lt Vo lt Vj 4 that a windspeed lies between V and Vj f Vi Vo Vii exp 3 exp Ea 3 6 10 Thus the annual energy production is calculated as N 1 AEP Y 5 P Visa P V f Vi lt Vo lt Visa 8760 611 1 1 A turbine simulation is carried out over a range of windspeeds with the chosen incremental step size Depending on the specified rotational speed of the tur bine a tipspeed ratio is computed for every windspeed Then a BEM simulation over the computed tipspeeds that is equivalent to a rotor simulation is carried out 6 6 Simulation settings 6 6 1 Simulation Parameters When defining a simulation the following parameters have to be set 43 6 6 Simulation settings je Define BEM Parameters Simulation Name New Turbine Simulation Corrections Variables E Prandti Tip Loss Y New Tip Loss E Prandtl Root Loss W New Root Loss E 3D Correction 4 Reynolds Drag Correction 4 Foil Interpolation 50 00 0 001 1000 00 0 35 1 8e 05 Discretize Blade into N Elements Max Epsilon for Convergence Max Mumber of Iterations Relax Factor Rho Viscosity Figure 6 12 Simulation definition
20. 6 15 Damped fluctuation of the axial induction factor for different relax ation factors 8 applied to let the first few oscillations happen These oscillations then mark the boundary of the neighborhood of the final result With a three point equation the axial induction factor is then placed inside this neighborhood 1 1 1 Ak 1 qe udi gik 6 16 From there the iteration proceeds as normal with the desired relaxation factor and eq 6 15 applied 6 6 2 Corrections Due to the two dimensional nature of the BEM theory three dimensional effects can not be accounted for by the classical BEM This leads to large deviations of the computed data compared with measured turbine data especially under the influence of stall The three dimensional effects responsible for this are 47 6 6 Simulation settings 0 562 7 0 560 0 558 0 556 A A A A A Axial induction factor 0 552 0 550 Iteration 0 548 va 0 1 2 3 4 5 6 7 8 9 10 t Ex 1 with RF 21 No relaxation e Eq 1 with RF 0 5 for all K s A Eq 1 with RF 1for K 1 and RF 0 5 for k gt 1 EH Eq 1 with RF 1for K lt 3 Eq 2 for K 3 Eq 1 with RF 1 for k gt 3 Figure 6 16 Accelerated convergence by placing the induction factor inside the neighborhood of the final result 8 e The wind velocity in the rotor plane is assumed to be co
21. L B F The Vertical Axis Wind Turbine How It Works SLA 74 0160 Sandia Laboratories Albuquerque New Mexico April 1974 16 PARASCHIVOIU I Wind Turbine Design With Emphasis on Darrieus Concept Presses Internationales Polytechnique Canada 2002 17 SNEL H HOUWKING R VAN BUSSEL G J W BRUINING A Sectional Pre diction of 3D Effects for Stalled Flow on Rotating Blades and Comparison with Measurements Proc European Community Wind Energy Conference H 5 Stevens and Associates LA beck Travem 1nde 1993 18 HERNANDEZ J CRESPO A Aerodynamics Calculation of the Performance of Horizontal Axis Wind Turbines and Comparison with Experimental Results Wind Eng 11 4 pp 177 187 1987 19 ZHANG J H Numerical modeling of a vertical axis wind turbine VAWT MEK FM EP 2004 11 Technical University of Denmark 2004 20 FUGLSANG P ANTONIOU I SORENSEN N MADSEN H A Validation of a wind tunnel testing facility for blade surface pressure measurements Riso National Laboratory Denmark 1998 76
22. Points Centerline Style 1 Spline foil 9 03 31 20 0 00 50 90 60 0 00 0 00 0 00 v 2 NACA 5518 18 00 2910 5 00 50 70 99 0 00 0 00 0 00 Y Figure 3 2 Airfoil Design module 1 press the Airfoil Design button first red button 2 click Foil gt Naca Foils 3 enter 5518 in the 4 or 5 digits line edit 4 press OK 15 In the XFOIL Direct Analysis module the flow around the airfoils is simulated to create a polar An analysis can be defined under the menu point Polars then the simulation can be started The analysis will only converge for a limited range of AoA values typically from about 5 AoA to 25 AoA It is also possible to import polar data in this module for instance to utilize experimental data Please note that whenever polar data is imported an arbitrary airfoil with exactly the same name as the imported polar data needs to be created to connect the polar data with this airfoil b QBlade v0 6 on XFLR5 v6 06 File View Foil Design Analysis Polars Operating Points Options Re AA ZU In C NACA 5518 y TO_Re1 000_M0 00_N9 0 v 25 00 Xtri 0 0 0 0 0 2 20 4 0 6 NACA 5518 TO Re1 000 M0 00 N9 0 Figure 3 3 XFOIL Direct Analysis module click Analysis gt Define an Analysis E Durum Analyze 16 enter 1000000 in the Reynolds line edit and press OK check the Sequence checkbox in the Analysis Settings on the right enter an AoA range from 5 to 25
23. TT gt QBlade Guidelines P C v0 6 David Marten Juliane Wendler January 18 2013 Contact david marten at tu berlin de Contents 1 Introduction 5 1 1 Blade design and simulation in the wind turbine industry 5 12 The sotwate projec a e perigee oun oh oR 7 2 Software implementation 9 2 Code Hmitaliotisa eae ea Bae dae Hoe he A a 9 22 COGe Structure a oa eus ees 9 23 Plotting results Graphcontrols 11 3 TUTORIAL How to create simulations in QBlade 13 4 XFOIL and XFLR QFLR 29 5 The QBlade 360 extrapolation module 30 LOL BASCS dea ioi amp o dp Pelrus dao Geib ae Pob Hed ws ed as 30 5 0 2 Montgomery extrapolation o o 31 5 0 3 Viterna Corrigan post stall model 32 6 The QBlade HAWT module 33 EID DTP 33 6 1 1 The Blade Element Momentum Method 33 6 12 eration procedure uy irte oe pandas 33 6 2 The blade design and optimization submodule 34 62 1 Blade opUrnizaloll ree dedi edt etes 36 622 Dlade Scal sra presse 37 6 2 5 Advanced UEST 4 s x ossi wd yox mE Rma 38 63 The rotor simulation submodule 39 6 4 The multi parameter simulation submodule 40 6 5 The turbine definition and simulation submodule 41 6 6 Simulation Seltngs sigd 4 6 2 42 ci ia a LER ME i 43 6 6 1 Simulation Parameters 43 OO WODEIBCHOLIS e g a oo ee ee 47 6 7 Sumulation Testi e uu e ee
24. a values The curve belonging to the currently selected lambda value in the right drop down menu is highlighted In the graph s context menu the user may iso late the highlighted curve and then compare it to the local curves of other rotor simulations at the same tipspeed ratio If multiple rotor simulations are stored in the database the curves of global variables are always shown simultaneously inarotor graph mm QBlade v0 6 on XFLR5 v6 06 o Jes File View Blade 360Polar Turbine Options INVERSE 360 A A x Fi AAA A ai ANJI y Rotor Blade Rotor Simulation Tip Speed Ratio 1 2 9 ti New HAWT Blade v New HAWT Blade Simulation 6 50 M HAWT Simulation Parameters mx gt e Simulation Parameters T Rho 1 2041 Viscosity 1 78000000e 05 0 40 14 Root Loss Elements 50 max Iterations 1000 0 35 12 3D Correction Epsilon 0 0010 0 30 Reynolds Drag Correction RelaxFactor 0 3 1 0 0 25 0 8 Analysis Setti 0 20 ings 0 6 Define Rotor Simulation 0 15 Tip Speed Ratio Start 1 00 0 4 0 10 Tip Speed Ratio End 17 00 0 05 0 2 Tip Speed Ratio Delta 0 50 TSR TSR 0 00 0 0 Start BEM 0 0 5 0 10 0 15 0 0 0 5 0 10 0 15 0 Graph Curve Settings 4 Curve Points Y Selected Op Point New HAWT Blade aa 3 New HAWT Blade Simulation Width N Color Figure 3 6 HAWT rotor simulation submodule 19 20 N e O1 A press the Rotor BEM Simulation button sec
25. ariable and a parameter for each individual graph For the currently selected main variable and parameter the resulting series of curves is displayed in each graph When the selected windspeed rotational speed or pitch angle is changed in the top toolbar the series of curves is changed accordingly This submodule is of great help when designing custom control strategies for variable rotational speed and or pitch controlled wind turbine rotors im QBlade v0 6 on XFLR5 v6 06 eJ File View Blade 360Polar Turbine Options Ara eL 4 1 Rotor Blade Multi Parameter BEM Simulation Windspeed m s Rotational Speed 1 min Pitch deg ques 9 t New VAWT Blade v MEXICO 1 5m radius free transition RE 250 000 Simul v 4 00 y 260 00 y 2 00 M HAWT Simulation Parameters Bx p PM Simulation Parameters Rho 1 2000 3 00 103 Viscosity 1 77999991e 05 7 00 103 T asd 2 5 00 103 max Iterations 1000 5 00 103 3D Correction Epsilon 0 0010 ag Correction Relax Factor 0 3 4 00 103 3 00 103 Characteristic Simulation Parameters 2 00 103 Define Characteristic Simulation 1 00 103 Wind Speed Range 3 00 100 Start 1 00 m s 7 Fix b amp 1 00 103 End 20 00 m s Delta 0 50 m s Rotational Speed Range T Nm PI y pl Start 20 00 1 min E Fix 180 fii End 50 00 1 min 160 Delta 5 00 t min 140 Pitch Range 120 Start 0 00 deg Fix 100 End 10 00 deg 80 Delta 1 00 deg Start Charact
