Wind Turbine Wakes and Wind Farms. Stefan Ivanell Director, Stand Up for Wind Centre

Transcription

1 Wind Turbine Wakes and Wind Farms Stefan Ivanell Director, Stand Up for Wind Centre

2 Planning of lectures Lecture 1: Energy extraction and flow close to the blades Lecture 2: Flow behind the turbine, i.e., the wake 2(50)

3 Outline Lecture 1 Energy Extraction Boundary Layer Theory Blade Aerodynamics Power regulation Momentum Theory and Betz limit BEM Blade Element Momentum 3(50)

4 Wake Development: Near wake? Far wake 1. Vortex system formed from circulation 2. Roll-up into center vortex and distinct tip vortices 3. Destabilization of tip vortices : Turbulence 4. Break down into large-scale turbulence : Axial velocity intensity 5. Turbulent mixing 6. Interplay with meandering

5 Why do we need wake models? To determine performance of wind farms To estimate the life time of turbines in wind farms To operate optimally wind turbines in wind farms To optimize the location of wind turbines Factors influencing the wake: The distance between the turbines The stability of the atmospheric boundary layer

6 Increasing interest in wind turbine wakes Number of publications on the Web of Knowledge registered on the topic Wind Turbine Wakes

7 Wake Aerodynamics Full scale tests: Lidar measurements: Tjæreborg NM80, Risø Nordtank 500kW Wake deficits: Sexbierum, Vindeby, Nibe, Alsvik Park perfomance ( power deficits): Horns Rev, Lillgrund, Nysted, NoordZee, Nørrekær Enge Advantage: No restriction in model numbers Disadvantage: Difficult to measure and control

8 Wake Aerodynamics Wind/Water Tunnel tests: Wakes from a single turbine: NREL, Mexico, NTNU, Delft, ENSAM, IRPHE, Monash, DTU Wind farms: Univ. Minnesota, Johns Hopkins, Univ. Orleans, ECN Advantage: Easy to measure and control Disadvantage: Limitations in Reynolds numbers

9 Wake Structure

10 Wake Structure

11 Wake Structure

12 Vorticity S v v Rigid body rotation

13 Helmholtz Theorem Γmax Γmax Γmax

14 Circulation s 2 2D 3D Γ Γ 1 Γ 2 ds Γ 3 ds s 1 Γ

15 Helmholtz Theorem

16 Position Of Tip Vortex

17 Wake structure, wake instabilities and interaction Wakes of wind turbines at Horns Rev Wakes from first row survives longer than wakes inside park Wake breaks down due to instabilities of spiral vortices Wake vortices interact and roll up during breakdown process

18 Outlook Wind Energy - Backgound Background on going activities Wake structures, instabilities and interaction Numerical Methods Stability Study Farm Simulations Outlook Farm Farm interaction Summary and Conclusions

19 Background on wake simulations Analysis of numerically generated wake structures Wind Energy 12:1, 2009, Pages: Stability analysis of the tip vortices of a wind turbine Wind Energy 13:8, 2010, Pages:

20 20(41) Available Wake Measurement Data [Risø] DNW WT i Holland

21 Wake Aerodynamics CFD models Linearized Navier-Stokes Parabolised Navier-Stokes (Ainslie, UMPWAKE) Reynolds Averaged Navier-Stokes (RANS) Detached Eddy Simulation (DES) Large Eddy Simulation (LES) Actuator Disc/Line - LES (AD/L-LES) Remark: All models have their individual advantages and disadvantages!

22 Wake Aerodynamics Wakes computations: No. Mesh points CPU-time Comments PNS O(10**6) < 1h Both axisymm. and 3D AD-NS O(10**5) < 1h Polar coordinates RANS O(10**7) < 10h Steady DES O(10**8) < 1 week 3D-Unsteady AL-LES O(10**8) > 1 week Airfoil data required LES O(10**12) N/A 3D-unsteady

23 Scale requirements in wind energy Turbulent scales: Length scale (m) Velocity scale (m/s) Time scale (s) Airfoil boundary layer Airfoil Rotor Cluster Wind farm

24 Methods used EllipSys3D (Multi block, Finite volume, Collocated storage arrangement, MPI) The Actuator Line Method (ACL) or the Actuator Disc Method (ACD) LES (Mixed sub-grid-scale model by Ta Phuoc)

25 Actuator Line Method/Actuator Disc (DTU-Risø) Lift and drag forces from airfoil data applied along line No need to mesh blade, additional gridpoints in wake

26 Numerical Methods ACD/ACL Actuator Disc KTH Mechanics Actuator Line Lift and drag forces from airfoil data applied along line/disc No need to mesh blade, additional gridpoints in wake

27 Prescribed Wind Profile 27(41) y h hub Power law profile Parabolic profile Δ

28 With and without atmospheric turbulence

29 Velocity at hub height

30 Wake interaction 0 degree inflow angle 15 degree inflow angle

31 Pre-generated turbulent atmospheric boundary layer

32 Outlook Wind Energy - Backgound Background on going activities Wake structures, instabilities and interaction Numerical Methods Stability Study Farm Simulations Outlook Farm Farm interaction Summary and Conclusions

