Croce, A.

Holling, M.

Messmer, T.

Montenegro Montero, M.

Peinke, J.

Yilmazlar, K.

English

Archivio istituzionale della ricerca - Politecnico di Milano

© ForWind @ForWind_DEEvolution of the wake of a floating wind turbine under imposed motion and mild turbulent conditions: a wind tunnel studyT Messmer1*, M Montenegro Montero2, K Yilmazlar2, A Croce2,  J Peinke1 and M Hölling11 ForWind - Center for Wind Energy Research, University of Oldenburg, Institute of Physics, 26129 Oldenburg, Germany2 Dept. of Aerospace Science and Technology, Politecnico di Milano, via La Masa 34, 20156 Milano, Italy*thomas.messmer@uni-oldenburg.deWESC 2023 Conference - Glasgow, 24/05/2023© ForWind @ForWind_DEWake of floating wind turbines❑ How these movements impact the wake?▪ Recovery▪ Transition to far-wake (gaussian profile)▪ Wake dynamics2❑ Motions of a FOWT▪ Wave driven (fp~0.1Hz)▪ Natural period in translation (fp~0.03 Hz)▪ Natural period in rotation (fp~0.01Hz)𝑈∞𝑆𝑡 =𝑓𝑝𝐷𝑈∞ 𝑓𝑝𝐷Roberston et al. (2014) Leimester et al. (2018)Schliffke et al. (2020)Li et al. (2022)𝑥© ForWind @ForWind_DEWind tunnel testing with a model FOWT❑ Model turbine Oldenburg 0.6 on a 6-DoF platform▪ Reproduce motions of a floating turbine▪ Wake measurements, 2D to 10D ▪ Hot-wires (1d in Oldenburg and 3d in Milan)3❑ Imposed 1DoF sinusoidal motions▪ Fixed▪ Sway with St ≈ 0.38, A~0.01D▪ Sway with St ≈ 0.38, A~0.01D▪ CT ≈ 0.85▪ U∞ ≈ 5 m/s -> Re ≈ 2.105𝑆𝑡 =𝑓𝑝𝐷𝑈∞SwaySurgeMessmer et al. (2022)© ForWind @ForWind_DEExperimental set-up4OldenburgMilanBackground TI∞ ≈ 1.5% Background TI∞ ≈ 0.3%YXZYXZ© ForWind @ForWind_DEWake speed and TI profiles at hub height (Milan, TI∞ ≈ 1.5 %)▪ Recovery starts x>4D▪ sway > surge > fixed▪ Shear layers merge at x=4D5© ForWind @ForWind_DEColor map of TI (Oldenburg, TI∞ ≈ 0.3 %)6© ForWind @ForWind_DEWake wind speed map (Milan, TI∞ ≈ 1.5 %)▪ Wake starts to recover at 4D▪ Integration of the average wind speed in rotor area-> recovery▪ Power available for a downstream turbine7© ForWind @ForWind_DERecovery vs. X/D (Oldenburg, TI∞ ≈ 0.3 %)8© ForWind @ForWind_DERecovery vs. X/D (Milan, TI∞ ≈ 1.5 %)9© ForWind @ForWind_DERecovery vs. X/D (Milan and Oldenburg)▪ Significant differences for fixed between TI∞ ≈ 0.3% and TI∞ ≈ 1.5 %▪ Effect of inflow turbulence seems more significant than movements▪ Nevertheless, motions enable faster recovery10© ForWind @ForWind_DEWhat are the mechanisms that play a role in the wake recovery process? 