26. as to be available to ensure the continuation of the BEM and DMS algorithms The lift and drag coefficients consequently have to be extrapolated for the whole 360 range of the AoA In general experimental pre stall data a 15 is available for common airfoils and XFOIL is suitable to generate such data as well For post stall data on the other hand some further considerations are needed With increasing AoA the frontal area facing the airflow increases too Stall occurs the foil dramatically stops producing lift and the drag coefficient increases Around 180 the trailing edge of the streamlined airfoil faces the flow resulting in decreasing drag and higher lift again Hence the flow characteristics evolve from those of a thin streamlined airfoil to those of a blunt body and back during a 180 revolution of the blade Polars that are either imported or a result of an XFOIL analysis can be extrap olated to the full 360 AoA range in the 360 polar extrapolation submodule A polar can be selected from the drop down menu in the toolbar When creat ing an extrapolation the user can choose between two extrapolation algorithms firstly the sophisticated Montgomery extrapolation can be chosen Secondly the Viterna Corrigan post stall model which is favored in industrial environments is disponible too 30 5 The OBlade 360 extrapolation module QBlade v0 6 on XFLR5 v6 06 File View Blade 360Polar Turbine Options R
27. blade a Qp 0 6 4 where 0 0 B is a combination of the twist angle B and the pitch angle 0 Now the lift and drag coefficients of the airfoil can be obtained from a table and the lift and drag caused by the airfoil can be calculated From these forces new induction factors can be computed and compared to the initial induction factors If max Aa Aa is below the convergence criterion e the iteration has converged and the next annular element can be computed 6 2 The blade design and optimization submodule In the blade design and optimization sub module the user can create a rotor blade A blade consists of an arbitrary number of sections see Fig 6 3 Every section is defined by position chord twist airfoil and the associated 360 polar A new blade can only be created when there is at least one 360 polar object present in the runtime database and it can only be saved when a foil and a polar is selected at every station The number of blades of the future rotor has to be 34 6 The OBlade HAWT module m pm QBlade v0 6 on XFLR5 v6 06 File View Blade 360 Polar Turbine Options Rotor Blade LI S88V3 HAWT 3D View Control Show E Turbine J Surfaces Perspective Projection Axes MEE sesv3 Number of Blades 3 Hub Radius x ox AA rr LA 1 20 m Y Blade Coordinates Insert before section i0 Insertafter section i0
28. bmodule QBlade v0 6 on XFLR5 v6 06 File View Blade INVERSE 2 e AAA m Turbine Simulation Turbine L 360 Polar Turbine Options AMET Windspeed m s 9 i i Darrieus Turbine v Darrieus Turbine Simulation VAWT Bx Turbine Data Transmission Single V Cut In 0 00 m s V Cut Out 20 00 m s Rotational Speed 500 00 rpm Turbine Blade Darrieus Rotor Turbine Offset 0 00 m Turbine Height 0 56 m Rotor Height 0 56 m Rotor Max Radius 0 25 m Rotor Swept Area 0 19 m VariableLosses 0 100 Fixed Losses 0 00 W Create Edit Delete Turbine Create Edit Weibull Settings k 2 00 A 9 00 Annual Yield 0 Wh V m s P Iw 00 0 00 0 02 0 04 0 06 0 08 0 10 A PA Height Position h 10 00 10 4 8 00 10 4 6 00 10 4 4 00 1074 2 00 10 4 u up 0 00 100 0 00 0 02 0 04 0 06 0 08 Tq rot Nm 10 00 10 4 8 00 10 4 6 00 10 4 4 00 10 4 2 00 10 4 theta 0 00 100 0 00 0 02 0 04 0 06 0 08 som m VAWT Simulation Parameters Bx Simulation Parameters Loss Rho 1 2041 Viscosity 1 78000000e 05 Factors Elements 50 max Iterations 1000 Epsilon 0 0010 Analysis Settings Windspeed From Windspeed To Windspeed Delta Relax Factor 0 3 Windprofile pow Define Turbine Simulation 1 00 m s 15 00 m s 0 50 m s Start DMS Graph Curve Settings V Curve Points V Selected Op Point Figure 7 8 The turbine definition and simulation submodul
29. by specifying an annual windspeed distribution via the two parameters k and A of the WEIBULL distribution Thus the annual energy production can be calcu lated For further information about the turbine definition see section 6 5 7 5 Simulation settings 7 5 1 Simulation Parameters For a simulation the following user specific simulation parameters can be ad justed e fluid density p e fluid viscosity v e number of blade elements N e maximum number of iterations e maximum e for convergence e relaxation factor Wrelax 66 N The OBlade VAWT Module Define DMS Parameters Simulation Name Darrieus Turbine Simulation Corrections Variables Rho 1 20 kg m 3 Wiscosi 1 78e 05 ko ms Tip Loss t midi ol Discretize Blade into M Elements 50 00 Max Number of Iterations 1000 00 Variable Induction Factors Max Epsilon for Convergence 0 001 Relax Factor 0 35 Wind Profile Constant Power Law exponent Logarithmic surface roughness Figure 7 9 Simulation definition dialog The relaxation factor is implemented as Uk 1 Wrelax Uk 1 T 1 m relax Up O lt Wrelax lt 1 7 5 and the convergence criterion e is applied to the alteration rate of the interference factor Au The iterative process stops when either convergence or the maximum number of iterations is reached For further information see section 6 6 1 7 5 2 Wind profile Besides the above simulation parameters the turbine simulation add
30. ctors u varies over the azimuthal angle Consequently all upwind or downwind height dependent variables are averaged values for the respective zone at the chosen height position The azimuthal data is stored for every simulated height posi tion and therefore always height dependent too The blade forces and force coefficients for a single blade result from an integra tion over the whole blade length The rotor forces and force coefficients for all rotor blades depend on the number of blades and their resulting azimuthal po sition The tangential force has always the same direction as the blade flight path The direction of the lengthwise force is the inflow direction whereas the crosswise force is always perpendicular to the lengthwise force 74 Bibliography 1 BMU Kurzinfo Windenergie 2010 online Available from http www erneuerbare energien de inhalt 4642 Accessed 26 May 2010 2 DEPERROIS A XFLR5 Analysis of foils and wings operating at low reynolds numbers 2009 online Availiable from http xflr5 sourceforge net xflr5 htm Accessed 19 February 2010 3 DRELA M YOUNGREN H XFOIL 6 94 User Guide MIT Aero amp Astro 2001 4 GASCH R TWELE J Windkraftanlagen Grundlagen Entwurf Planung und Betrieb Teubner Wiesbaden 2007 5 HANSEN Martin O L Aerodynamics of Wind Turbines Earthscan London 2nd Edition 2008 6 VAN LANGEN P J Blade Optimization Tool User Manual ECN C 06
31. dules e blade design and optimization e rotor simulation e turbine definition and simulation The HAWT module additionally provides a characteristic graph submodule All modules will be discussed in greater detail on the following pages 2 2 Code structure An overview of the data objects storing the blades turbines polars and simula tion data as well as their relation to XFOIL can be found in Fig 2 1 360 Polar Object lift drag coeff Foil Object Polar Object Blade Object Turbine Object Geom Params Coordinates lift drag coeff Turbine Params camber Reynoldsnumber thickness alpha range Reynoldnumber full 360 alpha range rpm type losses cut in cut out twist chord length Stations Number of Blades p exrapolated Data OO Blade Object LL 360 Polar Objects Polar Extrapolation to 360 Foil Object Simulation Results Panel Sim alpha range Rotor Sim Object Turbine Sim Object Simulation Params Simulation Params elems epsilon elems epsilon corrections iter corrections iter Blade Data Objects Blade Data Objects Simulation lambdarange windrange Blade Data Object Sim Result data along the blades induction factors lift drag per length inflow angles circulation crit roughness lambda windspeed Figure 2 1 Data objects and data flow in QBlade 360 polar Object A 36
32. e In the turbine definition and simulation submodule the user can define and simulate a wind turbine To define a wind turbine a rotor blade must be present in the runtime database and the turbine parameters have to be specified The parameters that define a turbine are e rotor blade e cut in windspeed e cut out windspeed e turbine offset e fixed and variable losses 65 7 5 Simulation settings The cut in and out windspeed define the operational windspeed range of the turbine The turbine offset allows the positioning of a rotor on buildings with different heights where it experiences varying inflow velocities due to the nat ural wind profile caused by friction The fixed and variable losses account for gear and generator losses Furthermore the transmission can be selected The turbine angular speed can be a constant value variable or prescribed Either the constant angular speed for single speed turbines or the minimum and maximum angular speed for variable speed need to be defined For the latter a design opoint and corresponding TSR has to be selected For prescribed c the values can be set in a tabular The turbine simulation has to be defined by the selection of simulation parame ters a wind profile and corrections A turbine simulation is carried out over a range of windspeeds with the chosen incremental step size If a turbine simula tion has been conducted the user may calculate the annual yield of the turbine
