Aeroelastic models for wind turbines

Transcription

1 Aeroelastic models for wind turbines how accurate does the flow model have to be? Helge Aagaard Madsen Georg Pirrung Torben J. Larsen Section Aeroelastic Design Department of Wind Energy

2 How accurate does the flow model have to be? EU project: Prediction of Dynamic Loads and Induced Vibrations in Stall STALLVIB, Helge Aagaard Madsen (Risø), Jørgen Thirstrup Petersen (Risø), Anders Björck (FFA), Hans Ganander (Teknikgruppen AB), Danny Winkelaar (ECN), Arno Brand (ECN), Albert Bruining (DUT), Mike Graham (IC), Peder Enevoldsen (Bonus), Stig Øye (DTU) 2

3 Aerodynamics of a blade section EU project: Prediction of Dynamic Loads and Induced Vibrations in Stall STALLVIB, Helge Aagaard Madsen (Risø), Jørgen Thirstrup Petersen (Risø), Anders Björck (FFA), Hans Ganander (Teknikgruppen AB), Danny Winkelaar (ECN), Arno Brand (ECN), Albert Bruining (DUT), Mike Graham (IC), Peder Enevoldsen (Bonus), Stig Øye (DTU) 3

4 Aerodynamic damping of a blade section EU project: Prediction of Dynamic Loads and Induced Vibrations in Stall STALLVIB, Helge Aagaard Madsen (Risø), Jørgen Thirstrup Petersen (Risø), Anders Björck (FFA), Hans Ganander (Teknikgruppen AB), Danny Winkelaar (ECN), Arno Brand (ECN), Albert Bruining (DUT), Mike Graham (IC), Peder Enevoldsen (Bonus), Stig Øye (DTU) 4

5 How accurate does the flow model have to be? Do we model the relevant flow phenomena? If we do: then the required model accuracy depends strongly on the aerodynamic damping of the mode shape in the operational point Model accuracy important for the quasy steady aerodynamic loads 5

6 Outline Introduction to aeroelastic modelling Flow phenomena we want to be simulated by the aeroelastic code Conclusions 6

7 Introduction to aeroelastic models 7

8 Aeroelastic models aeroelastic models used for time simulations on complete turbines including control, turbulence loading, hydrodynamic effects, wave loading and wake loading simulating on a PC from just below real time to several times real time used by industry for design, analysis and certification of turbines 8

9 Aeroelastic models with engineering aerodynamic sub models FLEX5 BHAWC BLADED PHATAS GAST FAST Cp-Lambda HAWC2 Stig Øye at DTU Siemens Originally developed by Garrad Hassen ECN NTUA NREL POLIMI DTU, AED Structural model parts differ as well as details of implementing sub models for aerodynamics, turbulent inflow, control etc. 9

10 The HAWC2 code Hydro-aero-servo-elasticity of floating turbines Aero-servo-elasticity of Onshore turbines Hydro-aero-servo-elasticity of offshore bottom fixed turbines Structural Dynamic Aerodynamic Controller & Actuators Hydrodynamic buoyancy Mooring system 10

11 Turbulent inflow modelling Turbulence model generated e.g. with the Mann model 11

12 Rotational sampling of the turbulent inflow has influence on aerodynamic modelling 12

13 Flow phenomena we want to simulate by an aeroelastic code 13

14 The flow characteristics of a rotating blade 14

15 The flow phenomena we want to simulate in a BEM type code steady induction tip flow effects tip correction dynamic induction yawed (skewed) inflow dynamic stall shed vorticity trailed vorticity influence of pressure field from wake rotation 15

16 Steady induction, tip correction -- uniform, inflow Good correlation between high fidelity models and the BEM engineering models -power and thrust within 1% H. Aa. Madsen et al. (2011) Blade element momentum modeling of inflow with shear in comparison with advanced model results, WIND ENERGY Wind Energ. Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: /we

17 Steady induction sheared inflow Deviations between high fidelity models and the BEM engineering models H. Aa. Madsen et al. (2011) Blade element momentum modeling of inflow with shear in comparison with advanced model results, WIND ENERGY Wind Energ. Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: /we

18 Steady induction rotor plane deviating from a plane disc are the associated flow characteristics modelled? Jeppe Johansen and Niels N. Sørensen Aerodynamic investigation of Winglets on Wind Turbine Blades using CFD, Risø-R-1543(EN), Risoe National Laboratory, February

