The Science of Making Torque from Wind

Transcription

1 The Science of Making Torque from Wind Oldenburg October 9-11, 2012 Recent advances in aeroelasticity of wind turbines Spyros Voutsinas NTUA, School of Mechanical Engineering

2 Outline 1. Aeroelasticity: Needs & Issues 2. Tools 3. Selected applications / problems Large flexible blades Stand-still operation Load reduction through control Passive instability suppression (bent/torsion coupling) Deformable TE flaps Pre-bent & swept blades 4. Outlook 2/total

3 Aeroelasticity: needs & issues Needs: Issues: Accurately reproduce the life-time of a wind turbine Assure safety à keep track of loads Reduce kwh cost à reduce loads Ø Involve a long list of load cases (IEC standard) Ø Require modeling of complex coupled phenomena Ø Updates needed to account for technology progress Run-cost of a design cycle & problem complexity Ø Simplified assumptions are needed Accuracy of modeling & associated uncertainty Ø Difficult to assess (lack of appropriate measurements) The agenda of problems is fast evolving & challenging Ø Size increase & flexibility Ø Deep offshore 3/total

4 State-of-art & research tools The basic layout Integrator Dynamics: Multi-body Structure: 1 st order beam Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling Control Passive: flow + structure Active: power + loads 4/total

5 State-of-art & research tools The basic layout Integrator Dynamics: Multi-body Structure: 1 st order beam Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling 2 nd order beam theory (DTU,NTUA) non-linear effects (complex laminates & sandwish skins UP) Control Passive: flow + structure Active: power + loads 5/total

6 State-of-art & research tools The basic layout Integrator Dynamics: Multi-body Structure: 1 st order beam Sub-body models (e.g. GAST (NTUA), HACW2 (DTU)) Loads major body Aerodynamics: BEM (+add on s) receives rotations and translations Hydrodynamics: Wave theory Moorings: line modeling ζ sub-body A(q) η ζ y η Control Passive: flow + structure Active: power + loads ρ(q) ξ communicates loads to the previous sub-body ξ x 6/total

7 State-of-art & research tools The basic layout Integrator Dynamics: Multi-body Structure: 1 st order beam Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling Control Passive: flow + structure Active: power + loads BEM_based models are exclusively used in design. Their accuracy varies depending on the flow conditions. There are doubts that have not and cannot be dealt decisively and for good. Other alternatives: Vortex methods: Lifting L [+CFD] (DTU), Free-wake panel (Ustutt, TUDelft), Vortex particles (NTUA) Vortex + boundary layer NTUA (Foil2w), ECN (Rfoil), DTU (q3uic) CFD 7/total

8 State-of-art & research tools The basic layout Hybrid wake Integrator Dynamics: Multi-body Structure: 1 st order beam 1D (a) Near wake Medium wake Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling i,j,k (b) Control Passive: flow + structure Active: power + loads 60 min simulations are made possible (c) 8/total

9 State-of-art & research tools The basic layout Integrator Dynamics: Multi-body Structure: 1 st order beam Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling Control Passive: flow + structure Active: power + loads Aeroelastic stability and control Linearized models (state space representation) Frequency & damping of WT systems in closed loop operation (e.g. HACWstab (DTU) and GAST (NTUA)) 9/total

10 State-of-art & research tools Integrator Dynamics: Multi-body Structure: 1 st order beam Loads Aerodynamics: BEM (+add on s) Hydrodynamics: Wave theory Moorings: line modeling Control Passive: flow + structure Active: power + loads 1st backward lead-lag mode 1st forward lead-lag mode damping in log decrement (%) damping in log decrement (% ) meas Non-linear linear wind speed (m/s) wind speed (m/s) 10/total

11 Non-linear effects due to large deflections Uniform inflow 11 m/s (near rated operation) - loads Large flexible blades Increase in amplitude of variation of the flapping moment and torsion. Especially for torsion significantly higher dynamic loads are obtained 11/total

12 Large flexible blades flap/torsion coupling z ζ M ζ M z η M y w x ξ y Almost negligible effect on flapwise deflections Large effect on torsion angle variation The effect on torsion becomes more pronounced when large flapwise deflections occur 12/total

13 Large flexible blades Effect of the geometrical non-linearities on stability of the NREL 5MW WT Freq shift 2 nd order beam modeling Damping can be reduced by half the 1 st edgewise mode Kallesoe, 2011, (Risoe-DTU) 13/total

14 Stand-still operation The underlying mechanism: Issue: Tools: Vortex Induced Vibrations Stability some type of CFD Du96-w-180: Skrzypiński et al, DTU /total

15 Stand-still response Definitely CFD gives in depth insight to the problem but is expensive VII modeling is by far less expensive but also less interpretable 15/total

16 Stand-still response Mean values match well Signal processing provides the shedding frequencies 16/total

17 Forced vibrations gives insight in the eventual lock-in Stand-still response Load-displacement plots for A*/T*= /total

18 Stand-still response Elastic suspension (aeroelastic problem for a typical airfoil) gives information on stability (results with and without structural damping) 18/total