11© ForWind @ForWind_DEWake recovery rate equation▪ RANS equation in the streamwise direction▪ Tells about the exchange and transport of momentum within the wake12Transport through fluctuationsRate of pressure recoveryWake recovery rateTransport through mean flowX/D2 4 6 8 10 12Average over rotor00.1-0.1After Boudreau et al. (2017)© ForWind @ForWind_DEWake recovery rate (Oldenburg, TI∞ ≈ 0.3 %)13© ForWind @ForWind_DEWake recovery balance (Milan, TI∞ ≈ 1.5 %)14▪ Region of large variations: X/D in [3D, 7D]▪ Exch. of momentum driven by 𝜵 of turbulent fluctuations (Reynolds stresses), (𝜕𝑦 < 𝑣′𝑢′ >)/𝑈 and ), (𝜕𝑧 < 𝑢′𝑤′ >)/𝑈▪ Floating's turbine’s movements induce more wind speed fluctuations (small scale turbulence & coherent structures)© ForWind @ForWind_DEConclusion▪ Recovery up to 20% higher with motions in laminar (TI∞ ≈ 0.3%) wind compared to 7% with turbulence (TI∞ ≈ 1.5%)15▪ Motions accelerate transition to far-wake and enhance intensity of recovery▪ Induce larger wind speed fluctuations (Reynolds stresses)▪ Movements generate coherent flow structures in the wake▪ Strong dependency to St but also to A*▪ Further investigations needed on transition region and with different turbulent conditions© ForWind @ForWind_DE❑ Mailthomas.messmer@uni-oldenburg.de16❑ Websiteswww.forwind.de/www.floawer-h2020.eu/© ForWind @ForWind_DEAppendix17© ForWind @ForWind_DETypical motions of a 5MW FOWT❑ Results from openFASTsimulations▪ 3 floaters (OC4 Semi-sub, Spar, TLP)▪ Hs,Tp in ([1,6] m, [6,10] s)▪ Turbulent wind (U in [5,15] m/s)18❑ Analysis of motions show▪ Motions at floater’s natural frequencies, up to 15 m of amplitude▪ Motions at wave’s frequencies▪ Motions also driven by large turbulent eddiesOC4 DeepCwind semi-sub (Hs = 2.1 m, Tp = 8.8 s, U0 = 13 m/s) simulated with openFAST© ForWind @ForWind_DENREL 5MW FOWT → MoWiTO 0.6 FOWT 19ξ(t) = Ap.sin(2πfp.t)v(t) = dξ(t)/dt = 2π fp Ap.sin(2πfp.t)U(t) = U0 + v(t)ApU0fpUvApMoWiTO 0.6U0MoWiTO 0.6fpMoWiTO 0.6▪ λL = 217▪ λV = 1.5▪ λT = 145 ▪ ApMoWiTO 0.6 = Ap5MW / λL▪ fpMoWiTO 0.6 = λT x fp5MW▪ U0MoWiTO 0.6 = (λT / λL) x U05MWConserve among others▪ fred = fp x D / U0 = (D/U0) / (1/fp)▪ ΔCp▪ ΔCT© ForWind @ForWind_DEConservation of ΔCp20ξ(t) = Ap.sin(2πfp.t)v(t) = dξ(t)/dt = 2π fp Ap.sin(2πfp.t)U(t) = U0 + v(t)▪ ApMoWiTO 0.6 = Ap5MW / λL▪ fpMoWiTO 0.6 = λT x fp5MW▪ U0MoWiTO 0.6 = (λT / λL) x U05MWPower produced by a WT and power variation due to motionP(U, λ) = 0.5 ρ π R2 U3 Cp (λ) & ΔP = P(U0 + v, λ0 + λx) - P(U0, λ0)1st order Taylor developmentP(U0 + v, λ0 + λx) = P(U0, λ0) + dP/dU(U0,λ0) x v + dP/dλ(U0,λ0) x λxΔP = 0.5 ρ π R2 (3 U02) Cp(λ0) v + 0.5 ρ π R2 U03 dCp/dλ λx||ΔCP|| = 3 Cp ||v|| / U0 = 3 Cp 2π fp Ap / U0||ΔCP||5MW = 3 Cp 2π fp5MW Ap5MW / U05MW = 3 Cp 2π (λT x fpMoWiTO 0.6) . (ApMoWiTO 0.6 / λL) / ((λT / λL) x U0MoWiTO 0.6 )= ||ΔCP||MoWiTO 0.6

Evolution of the wake of a floating wind turbine under imposed motion and mild turbulent conditions: a wind tunnel study

https://re.public.polimi.it/bitstream/11311/1247278/1/MESST01-23.pdf

Evolution of the wake of a floating wind turbine under imposed motion and mild turbulent conditions: a wind tunnel study

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