33. e 6 17 Foil distribution along the blade without interpolation All elements whose centers lie between section 1 and section 2 are linked to the polar data from foil 1 The last airfoil at position Z is not included at all in the simulation From the element that lies just before section 2 to the first element that lies after section 2 there is a discontinuity as the foils rapidly change from foil 1 to foil 2 This is expressed in the simulation results if interpolation is not included When the foil interpolation is switched on the polar data that is used for the BEM computation of an element is a linear interpolation between the polar data of the bounding airfoils This interpolation more accurately represents a true blade geometry Strictly speaking the linear interpolation between two polars never represents the true polar of the intermediate airfoil This interpolation is just the most simple approximation to the real polar that is not present in the database However the accuracy can be arbitrarily improved by importing the geometric data for these intermediate airfoils and create new sections where the intermediate airfoils are placed Another possibility is to use XFOIL s dynamic 51 6 7 Simulation results coordinate mixing function where intermediate airfoil geometries can be created and simulated in XFOIL 6 7 Simulation results 6 7 1 Data storage and visualization There are two different types of simulation r
34. e spanwise velocity component that has not yet been taken into consideration is the vertical streamtube expansion that increases the stream tube crosssection The primary DMS model proposed constant interference factors for a whole ro tor half The differing azimuthal blade position and hence altering energy ex traction are unaccounted for To correct this simplification variable interfer ence factors can be selected Thus the iteration is executed for each azimuthal position in particular Other secondary effects like the influence of the tower wake struts guy ropes and dynamic stall are neclegted to date 68 7 The OBlade VAWT Module 7 6 Simulation results 7 6 1 Data storage and visualization Local and global variables In general there are local and global variables Local variables depend either on the local position such as height radius or azimuthal angle whereas global vari ables only depend on the simulated tipspeed ratio or windspeed and describe the whole rotor Rotor and turbine variables Rotor variables describe the rotor in a dimensionless manner Turbine variables whatsoever include turbine specific information from the turbine data in a tur bine simulation Plots Cp TSR 0 0 1 0 2 0 3 0 4 0 Figure 7 10 Rotor Graph Cp A and Blade Graph uup I Three different graph types are available in the OBlade VAWT module rotor graph blade graph and azimuthal graph The first one is destined for
35. ective Projection Axes W Positions Foil Names MEME suachtRotor mi Number of Blades 3 Radial Offset 0 02 m 0 562 m 0 531 m Insert before section 1 Insert after section 1 Delete section 1 0 500 m Height m Chord m Radius m Twistindeg irc Angle in de Foil TU 0 00 0 01 0 22 0 00 0 00 NACA 441i rado x 2 0 03 0 01 0 22 0 00 0 00 NACA 441i 0 406 m 3 0 06 0 01 0 22 0 00 0 00 NACA 441i 0 375 m 4 0 09 0 01 0 22 0 00 0 00 NACA 441i is m 0 312 m 5 012 0 01 0 22 0 00 0 00 NACA 4414 0 281 m 6 0 16 0 01 0 22 0 00 0 00 NACA 441i a 0 250 m 7 0 19 0 01 0 22 0 00 0 00 NACA 4414 ee 8 0 22 0 01 0 22 0 00 0 00 NACA 441i j ias m 9 0 25 0 01 0 22 0 00 0 00 NACA 441i 0 156 m 10 0 28 0 01 0 22 0 00 0 00 NACA 441i 0 125 m 1 0 31 0 01 0 22 0 00 0 00 NACA 441i orn 0 062 m 12 0 34 0 01 0 22 0 00 0 00 NACA 441 0 031 m 13 0 38 0 01 0 22 0 00 0 00 NACA 441i 0 000 m 14 0 41 0 01 0 22 0 00 0 00 NACA 441i 15 0 44 0 01 0 22 0 00 0 00 NACA 441i uv Modify Shape Scale J Optimize Back Save Figure 7 3 Blade design submodule The blade design and optimization submodule allows the rotor design for different VAWT types A blade consists of a finite number of blade sections In a tabu lar vertical radial and circumferential position chord length airfoil 360 polar and other parameters of each blade section can be defined Additionally scaling and optimization functionalities can be used to improve and
36. eed of the blade and Vo is the freestream inflow velocity A turbine simulation is generally executed for a range of windspeeds although in fact the windspeed is translated into a tipspeed ratio on the basis of the turbine data as well For each tipspeed ratio the iteration is executed at every height position for all upwind azimuthal angles streamtubes until the user defined convergence condition is met for either the whole rotor half constant u or the particular azimuthal position variable u In the process local and global charcteristic simulation data is stored and can be visualized after the calculation 7 1 5 Limitations Please note that there have been observed some convergence and plausibility problems for unrealistic geometries very high solidities as well as for low wind speeds high tipspeed ratios as the model does not consider backflow effects Consequently the results at high tipspeed ratios should not be trusted after the kinks of the power curve occur As most of the reference data does not show this area either it might be a general problem of the DMS algorithm that has to be reconsidered in the future 60 7 The OBlade VAWT Module 7 2 The blade design and optimization submodule QBlade v0 6 on XFLR5 v6 06 Co JCE eE File View Blade 360 Polar Turbine Options x ANN Rose 77 Rotor Blade VAWT ax 3D View Control Show v Turbine Surfaces V Outlines Airfoils Persp
37. eee E TE T BES PS ES 52 6 71 Data storage and visualization 92 0 2 Variable HSUfips s hu d oos br ede e 93 Contents 7 The QBlade VAWT Module 56 Ele DASS EAN AA ARA 56 7 1 1 Method of operation ss es sesana aa a eaa 56 7 1 2 The Double Multiple Streamtube Model 07 Z5 VELOCES ud dc a oe oe oo e e I Re od 59 74 Heraton DEOCOOUIB r gra ii eei ee o ea A oltre dos 59 noD Eia PTT T 60 7 2 The blade design and optimization submodule 61 lek Blade OPtUMIzZa O prm A e de dd 61 522 JDplade scalitig 2 239 ica o dad ER bo bt es 63 7 3 The rotor simulation submodule 64 7 4 The turbine definition and simulation submodule 65 220 Simulation Sette aoe Ga iva Reve ute SESS 66 7 5 1 Simulation Parameters 242 usce a a e e 66 Zo Wind POMC sudo a deu demi deos deese ded 67 7 0 0 COMECHONS yx kt 09 3 5E m AE m E Ee e age dod 68 726 Simulation resul ao o8 9 30 aa XC RACE C Re e ede Reg 69 7 6 1 Data storage and visualization 69 7 02 Natigble stes 6 EE Eo hae A ge s 70 Bibliography 74 1 Introduction Solving the worlds energy problems is one of the great topics of our time Re cently an increase in global awareness has led to a boom in the market for re newable energy technology To reduce the dependence on fossil fuels efficient power generation methods in the fields of solar wind wave biomass and ther mal energy are in dema
38. el by dividing the rotor into an upstream and downstream half Each one is repre sented by a separate rotor disk This double disk acts like two single actuator disks in tandem The subsequent iteration algorithm is hence executed twice for every streamtube Additionally the DMS algorithm is executed for each height position where the fluid flows through the respective blade section As already described a rotor blade is composed of several blade sections According to the selected number of elements the intermediate blade sections are interpolated from the given ge ometry All sections can be treated as independent 2D foils producing lift and 57 7 1 Basics Lateral view Upwind view Wind velocity profile F Streamtube 2 TW El s Downwind dea pal Upwind El E w E T p e BI E la ve T Rm f 2 El HE 2 5 Zo mmi lee V Sts j SJE A X Ie al um z izy 1 AD A gt a A ES ids j Blade element flight path ETE Rotor element ABCD replaced by two actuator disks in tandem Plan view m Figure 7 2 VAWT rotor geometry definition and two actuator disks in tan dem 16 drag as a function of their local angle of attack a The resultant total force on a blade can be found by integrating over the whole blade length Streamtube models combine the preceding approaches of the actuator disk the ory and the blade element method by iteratively balancing momentum cons
39. er vation and the forces on the rotor blades until system convergence is reached 58 7 The OBlade VAWT Module 7 1 3 Velocities There are five important velocities in a DMS calculation 1 inflow velocity Vio of the undisturbed freestream flow 2 upwind induced velocity V due to the energy extraction of the blade in the upstream rotor half 3 equilibrium velocity V in the plane between up and downstream rotor half represents wake ve locity of upstream rotor disk and inflow velocity of downstream rotor disk 4 downwind induced velocity V due to the energy extraction of the blade in the downstream rotor half 5 wake velocity V of the whole double disk According to these velocity determinations one can define the interference fac tors for the energy extraction in the up and downstream rotor half u E 7 2 V u V 7 3 e An interference factor of u 1 stands for zero energy extraction If u 0 the fluid velocity is slowed down to zero 7 1 4 Iteration procedure The iteration variable of the DMS algorithm is the interference factor u It can be variable or constant for all azimuthal positions streamtubes depending on user selection A rotor simulation is executed for a range of tipspeed ratios The global tipspeed ratio is the relative rotational speed of a VAWT rotor and is defined as Rw TSR 7 4 2 Ves Ae 59 7 1 Basics where R is the radius of the equator w is the angular sp