33 Stability of the tip vortices Apply time dependent forcing at the tip of blade to induce instabilities

34 Global mode using Fourier transform FFT of periodically excited flow Identify maximum of modes and follow growth in space First harmonic shows where NL effects starts 2

35 Instability mode: iso-contours of vorticity; St=0.33, 0.66 Sasan Sarmast

36 Apparent vortex roll-up and pairing

37 Unrolled wake out of phase oscillation for most unstable modes St=2 St=5 out-of phase oscillations lead to pinching, no clear roll-up/ pairing

38 Sarmast, Ivanell, Mikkelsen, Henningson et al.

39

40

41 Lillgrund NPC15, August 2012, Helsinki Horns rev Farm Simulations

42 Off shore Horns Rev 80 turbines with total capacity of 160MW Linné Centre Vestas V80-2.0MW turbines Rotor diameter: 80m Hub height: 70m Wind Farm Site Distance to coast: ~15 km Wind farm area: 20 km 2 Gotland University» 42(41)

43 Horns Rev 43(4

44 Horns Rev 44(4

45 Wake interaction model FLOW Conference 2012, Stefan Ivanell, 45

46 NPC15, August 2012, Helsinki Farm Simulations - 46 Example: wake losses at Lillgrund Denmark Sweden

47 Lillgrund (48 SWT-2.3 MW) 3.3 D 4.3 D NPC15, August 2012, Helsinki Farm Simulations

48 Wake losses (4.3xD) FLOW Conference 2012, Stefan Ivanell, 48

49 Wake losses (4.3xD) 1,2 [Jan-Åke Dahlberg] Relative power 1,0 0,8 0,6 0,4 Row_B_WD_219,1 Row_C_WD_219,0 Row_D_WD_219,1 0,2 0,0 Row_1 Row_2 Row_3 Row_4 Row_5 Row_6 Row_7 Row_8 Row_number FLOW Conference 2012, Stefan Ivanell, 49

50 Wake losses in row 1,3 and 5 (3.3xD) Row 1 Row 3 Row 5 FLOW Conference 2012, Stefan Ivanell, 50

51 Wake Losses CFD Simulation, Karl Nilsson [Jan-Åke Dahlberg] 1,2 Row 1 Relative power 1,0 Row 3 Row_1_WD_129,0 Row_3_WD_129,0 Row_5_WD_129,1 0,8 0,6 Row 5 Increased Production Decreased Loads 0,4 0,2 0,0 Row_A Row_B Row_C Row_D Row_E Row_number FLOW Conference 2012, Stefan Ivanell, 51 Row_F Row_G Row_H

52 Simulation results NPC15, August 2012, Helsinki Farm Simulations

53 Influence of ambient turbulence NPC15, August 2012, Helsinki Farm Simulations -

54 Derating of first row of turbines NPC15, August 2012, Helsinki Farm Simulations -

55 Wake length; TI = 0, 3.2, 4.7, 6.2 NPC15, August 2012, Helsinki Farm Simulations -

56 Farm-Farm interaction NPC15, August 2012, Helsinki Farm Farm Interaction - 56

57 Farm wake of Horns Rev [Sten Frandsen, Kurt Hansen et.al., The making of a 2nd generation wind farm model] NPC15, August 2012, Helsinki Farm Farm Interaction - 57

58 Measurements from Horns Rev NPC15, August 2012, Helsinki Farm Farm Interaction - 58

59 Technology Evolution National Renewable Energy Laboratory Innovation for Our Energy Future

60 Technology Development Today National Renewable Energy Laboratory Innovation for Our Energy Future 2.5 MW - typical commercial turbine Installation Boeing MW prototypes being installed for testing in Europe Most manufacturers have a 10 MW machine in design Large turbine development programs targeting offshore markets Weight constraints drive flexibility and aeroelastic coupling GE 3.6 MW; 111 m rotor

61 Summary

62 Wind Turbine Aerodynamics Stefan Ivanell Energy Extraction Ideal break up, Betz (1926) 2 V = V1 V2 = V 1 V 2/3V 1/3V V 62(34)

63 Wind Turbine Aerodynamics Stefan Ivanell Energy Extraction Power (kw) P (kw) Pmax (kw) Pturbine (kw) Vindspeed (m/s) 63(34)

64 Wind Turbine Aerodynamics Stefan Ivanell Boundary Layer Theory 64(50)

65 Wind Turbine Aerodynamics Stefan Ivanell Blade Aerodynamics 65(50)

66 Wind Turbine Aerodynamics Stefan Ivanell Blade Aerodynamics 66(34)

67 Wind Turbine Aerodynamics Stefan Ivanell Blade Aerodynamics 67(34)

68 Wind Turbine Aerodynamics Stefan Ivanell BEM 68(43)

69 Wind Turbine Aerodynamics Stefan Ivanell Helmholtz Theorem 69(34)

70 Wind Turbine Aerodynamics Stefan Ivanell With and without atmospheric turbulence 70(34)

71 Thank you for your attention! 71