19 Steady induction rotor plane deviating from a plane disc Simulations with an Actuator disc model with uniform loading BEM theory gives the same constant velocity for all rotor shapes Helge Aagaard Madsen and Flemming Rasmussen (1999) The Influence on Energy Conversion and Induction from Large Blade deflections. Proceedings of EWEC conference held in Nice, 1999, 19

20 Steady induction rotor plane deviating from a plane disc a method to model this in a BEM approach HAa Madsen et al. (2009) Validation and modification of the Blade Element Momentum theory based on comparisons with actuator disc simulations, Wind Energ. 2010; 13: Published online 25 August DOI: /we

21 Dynamic induction Model induction time lag from: collective pitch How well does it work for: individual pitch? blade motion? turbulent inflow? 21

22 Dynamic induction turbulent inflow Do we model the 1p, 2p etc. aerodynamics accurately? 1p, 2p variations in induction not modeled in most of the BEM type codes used by industry The BEM model is based on the Glauert propeller theory - probably not originally intended to be used on rotors of 100m D or more in atmospheric turbulent flow. 22

23 Dynamic induction BEM implementation aspects Standard approach induction constant in a ring element HAWC2 implementation - induction computed at each time step in all grid points 23

24 Dynamic induction turbulent inflow 24

25 Dynamic induction -- introduction of a near wake model Model for computation of induction Near wake model Far wake model Model for trailed vorticity Model for shed vorticity HÁa Madsen and F Rasmussen (2004) A Near Wake Model for Trailing Vorticity Compared with the Blade Element Momentum Theory, Wind Energ. 2004; 7: (DOI: 25

26 Dynamic induction -- introduction of a near wake model The near wake model only the influence from the first 90degrees of the trailed vorticity sheet is taken into account prescribed path only the trailed vorticity from the blade itself is considered HÁa Madsen and F Rasmussen (2004) A Near Wake Model for Trailing Vorticity Compared with the Blade Element Momentum Theory, Wind Energ. 2004; 7: (DOI: 26

27 Trailed vorticity modeling: Near wake model Trailed vorticity depends on the radial gradient of the bound circulation Most important At the blade root and tip Close to flaps 27

28 Induction from near wake and far wake model no tip correction model is used when the NW model is applied GR Pirrung, MH Hansen, HA Madsen (2012) Improvement of a near wake model for trailing vorticity. Presented at TORQUE 2012 in Oledenburg 28

29 Influence of trailed and shed vorticity on aerodynamic work Prescribed vibrations of the NREL 5 MW turbine at 8m/s wind speed first edge and first flap mode shapes have been used Out-of-plane In-plane Shed vorticity has influence along the whole blade Trailed vorticity is similarly important as shed vorticity at the blade tip 29

30 Influence of trailed vorticity on stability at overspeed Runaway case for NREL 5MW: No generator torque is applied Wind speed is slowly increased Shed vorticity included in dynamic stall model At some critical speed, flutter will occur and extract energy from the rotation Trailed vorticity increases the critical rotor speed by about 1 RPM 30

31 Stall Lift a = Attached flow a = Detached flow a = Stalled flow Angle of Attack, a 31

32 Dynamic stall and shed vorticity Shed vorticity effect Dynamic stall Both the dynamic stall and shed vorticity effect modelled in the Beddoes Leishman model 32

33 Dynamic stall and shed vorticity Both the dynamic stall and shed vorticity effect modelled in the Beddoes Leishman model 33

34 Influence of trailed and shed vorticity on aerodynamic work Prescribed vibrations of the NREL 5 MW turbine at 8m/s wind speed first edge and first flap mode shapes have been used Out-of-plane In-plane Shed vorticity has influence along the whole blade Trailed vorticity is similarly important as shed vorticity at the blade tip 34

35 Conclusions impact of model accuracy most pronounced at an operational point with low aerodynamic damping lack of modelling important flow phenomena like e.g. shed vorticity can in such cases have a considerable impact the increasing size of rotors and advanced control such as individual pitch control or flap control demands a supplement to the disc approach in the BEM theory like e.g. a nearwake model Thank you for your attention 35

36 Thank you for your attention 36