40. eristic Simulation ik Graph Curve Settings a 4 Curve Points Y Selected Op Point 0 Style Width Color mexicoBIGGERv222222 Figure 6 9 The multi parameter simulation submodule 40 6 The OBlade HAWT module mm QBlade v0 6 on XFLR5 v6 06 Lo LO mE File View Blade 360Polar Turbine Options 2 INVERSE J y 360 A N 4 Le AAN ALAN SN 3 Turbine Turbine Simulation Windspeed m s Baap t 9 MD New Turbine d New Turbine Simulation x 17 60 x HAWT mx HAWT Simulation Parameters mx me PIMI s INI Simulation Parameters pup 3 50 106 3 50 105 Tip Loss Rho Power Regulation Stall EUR Muze Transmission Single New Tip Loss Viscosity 1 77999991e 05 V Cut In 4 00 m s l 3 00 105 Root Loss Elements 100 V Cut Out 25 00 m s max Iterations 1000 j 2 50 10 Epsilon 0 0001 Rotational Speed 15 00 rpm Reynolds Drag Correction Relax Factor 0 2 2 00 106 2 00 105 Turbine Blade S88V3 6 1 50 10 1 50 105 Analysis Settings Outer Radius 44 45 m Fixed Pitch 0 00 m ven Define Turbine Simulation VariableLosses 0 000 Start 1 00 m s Fixed Losses 0 05 W 5 00 105 5 00 104 End 20 00 m s Create Edit Delete Turbine V m s V m s Delta 0 50 m s Create Edit 0 00 100 0 00 100 0 0 5 0 10 0 15 0 20 0 25 0 0 0 5 0 10 0 15 0 20 0 25 0 Start BEM Weibull Settings Graph Curve Settings k 0 01 4 Curve Points V Selected Op Point A 0 01 Style aa Annual Yield 100966083 Wh Hew
41. es its own wake during a revolution poses some new problems for the simulation and power analysis of such wind turbines Exten sive research including field tests and software development lead to a model introduced by Ion Paraschivoiu the Double Multiple Streamtube DMS model It considers the circular path of the blade and the energy extraction in 2 steps up and downstream of the rotational axis and will be the subject of a subsequent chapter 1 Introduction 1 2 The software project This software project is realized being a part of the wind energy group at the Berlin Technical University Department of Experimental Fluid Mechanics led by Prof Dr Christian Oliver Paschereit The aim of this project is to provide an open source turbine calculation software that is seamlessly integrated into XFOIL an airfoil design and analysis tool The motivation for this is to create a one solution software for the design and aerodynamical computation of wind turbine blades The integration in XFOIL enables the user to rapidly design cus tom airfoils and compute their polars extrapolate the polar data to a range of 360 and directly integrate them into a wind turbine simulation This step of exporting and importing foil and geometry data between different programs is skipped as well as the associated trouble At the same time the integration of the BEM and DMS code into XFOIL s sophisticated GUI will make this software accessible to a huge number of in
42. esign submodule defined for every rotor blade The hub radius must be specified which is the position where the blade root is connected to the hub of the turbine The radial positions of a blade can either be defined in blade coordinates where the positions are the distance from the blade root or in absolute coordinates where the positions are the total distance from the turbine s hub center The option pitch blade adds an offset to the rotorblades twist at every section of the blade When a blade design is finished the user can export the blade geometry either as a cloud of points or in the stl file format To export a blade geometry select in the top toolbar Blade gt Export Rotorblade Geometry 35 6 2 The blade design and optimization submodule Figure 6 3 Sections along a blade 6 2 1 Blade optimization While a blade is edited or created and every section is fully defined the user can optimize the blade geometry in the blade optimization dialog see Fig 6 4 Optimize HAWT Blade Geometry ax Optimize for Tip Speed Ratio MEET From Position 1 v to Position 17 Y Opt Twist Opt Chord None O None Opt Lift Drag deg Schmitz Stall at Tip Speed Ratio deg Betz Linear TatPos 1 deg Linear CatPos 1 m T at Pos 2 deg C at Pos 2 m Figure 6 4 Blade optimization dialog The user has to choose a tipspeed ratio Ag to optimize for and the sections po sitions that are to be optimized F
43. estigate the annual yield create another turbine simulation for the same turbine but with different simulation parameters and compare the results for example by isolating and comparing local curves create another turbine simulate it and compare the results 3 TUTORIAL How to create simulations in OBlade With the created foils and 360 polars VAWT s can be created and simulated us ing the same procedural method as for HAWT s VAWT p QBlade v0 6 on XFLRS v6 06 File View Blade 360Polar Turbine Options 2 R e ANN o 24 Rotor Blade 3D View Control Show V Turbine V Surfaces V Outlines F Airfoils Perspective Projection Axes T Positions 7 Foil Names MBE new vawr Blade EN Number of Blades 3 gt Radial Offset 0 10 m Isertbeforesecton i Insertaftersectioni Delete section 1 Chord m Radius m Twistindeg irc Angle in de Foil Polar I 0 05 010 0 00 0 00 NACA 0012 NACA 0012 2 0 05 0 39 0 00 0 00 NACA 0012 NACA 0012 3 0 05 0 48 0 00 0 00 NACA 0012 NACA 0012 4 0 05 0 49 0 00 0 00 NACA 0012 NACA 0012 5 0 05 0 50 0 00 0 00 NACA 0012 NACA 0012 6 0 05 0 50 0 00 0 00 NACA 0012 NACA 0012 7 0 05 0 50 0 00 0 00 NACA 0012 NACA 0012 8 0 05 0 49 0 00 0 00 NACA 0012 NACA 0012 9 0 05 0 48 0 00 0 00 NACA 0012 NACA 0012 10 0 05 0 39 0 00 0 00 NACA 0012 NACA 0012 1 0 05 0 10 0 00 0 00 NACA 0012 NACA 0012 4 n p Modify Shape Scale Optimize l Save N
44. esults for a BEM computation Global variables or rotor variables are values that characterize the rotor or turbine as a whole The Cp value is such a global variable Every increment of tip speed ra tio or wind speed that was simulated yields one Cp value The Cp over A curve gives only information about the overall rotor performance but not about the local events taking place at the blades These global variables are computed out of the local variables Every point in the Cp curve represents a BEM computation for one tipspeed ratio or windspeed The thrust T is calculated by adding up the normal forces acting on the elements The local variables or blade variables like the AoA a give insight in the local conditions at the blade Every curve of a local variable represents a BEM com putation for one tipspeed ratio or windspeed P IW 2 00 106 1 80 108 1 60 108 LP Ee ns z 1 20 108 Show all Rotor Curves 1 00 106 Hide all Rotor Curves Isolate Blade Curve 5 SORS Compare isolated Blade Curve Y Set as Rotor Graph Set as Blade Graph 6 00 109 5 ped Save View to Image File Ctrl I 2 00 107 V m s 0 00 100 0 Figure 6 18 Rotor graph to the left and blade graph to the right context menu In the context menu of a graph the user can set the graph as rotor graph to display global variables or as blade graph to display local variables 52 6 The OBlade HAWT module 6 7 2
45. flow conditions around the blades This implies the need for a large simulated domain as well as a fine spatial resolution A full CFD analysis that fulfills these requirements and accounts for all the named effects is very time 1 1 Blade design and simulation in the wind turbine industry consuming and expensive An alternative to CFD simulations are vortex meth ods with the limitation that they cannot model viscous behavior since they are based on potential flow theory That is why only 9 design and evaluation tools that are based on the Blade Ele ment Momentum BEM method are used to predict the efficiency of Horizontal Axis Wind Turbines HAWT in the industry business The use of other methods such as CFD RANS and vortex models is therefore narrowed to research environ ments The main advantage of the BEM model compared to CFD is that it is very cost efficient and the computational time is significantly less The prediction of a wind turbines performance operating in a fluctuating wind field complicates the application of the BEM method that assumes a steady state wind field The BEM model which is in fact a two dimensional method extrapolated into the third dimension applies semi empirical corrections derived from correlations with measurements or full CFD computations to account for three dimensional effects TANGLER states that in general the BEM underestimates the overall per formance of a Turbine and overestimates the peak powe
46. fore section 2 Insert after section 2 Delete section 2 Pos m Chord m Twist in deg Foil Polar 1 0 00 0 40 24 74 Circular Foil Circular Foil 360 Polar 2 0 62 0 40 24 74 Circular Foil Circular Foil 360 Polar 3 125 140 24 74 NACA 5518 NACA 5518 360 Polar 4 2 50 1 00 9 00 NACA 5518 NACA 5518 360 Polar 5 5 00 0 70 5 00 NACA 5518 NACA 5518 360 Polar 6 7 50 0 53 2 00 NACA 5518 NACA 5518 360 Polar 7 10 00 0 42 0 50 NACA 5518 NACA 5518 360 Polar Modify Shape Scale Pitch Blade 0 00 Optimize Back Advanced Design Save Figure 3 5 HAWT blade design and optimization submodule 1 press the HAWT Rotorblade Design button Pdl first blue button press New Blade 3 enter the blade data via the tabular see Fig 3 5 or configure your own blade using the Scale Optimize and Advanced Design options N 4 press Save 3 TUTORIAL How to create simulations in OBlade All rotors in the database can be simulated in the HAWT rotor simulation sub module Whenever a rotor simulation is defined all simulation parameters need to be specified Then the dimensionless simulation is conducted over the de sired range of tipspeed ratios The three graphs show the simulation results By double clicking on a graph the user may change the plotted variables By right clicking on a graph the graph type to display local or global variables can be set local variables are displayed in the same blade graph for all computed lambd