19 Load reduction through control As wind turbines became bigger, use of control was extended to load reduction. The primary tool is pitch, but other means (e.g. flaps) are being studied. Pitch can be time varying or cyclic Load reduction via control plays a very important role in offshore for substructure load/motion reduction 19/total

20 Load reduction through control PSD of tower nodding base moment [(knm) 2 ] 10 8 baseline collnod no limit Active control of tower vibrations through collective pitch of the blades tower nodding base moment PSD of tower nodding base moment [(knm) 2 ] baseline collnod filter frequency [Hz] Leq/Leq_base collnod_no_lim collnod collnod_filter_1 collnod_filter_2 collnod_filter_3 ntm 14 etm 14 ntm 18 ltm frequency [Hz] 20/total

21 Load reduction through control POLIMI EWEC 2012 Combined BTC(Bending torsion coupling) and IPC (individual pitch control) 21/total

22 Deformable TE TE flaps aim at reducing loads by changing the aerodynamics Modeling challenges: some kind of CFD is again needed CFD can provide insight & help the calibration of engineering models [modeling: DTU, NTUA; tests: TUDelft, DTU] L U wind D α wind NACA /total

23 Deformable TE 0.6 K I = 0 K I = K I = 0 K I = 1 Flap deformation Flapwise TE angle Flap Angle Reduced Time Reduced Time CL C L Inactive flap Flap Ki=1 K I = 0 K I = Reduced Time Xsep X sep a effective K I = 0 K I = 1 Response to a sinusoidal wind with α 0 = 14 o,α 1 = 2 o και ω = /total

24 Deformable TE Garcia (DTU) Foil2w (NTUA) Validation of viscous inviscid interaction models 24/total

25 the 3D model In case of TE flap deflection, the vorticity emission scheme has been modified in order to take into account the tip vortices at the extremities of the flap blade blade flap flap Γ b Γ f Γ f -Γ b detached emission continuous emission 25/total

26 Results: the 3D case Effect of the span wise length (11m/s) 6 tip flapwise displacement (m) inactive TE flap width = 10m flap width = 20m flap width = 30m TE flap deflection [deg] inactive TE flap width = 10m flap width = 20m flap width = 30m root flap bending moment (10 6 Ntm) time (s) time (s) inactive TE flap width = 10m flap width = 20m flap width = 30m time (s) 5MW RWT, Shear exp 0.2 The spanwise length has small effect The reduction of the load is 30-35% 26/total

27 Pre-bent & swept blades z e r r r r 0 = a tip 0 b a = 3m b= 2 a = 3m b= 4 sweep geometry defined in UPWIND project different tip offsets ranging from 1m-6m are analyzed Original airfoils not placed normal to deflected elastic axis 27/total

28 inboard vortices shed ahead of the tip ones inducing up-wash towards the tip aerodynamic analysis of the deformed blade geometry non linear aeroelastic coupling GENUVP vortex particles code 28/total

29 Pre-bent & swept blades GAST GENUVP Increase of loading towards the tip Lower loads in more inboard sections U=8 m/s, b=2 29/total

30 Pre-bent & swept blades Penalty in Power Production Equivalent Load blade root flaping moment BEM (%) GENUVP (%) a=0, b=0 0 0 a=6, b= a=6, b= a=6, b= a=6, b= spline Risø-DTU analysis 30/total

31 Pre-bent & swept blades flapwise flapwise deflection deflection at at blade blade tip tip [m] [m] no bend fore 1.5 aft 1.5 torsion angle at blade tip [deg] no bend fore 1.5 aft 1.5 U=11 m/s aft pre-bend blade t t [s] [s] t [s] flapwise bending flapwise moment deflection at blade at root blade [Nm] tip [m] flapwise deflection at blade tip [m] E E E E E t [s] t [s] 7.5E+06 no nobend fore fore aft aft RISOE no bend ECN CRES/NTUA RISOE fore 1.5 ECN CRES/NTUA RISOE aft 1.5 ECN CRES/NTUA torsion moment torsion at angle blade at root blade [Nm] tip [deg] torsion angle at blade tip [deg] t [s] t [s] t [s] t [s] RISOE no no bend bend ECN ECN no nobend fore fore aft 4.5 RISOE no bend aft ECN4.5 CRES/NTUA RISOE fore 1.5 ECN CRES/NTUA RISOE aft 1.5 ECN CRES/NTUA RISOE no no bend bend ECN ECN edgewise instabilities induced by high aft pre-bend 31/total

32 Concluding remarks & Outlook Aeroelasticity [hydro-servo-aero-elasticity] is by definition a interdisciplinary topic including a variety of challenging engineering problems. There has been a lot of progress in aeroelasticity that allow good simulation of the whole wind turbine system in fully coupled mode Further progress is needed in several aspects: In terms of modeling Aerodynamics: calibration of BEM with respect to new concepts assessment of accuracy & uncertainties in aerodynamic modeling Structural modeling: non-linear modeling (high flexibility & structural tailoring) Reduced order modeling: related to run-cost reduction and control Hydrodynamics: non-linear wave loading analysis & extreme wave conditions In terms of design (and also modeling): Aerodynamic & hydrodynamic accessories: flaps, VGs System identification & control design 32/total