47. global and the other ones for local simulation data They can be switched by the appropriate selection in the context menu that appears after a right click on the plot 69 7 6 Simulation results 0 45 90 135 180 225 270 315 360 Figure 7 11 Azimuthal Graph blade tangential force coefficient single blade and rotor tangential force coefficient all blades here 3 7 6 2 Variable listings The plotted variables are selected by double clicking on the graph After a rotor simulation the following variables are available 1 global e power coefficient Cp e upwind power coefficient Cp downwind power coefficient Cp torque coefficient Cy upwind torque coefficient Cm1 e downwind torque coefficient Cm2 e power coefficient based on tipspeed Kp tipspeed ratio TSR inverse tipspeed ratio 1 TSR 70 2 local 7 The OBlade VAWT Module e height dependent relative height h relative radius chord c inclination angle upwind interference factor tup downwind interference factor Ugw upwind induction factor dup downwind induction factor Agw inflow velocity Vos upwind induced velocity Vup equilibrium induced velocity Veg downwind induced velocity Vaw wake velocity Vwake local upwind tipspeed ratio TS Rup local downwind tipspeed ratio TS Raw swept area S upwind tiploss factor Fup downwind tiploss factor Fa upwind iterations downwind iterations 71 7 6 Simulation results 72 e azimut
48. graph context menu Fig 2 3 in stead of displaying the whole set of blade variable curves the currently selected blade curve can be isolated and copared to the curve of other simulations if simulations with the same tip speed ratio or windspeed exist Each conducted Cp 0 6 0 5 Current Rotor gt 0 4 Current Graph 0 3 Show all Rotor Curves Hide all Rotor Curves 0 2 Isolate Blade Curve 0 1 Compare isolated Blade Curve v Setas Rotor Graph 0 0 2 0 4 0 6 0 8 0 Set as Blade Graph 0 1 Save View to Image File Ctrl I Figure 2 3 Graph and Graph Context Menu simulation is displayed as a single curve in the rotor graph the blade graphs show always a set of curves Each curve can be manipulated individually Fig 2 4 The color thickness and line style of a curve can be changed computed points can be displayed and a curve can also be hidden from view Graph Curve Settings 54 Curve Points V Selected Op Point Style Width Color Figure 2 4 Curve Settings 12 3 UTORIAL How to create simulations in QBlade This section will give a short introduction on how to design and simulate a rotor or turbine with QBlade Only the very basic functionalities are mentioned here and this is merely an overview in which succession the modules and submod ules are to be run through to create a blade and simulate it All the functions not mentioned in this part are more or less self explanatory and the user may e
49. gt Save Project As or press the Save button ii third black button 2 select a fitting project name and file location 3 press Save Later on this project file can be reloaded via the File menu as well 1 recently saved or opened project files are stored directly in the File menu and can be loaded by clicking on the desired file path 2 otherwise click File gt Insert Project or File gt Open or press the Open button pa second black button 3 select the desired project file 4 press Open A project can be closed via the File menu by clicking File gt Close the Project To create a new project the user can either click File gt New Project or press the New Project button Y first black button 28 4 XFOIL and XFLR QFLR The software XFOIL is a program to analyze and compute the flow around sub sonic isolated airfoils It is a standard software for the calculation of profile po lars XFOIL has been validated against other numerical methods and against experimental data for low angles of attack 20 for high angles of attack 19 The source code is released under the GNU General Public License The first ver sion was written in 1986 by MARK DRELA The goal was to combine a high order panel method with the new fully coupled viscous inviscid interaction method developed by DRELA and GILES at the MIT 3 Since then the software has undergone numerous revisions and has developed from a simple command line tool to a c
50. hal azimuthal angle 0 iterations interference factor u induced velocity V relative velocity W Reynolds number Re tiploss factor F angle of attack lift coefficient Cr drag coefficient Cp lift to drag ratio 5 normal force coefficient C tangential force coefficient C blade tangential force coefficient CF blade lengthwise force coefficient CF blade crosswise force coefficient CF rotor tangential force coefficient CF tot rotor lengthwise force coefficient CF tot rotor crosswise force coefficient CF tot 7 The OBlade VAWT Module In a turbine simulation the dimensionsless height and radius are replaced In addition to the other above mentioned variables a turbine simulation provides 1 global e power P W e torque T Nm e windspeed V m s e angular speed w rpm e power including losses Pjoss W e power coefficient including losses Cp Joss e WEIBULL probability hy e WEIBULL probability windspeed hy V m s 2 local e height dependent height m radius r m e azimuthal blade torque T blade lengthwise force Ex tot blade crosswise force Fy tot rotor torque Ttot rotor lengthwise force Fy tot rotor crosswise force Fy tot 73 7 6 Simulation results For constant interference factors the iteration gives one value each for the up wind and downwind zone for all height dependent upwind and downwind data u a TSR F iterations etc For variable interference fa
51. he rotational speed Additionally the user selects a desired tipspeed ratio Ay From this ratio a rotational speed is computed for every given wind speed during the simulation If the computed rotational speeds are lower or larger than the bounding minimum or maximum values these values give the rotational speed The turbine parameters that define a turbine are e rotor blade e cut in windspeed e cut out windspeed e fixed losses e variable losses For every turbine the rotor blade needs to be defined This can be any blade that is stored in the runtime database At the cut in windspeed the turbine starts and at the cut out windspeed the turbine stops operation To account for power losses that are not of aerodynamical nature but are caused by the efficiency of the generator and the gearbox a value for fixed losses and a value for variable losses can be selected The equation in which these losses are implemented is Pout 1 Ko Po v P fixed 6 8 in which ky is the variable loss factor and Prjxeq the fixed loss factor If a turbine simulation has been conducted the user may calculate the annual yield of the turbine by specifying an annual windspeed distribution via the two parameters k and A of the WEIBULL distribution The probability for a wind 42 6 The OBlade HAWT module P W 2 20 106 0 Variable Loss r 0 Variable Loss 2 00 10 0 1 Variable Loss 1 80 106 0 1 Variable Loss 1 60 106 0 05 bg Loss 0
52. he undisturbed air velocity Vo and the rotational speed w of the moving blade The relative velocity at the blade is W Vo Rw 7 1 and the angle of attack of the airfoil section is the angle between the relative velocity W and the chord line c The resultant force on each airfoil section can either be decomposed in lift and drag or in tangential and normal components The lift and drag coefficients for all angles of attack are already known in terms 56 7 The OBlade VAWT Module Figure 7 1 Relative velocity 15 and forces on a VAWT blade cross section 16 of the extrapolated 360 polars The tangential force drives the turbine and is hence vitally important for the calculation of the power coefficient 7 1 2 The Double Multiple Streamtube Model Concept This model has been developed by Ion Paraschivoiu for the performance analy sis of Darrieus type rotors It is basically a derivation of the actuator disk theory and the blade element theory The streamtube flowing through the VAWT rotor is splitted up into a set of smaller streamtubes The blades of the rotor pass through each of these stream tubes on their 360 degree path and extract energy from the fluid by reducing its velocity Thus the standard actuator disk theory can be applied for every streamtube in particular Due to the circular path of a VAWT blade it passes each streamtube twice These two steps of energy extraction are taken into consideration in the DMS mod
53. is implemented in combination with the Prandtl tiploss correction 49 6 6 Simulation settings 3D correction after Snel Himmelskamp discovered in 1945 that the maximum lift coefficient of profiles on a rotating rotor blade is significantly higher than the maximum lift coefficient of the same profile measured on a stationary rotor The centrifugal force accelerates the boundary layer radially this results in a thinner boundary layer where the stall is delayed At the same time air flowing radially in a rotating reference system generates a Coriolis force opposite to the rotational direction of the rotor This force is opposing the rise in pressure of the profiles suction side and delays the stall even more This effect is called stall delay or Himmelskamp effect and can be taken into account by modifying the two dimensional profile data For the affected profiles the stalled region will shift to higher angles of attack With a Viscous Inviscid Interaction Method Snel et al investigated the flow around a rotating rotor blade and developed a semi empirical formula to correct 2D profile data 17 based on these investigations According to Snel only the lift but not the drag coefficient needs to be modified Reynolds number drag correction The changes in lift and drag polars due to Reynolds number effects are not in cluded in OBlade The polars are always computed for a fixed Reynolds number During the simulation of a turbine the Reyn
54. itionally al lows the specification of an inflow wind profile There are three possible choices 1 constant uniform velocity profile like in a rotor simulation 2 power law Voo Z Vref 2 7 6 67 7 5 Simulation settings where ref is the simulated windspeed Zref is the equator or half hight position of the turbine and a is the roughness exponent e g 1 7 0 143 for open land and 0 11 for open water 3 logarithmic i log 2 z V Voo Z Uref x 7 7 with the already stated settings for vref and Zref and the surface roughness zo depending on the surroundings of the wind turbine e g zy 0 2mm for open water and zy 2 m for highly built up areas 7 5 3 Corrections To take account for the finite length of the blade a tiploss factor can be included in the DMS algorithm Due to the pressure difference between the upper and lower surface of the airfoils downwash and a spanwise velocity component can be observed regarding a real blade These two effects result in a decreased energy extraction at the blade tips Therefore the tiploss factor assumes values from 0 to 1 and is F 1 in the middle of the blade and F 0 at the end section It is introduced into both actuator disk theory and blade element method by altering the angle of attack the relative velocity W the lift and drag coefficients cr and cp and by considering the downwind induced angle of attack o Another effect of th
55. le chord twist and length With the momentum theory the relative windspeed for every sec tion can be computed This allows the calculation of the angle of attack and the derivation of the lift and drag coefficients of the respective profile out of a table With these coefficients and the area of an element the normal and tangen tial force components thus the thrust and torque of an element are computed The elements contributions can then be added up to yield the final thrust and torque of the whole rotor For different ratios of windspeed and angular speed characteristic curves and quantities of the rotor can be computed 6 1 2 Iteration procedure The iteration variables of the BEM method are the axial and radial induction factors which are defined as Asin p B c aC 6 1 y sin cos s nm aC 1 m 33 6 2 The blade design and optimization submodule with the inflow angle q the tangential and normal force coefficients C and Cy and the rotor solidity c which is the part of an annular element that is covered by blades cb In this equation c is the chordline and B the number of blades Rotor plane Figure 6 1 Velocities at the rotor plane 5 Figure 6 1 shows the velocities at the rotor plane If the induction factors are known it it possible to compute the inflow angle p gives the angle of attack the angle between the airfoil s chordline and the relative windspeed experienced by the rotating
56. lem during the iteration loop of a BEM computation is the fluc tuating behavior of the axial induction factor The reason for this fluctuation is the periodical switching of the turbines loading state between light and heavy loading 8 see section The turbulent wake state This may lead to a stop of the iteration after the maximum number of iterations is reached and impacts both the code s performance and its accuracy In 8 MAHERI proposes to introduce a relaxation factor Wrejax to overcome these fluctuations The relaxation factor is introduced in the iteration after a new value 2 4 for the axial induction factor has been calculated Ak 1 Wrelax4k41 F 1 m Wrelax 4k r Oe Wrelax lt L 6 15 The convergence rate of the BEM code strongly depends on the initial guess value for the axial induction factor If the initial guess a 0 in this implemen tation is in the neighborhood of the final result convergence is achieved signifi cantly faster To further accelerate the convergence rate of the BEM code MAHERI proposes that for the first few iterations a relaxation factor Wrelax 1 should be 46 6 The OBlade HAWT module Axial induction factor 20 Iteration Figure 6 14 Fluctuation of the axial induction factor around the light and heavy loading state 8 0 583 0 533 0 483 Hooo ple HA ft EL fae 0 433 Axial induction factor 0 383 0 333 amp Iteration Figure
57. mputation with WEIBULL distribution 1 2 The software project e manual selection of BEM and DMS correction algorithms e manual selection of all relevant simulation parameters data browsing and visualization as post processing export functionality for all created simulation data blade geometry export in stl format storing of projects rotors turbines and simulations in a runtime database 2 Software implementation 2 1 Code limitations Like the original XFOIL written by MARK DRELA and XFLR written by ANDRE DEPERROIS OBlade has been developed and released according to the princi ples of the General Public License One important point about the GPL is that this program is distributed without any warranty neither the warranty of mer chantability nor the warranty of fitness for a particular purpose The resulting software is not intended as a professional product and does not offer any guar antee of robustness or accuracy It is distributed as a personal use application only This software may not be faultless and there will certainly be more bugs discovered after the distribution However a validation against other BEM soft ware permits some trust in the provided results 2 2 Code structure The OBlade 360 extrapolation module allows an extrapolation of the AoA to a range of 360 There are two different methods available the Montgomery and Viterna extrapolation The OBlade HAWT and VAWT modules both consist of three submo
58. mulation object is deleted all associated blade data objects are deleted tool Blade data object Blade data objects are created automatically during a simulation They store the data that is computed for the elements along the blade What s more one blade data object is created for every or windspeed increment of the simulation The blade data objects require the most memory space 2 3 Plotting results Graph controls OBlade inherits the Graph cpp and OGraph cpp classes from XFLR5 which are very convenient to display simulation results in various ways Each Graph can be manipulated with the mouse Using the mouse wheel zooms in and out of a graph Zooming in and out while pressing X or Y on the keyboard only zooms the corresponding axis By double clicking on a graph Fig 2 2 the user can specify variables for the X and Y Axis such as plotting the Cp value over the tip speed ratio By right clicking on a graph the type of graph can be specified 11 2 3 Plotting results Graph controls gt Graph Settings LN xS Variables Scales AxisandGrids Fonts and BackGround YAxis vs XAxis Power Coefficient Cp Power Coefficient Cp Thrust Coefficient Ct Thrust Coefficient Ct Moment Coefficient Cm Moment Coefficient Cm Kp Kp Tip Speed Ratio Tip Speed Ratio 1 Tip Speed Ratio 1 Tip Speed Ratio Restore Apply OK Cancel Figure 2 2 Defining Variables in Graph Settings see Data storage and visalization Also in the
59. n Relax Factor 0 2 Analysis Settings Tip Speed Ratio Start Tip Speed Ratio End Tip Speed Ratio Delta Graph Curve Settings 4 Curve V Selected Op Point S88V3 S88V3 Simulation S88V3 Simulation 2 screenshots Figure 6 8 The rotor simulation submodule In the rotor simulation submodule the user can commit rotor blade simulations over a range of tipspeed ratios A rotor simulation can only be defined when at least one rotor blade is present in the runtime database When defining a rotor simulation the user has to select the desired corrections to the BEM algorithm and the simulation parameters Once a simulation is defined the user can select a range of A values tipspeed ratios and the incremental step for the simulation A rotor simulation is always carried out dimensionless The freestream velocity is assumed to be unity and the rotor radius is normalized for the computation This implies that no power curve or load curves like the bending moment can be computed during a rotor simulation 39 6 4 The multi parameter simulation submodule 6 4 The multi parameter simulation submodule In the multi parameter simulation submodule simulations can be carried out over a specified range of windspeeds rotational speeds and pitch angles To limit excessive usage of memory only the rotor graph curves are stored as a simulation result By right clicking on a graph the user can specify the main v
60. nd In Germany wind energy plays a central role to reach the goal of an almost carbon dioxide free energy production till 2050 1 Because there is a limit to the number of adequate sites for turbines that do not interfere with natural protection laws or residents a part of the strategy to keep the de velopment of wind energy on a high level is to replace older turbines at good wind sites with newer more efficient ones A condition for an efficient conversion of the wind energy into mechanical en ergy with wind turbines is the optimal design of the rotor blades Methods for rapid development reliable and robust predictions of the aerodynamic charac teristics and simulation of the flow conditions around a rotor blade are essential for this design task 1 1 Blade design and simulation in the wind turbine industry The blade design methods for wind turbines originate from the aircraft design industry and apply the same techniques But the flow conditions that a turbine blade experiences are quite different from those affecting a plane Hence a lot of the assumptions made in flight aerodynamics cant t be applied to the complex flow field around a wind turbine The latter is unsteady three dimensional tur bulent roughly incompressible and often separated from the flow contour The aerodynamics of a wind turbine are influenced by far field conditions far up and downstream from the rotor At the same time they depend on small scale turbulent
61. nstant In reality there are large variations in the wind velocities e In the area of the blade root and close to the blade tip the finiteness of the blades leads to vortices being shed This results in a loss of energy extraction e The rotation of the rotor is only considered in the velocity distribution along the blade but leads to a dynamic pressure gradient that particularly affects detached flow e The blades boundary layer is subject to centrifugal forces e Centrifugal pumping a radial flow along the blades caused by Coriolis forces and the radial pressure gradient occurs e The momentum balance is only valid in the rotor plane Bending of the blades out of the rotor plane leads to errors Different often semi empirical correction algorithms to account for these effects exist The following ones can be selected to be included in the OBlade BEM simulation e Prandtl tiploss 7 e Prandtl rootloss 7 48 6 The OBlade HAWT module e New tiploss model after Shen et al 13 e New rootloss model after Shen et al 13 e 3D correction after SNEL 17 e Reynolds number drag correction from Hernandez and Crespo 18 e Airfoil interpolation Any combination of these corrections can be added to a simulation with one ex ception The tip or rootloss model after Shen can never be used in combination with the Prandtl root or tiploss model That is because the Prandtl tiploss factor F is included in the models by Shen a p
62. olds number is changing for every operational point The user should carefully check how large the deviation is for every individual case Hernandez and Crespo 18 suggested a correction in which the lift polar remains unchanged and the drag polar is corrected by scaling the drag coefficient inversely with the Reynolds number Rep 0 2 Cp Cp Ref a 6 17 In 6 17 Reres depicts the Reynolds number for which the polar data was com puted It is important to note that this correction represents a very simplistic approach to the estimation of the drag coefficient Especially for low Reynolds numbers the drag behavior can be very complex 50 6 The OBlade HAWT module Foil interpolation The foil interpolation in effect is not a correction to the BEM algorithm It merely is the most simple solution to a problem that arises during the discretiza tion of the blade As stated previously a blade is defined in sections Every section may have a different airfoil that defines the sections geometry The ge ometry in between two sections of a real blade is a liner interpolation between the two airfoils The problem now is that only polar data for the airfoils at ev ery section but no data for the interpolated airfoils in between are present in the database If the option Foil interpolation is not selected the BEM treats the blade as in Fig 6 17 Section 1 Section 2 Section I Section Z Foil 1 Foil 2 Foil i Foil Z Element Figur
63. ond blue button press Define Rotor Simulation enter the simulation parameters and select corrections see the groupbox in the top right corner of Fig 3 6 enter a tipspeed ratio range from 1 to 17 and an increment of 0 5 press Start BEM explore the created simulation data by changing plot variables and graph types create another rotor simulation for the same rotor but with different sim ulation parameters and compare the results for example by isolating and comparing local curves create another rotor simulate it and compare the results p en press the Multi Parameter BEM Simulation button EF nied bine but ton to explore the HAWT multi parameter simulation submodule for pa rameter studies 3 TUTORIAL How to create simulations in OBlade In the HAWT turbine definition and simulation submodule a turbine can only be defined if a blade is already stored in the database The user specifies all turbine parameters and saves the turbine Afterwards a turbine simulation over a range of windspeeds can be conducted When the user sets the k and A values for the WEIBULL distribution the annual yield is computed automatically bm QBlade v0 6 on XFLR5 v6 06 File View Blade 360Polar Turbine Options 2 Re AA as rr ALVA Y Turbine Turbine Simulation Windspeed m s 9 ti New Turbine y New Turbine Simulation HAWT mx P Ww HAWT Simulation Parameters Simulation Parameters Turbine Data pa
64. r 14 But nevertheless the blade element momentum method is widely applied in the wind turbine industry because the use of analysis techniques of such lower order accuracy greatly simplifies the turbine design Thanks to the BEM model it is possible to rapidly develop and test different rotor designs against one another commit small changes and test again and in this way evolve a preliminary design that can be studied in greater detail with other techniques like CFD later The power of this iterative approach and the verification of BEM simulations with wind tunnel and field measurements justify the use of BEM computational methods to analyze the blades from a two dimensional point of view The BEM method s ability for robust analysis and low computational costs make up for most short comings and inaccuracies Virtually all modern HAWT rotors were designed using this model Recently a new interest in Vertical Axis Wind Turbines VAWT has can be ob served One reason is their ability to capture wind from all directions which is utile in urban areas where no main wind direction can be found because of numerous barriers buildings trees etc and flow channelling effects However the installation of small scale VAWT s on the top of large building is a new idea to support the production of clean energy in urbanized areas Another approach is the development of huge vertical offshore applications Though the rotation of a VAWT blade that pass
65. reate 360 Polar Save 360 Polar Alpha deg v Compare 360 Polars Style Width Color Figure 3 4 360 polar extrapolation module press the Polar Extrpolation to 360 button 360 button select the Montgomery radio button and press Create New 360 Polar 3 configure the initial polar via the Cpoo value the A and B sliders and press Save 360 Polar 4 click 360 Polar gt Generate a Circular Foil N E 17 If one or more 360 polars have been created a blade can be designed in the HAWT and VAWT blade design and optimization submodules The Optimize and Scale buttons open the corresponding dialog windows Stations can be added or removed one airfoil and one 360 polar has to be specified at every section Ad ditionally every blade has a Number of Blades that predefines of how many blades the future rotor consists When a blade is fully defined it can be saved Instead of creating a new blade it is possible to edit stored blades Whenever this is done only a copy of the previous blade is edited 18 p QBlade v0 6 on XFLR5 v6 06 Le JLS mE File View Blade 360Polar Turbine Options x e ANNS m ZA UL Rotor Blade New HAWT Blade HAWT Bx 3D View Control Show W Turbine V Surfaces Y Outlines Airfoils Perspective Projection Axes Positions 7 Foil Names WE New HAWT Blade s Number of Blades 3 Hub Radius 0 20 m V Blade Coordinates Insert be
66. riori Prandtl tip and rootloss The Prandtl tiploss factor is an approved procedure for the correction of profile data to get a better agreement between measured and computed data Prandtl modeled the helicoidal vortex sheet wake behind the rotor as a succession of solid disks moving with the wake Prandtl s analysis can be found in detail in 7 In combination with the tiploss model a rootloss model is often used to account for the influence of the vortex shedding at every blade s root on the induction factors New tip and rootloss after Shen In 2005 Shen examined the various tiploss models by Prandtl Wilson amp Lis saman and Mikkelsen that are used in modern BEM computations He found that they all lack rigorous consistency when the tip of the blade is approached 13 At the tip the tiploss factor F always tends to zero thus the axial induction factor tends to unity This implies that the axial velocity and the angle always tend to zero at the tip no matter what shape pitch or other airfoil parameters On the other hand he found that the Prandtl correction overestimates the loads at the tip when compared to experimental data Based on data from the NREL experimental rotor he proposed a new tiploss model to overcome these incon sistencies Based on the assumption that the force should tend to zero at the tips because of pressure equalization he introduced a new correction term to cor rect the force coefficients C and Cz It
67. rom this tipspeed ratio an assumed inflow angle is computed for every section i 2 uu l E jg tan wem 5 6 5 Optimize for lift drag sets the twist at the specified Ag jo at which the blade section operates to an AoA that yields the highest glide ratio The option to de crease or increase this angle exists for the case that the AoA yielding the highest glide ratio is close to the stall point If the user optimizes for stall the twist is set in such a way that all the stations at the same time experience stall at the selected Ay value The third option allows to set a linear twist The chord distribution can be optimized according to BETZ 4 p 202 16 mR 1 c r 9 BCA f ed 6 6 36 6 The OBlade HAWT module or SCHMITZ 4 p 202 1 1 R c r pS sin tan 35 6 7 10 T A t m 1 min L a SN L Betz EA T EH TR R 0 1 1 Aa 10 Figure 6 5 Comparison of dimensionless chord distribution after BETZ and Schmitz 4 It is important to note that Cz is computed from the expected angle Ag and the twist angle for every station individually It may happen especially for stall blades that a low Cy value at Ag causes a very high value for the chord This is not a failure of the optimization equations One has to be careful with large chord values The value for solidity 7 lt the section of an annulus
68. ross platform compatible C Qt4 tool XFLR 2 OFLR with a so phisticated GUI While the software was ported and some additional modules like calculations with the vortex lattice method were added the algorithms for the foil analysis are exactly the same as those in the original XFOIL code There fore the XFOIL 6 94 User Guide 3 is still valid for all the different versions and can be consulted for further details XFOIL s features that are relevant for OBlade are e viscous or inviscid analysis of an airfoil considering forced or free transition transitional separation bubbles limited trailing edge separation lift and drag predictions just beyond stall e airfoil design and redesign by specification of a surface speed distribution e airfoil redesign by interactive specification of new geometric parameters e blending of Airfoils e import of airfoil geometry 29 5 The QBlade 360 extrapolation module 5 0 1 Basics During a revoultion a wind turbine blade experiences much higher angles of attack than the wing of an airplane For stall regulated wind turbines the flow phenomenon is even used as a means to limit the produced power As stall is generally avoided in aeronautical engineering the coefficients corresponding to high AoA are not of interest and therefore not available Additionally AoA in the post stall range may occur temporarily during the QBlade iteration proce dures Thus polar data for all possible 360 AoA h
69. speed up the blade design process 7 2 1 Blade optimization e Straight blades The Giromill and H Darrieus rotor are straight bladed VAWT rotor geome 61 7 2 The blade design and optimization submodule 62 aa gt Figure 7 4 Blade shapes straight helical Sandia and Troposkien tries Their airfoil sections all have the same radius and circumferential position that has to be set in the optimization dialog Helical blades The helical blade shape takes account of destructive torque pulsations re sulting from the finite number of blades By altering the cirmcumferential position of the sections the torque production is spread evenly over the blade revolution The circular angles of a helical blade can be defined for a start and end section in the optimize dialog the intermediate angles are derived from a linear interpolation Troposkien shaped blades The Troposkien shape is the shape of an idealized rope that is attached at its ends and rotated around a vertical axis As a rope transmits only drag forces and no bending moments this shape is used to reduce the stress experienced by VAWT blades In the optimization dialog the radial maxi mum deflection of the blade from the rotation axis needs to be defined Sandia shaped blades To simplify the blade manufacturing process of Darrieus wind turbines the Troposkien shape can be approximated by a circular arc segment and two straight line parts This approximation
70. terested people without the usual command line interface software tools The software is especially adequate for teaching as it provides a hands on feeling for HAWT and VAWT rotor design and shows all the fundamental relationships and concepts between twist chord foils turbine control and type and the power curve in an easy and intuitive way The GUI serves as a post processor to conducted rotor simulations as well and gives deep insight into all relevant blade and rotor variables for verification to compare different rotor configurations or even to study the numerical algorithm and the dependencies among the aerodynamic variables In addition to that the soft ware at hand is a very flexible and user friendly platform for wind turbine blade design Hence it can also act as a modular system for future implementations that can exploit the possibilities that a combination of manual and parametric airfoil design and analysis coupled with a blade design and simulation tool of fers The functionality of the BEM software includes the following features e extrapolation of XFOIL generated or imported polar data to 360 AoA e advanced blade design and optimization including 3D visualization us ing XFOIL generated or imported profiles e wind turbine definition rotor blade turbine control generator type losses e computation of rotor performance over range e computation of wind turbine performance over windspeed range e annual yield co
71. that is covered by blades must be between zero and unity For a section whose solidity is greater than unity the BEM algorithm does not converge Attention has to be paid especially in the root region because both the BETZ and the SCHMITZ equation lead to large chord values here 6 2 2 Blade scaling Scale HAWT Blade Dlg Reference Pos Scaling 44 450 44 450 m 1 000 7 Chord Scaling 0 700 0 700 m 1 000 Twist Scaling 0 00 0 000 1 000 ca Figure 6 6 Scale blade dialog 37 6 2 The blade design and optimization submodule The scale option allows to scale the blade s twist chord and or position This can be done by simply giving a new value for the variable that is scaled The scaling ratio is then computed automatically 6 2 3 Advanced design r p QBlade v0 6 on XFLR5 v6 06 floja File View Blade 360Polar Turbine Options NVERSE RER NNS o Lo d NS Rotor Blade Pu HAWT Bx 3D View Control Show E Turbine V Surfaces Y Outlines E Airfoils Y Perspective Projection Axes E Positions E Foil Names OqmetB oe insertAfter Delete Section Position m Offset m dihedral in deg ead Axis X 96 cha ead Axis Z a 0 00 0 00 0 00 0 25 2 1 50 0 00 0 00 0 25 3 3 50 0 00 0 00 0 25 4 6 50 0 00 0 00 0 25 5 8 00 0 00 0 00 0 25 6 11 00 0 00 0 00 0 25 7 14 00 0 00 0 00 0 25 8 17 00 0 00 0
72. xperiment freely with them 13 Figure 3 1 shows the start screen of QBlade From the main toolbar or the File menu the user can navigate through OBlade s functionalities The main toolbar contains the following buttons from left to right The black ones provide simple file loading and saving functions The red buttons belong to XFOIL and XFLR functionalities The 360 polar extrapolation module can be opened by clicking on the 360 button HAWT and VAWT related submenus are displayed by se lecting the blue and green buttons respectively The 360 polar extrapolation as well as the HAWT and VAWT menu points distinguish QBlade from XFLR More information about XFOIL and XFLR5 in general can be found in 3 and 2 bm QBlade v0 6 on XFLR5 v6 06 EN ex File Options Ge ANS NH sh 4 Figure 3 1 ObBlade startup screen 14 3 TUTORIAL How to create simulations in OBlade The tutorial starts in the Airfoil Design module In the run up to creating a rotor all its airfoils and the corresponding polar data need to be defined Airfoils can be created using splines a NACA airfoil generator or via an import function in XFLR5 In this case the NACA 5518 is loaded Je QBlade v0 6 on XFLR5 v6 06 t P F PR 26 1 4 E rens 1 Spline Foil NACA 5518 NACA Foils 4or 5 digits Number of Panels AFoil Bx Name hickness at 96 Camber at Points E Flap deg TEXHinge TE YHinge Show

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