CFD simulations of wake effects at the Alpha VentusCFD simulations of wake effects at the Alpha VentusPO ID

CFD simulations of wake effects at the Alpha VentusPO ID

offshore Wind FarmPO. ID

offshore Wind Farmoffshore Wind Farm177 Annette Westerhellweg Thomas Neumann177 Annette Westerhellweg, Thomas Neumann

DEWI G bH Wilh l h G t h ll @d i dDEWI GmbH, Wilhelmshaven, Germany, a.westerhellweg @dewi.de, , y, g @

Abstract Results: Wind Speed Decrease in WakeAbstract Results: Wind Speed Decrease in Wake

Within the RAVE OWEA research project [1] measured wind turbine wake effects Wakes of nearest wt’s are metWithin the RAVE OWEA research project [1], measured wind turbine wake effects Wakes of nearest wt s are metll b th CFD d lat FINO1 have been compared with CFD simulation results. Wake effects are very well by the CFD modelat FINO1 have been compared with CFD simulation results. Wake effects are very

distinctively measurable at FINO1 in both forms: wind speed decrease andy

whereas the wake effects ofdistinctively measurable at FINO1 in both forms: wind speed decrease and whereas the wake effects ofturbulence intensity increase the wind turbines at largerturbulence intensity increase.A th i t t th t id f Al h V t ( it t FINO1)

the wind turbines at largerdi t ti t dAs there is no measurement at the east side of Alpha Ventus (opposite to FINO1), distances are overestimated.p ( pp ),

these effects can only be measured indirectly: The ambient wind speed can be The figures below show thethese effects can only be measured indirectly: The ambient wind speed can be The figures below show thei d d d fapproximated by a nacelle anemometer wind signal. The turbulence intensity wind speed decrease for aapproximated by a nacelle anemometer wind signal. The turbulence intensity

increase can only be determined by comparison with the general ambientp

free wind speed of 10m/sincrease can only be determined by comparison with the general ambient free wind speed of 10m/s,turbulence intensity Despite of the uncertainties of these methods it offers one of a 12m/s and 16m/sturbulence intensity. Despite of the uncertainties of these methods it offers one of af ibiliti f tit ti l ti f th k f t t f th t 5 MW

12m/s and 16m/s.few possibilities for a quantitative evaluation of the wake of state-of-the-art 5 MWp qwind turbineswind turbines.The measured wind speed reductions show high agreement with the CFDThe measured wind speed reductions show high agreement with the CFDsimulation results The turbulence increase was underestimated by the CFDsimulation results. The turbulence increase was underestimated by the CFDmodel The atmospheric stability has a measurable effect in the measurement of 10m/s 12m/s 16m/smodel. The atmospheric stability has a measurable effect in the measurement ofth i d diti i k U d t bl diti d i dthe wind conditions in wake. Under stable conditions a more pronounced windpspeed decrease is measured in the wake of the wind turbines of Alpha Ventusspeed decrease is measured in the wake of the wind turbines of Alpha Ventus.

Wi d F Al h V tWind Farm Alpha VentusWind Farm Alpha Ventus

Alpha Vent sAlpha Ventus:

Stability Dependency of Wind Speed Decrease• 6 Repower 5M with a rotor diameter of Stability Dependency of Wind Speed Decrease6 Repower 5M with a rotor diameter of126 (AV01 AV06)

y p y p126m (AV01-AV06) Wakes of the wind turbines adjacent to FINO1 are met best by the CFD simulationWakes of the wind turbines adjacent to FINO1 are met best by the CFD simulation

lt f t l diti D i t bl diti th d i d d• 6 AREVA M5000 with a rotor diameter results for neutral conditions. During stable conditions, the measured wind speed6 AREVA M5000 with a rotor diameterf 116 (AV07 AV12)

g , preduction is higher than the simulated reduction whereas during unstableof 116m (AV07-AV12). reduction is higher than the simulated reduction, whereas during unstable( )conditions the measured wind speed reduction is lower than the reduction

The measurement platform FINO1 isconditions the measured wind speed reduction is lower than the reductioni l t d ith th CFD d lThe measurement platform FINO1 is

l t d 405 t th t f i d t bisimulated with the CFD model.

located 405m to the west of wind turbineAV04 unstable neutal stableAV04. unstable neutal stable

CFD modelCFD model

Th CFD W k d lThe CFD Wake modeldeveloped in the OWID Results: Turbulence Increase in Wakedeveloped in the OWID

h j t [3] h thResults: Turbulence Increase in Wake

research project [3] has thep j [ ]following features: The turbulence intensity has beenfollowing features: The turbulence intensity has been

d f diff t bi t i db li RANS (R ld

assessed for different ambient wind• parabolic RANS (Reynolds- speeds and different stability classes Forp ( y

averaged Navier Stokes)speeds and different stability classes. For

averaged Navier-Stokes) unstable as well as for stableSolver

unstable as well as for stablestratifications the CFD simulationSolver stratifications, the CFD simulation

• CFD software Phoenics [4] underestimates the increase of the• CFD software Phoenics [4]. underestimates the increase of thet b l i t it i th i d t bi

k b l d lturbulence intensity in the wind turbine

• k-ε turbulence modely

wakeswakes.

• 10m Resolution• 10m Resolution

A t t Di M d l• Actuator Disc Model

stableneutalunstable

M t E l tiMeasurement EvaluationMeasurement Evaluation

Wind speed and wind direction data of FINO1,Wind speed and wind direction data of FINO1,91 5m LAT ha e been assessed A mast correction91.5m LAT have been assessed. A mast correctionof both data has been appliedof both data has been applied.D t f th ll t f t AV12 hData of the nacelle anemometer of wt AV12 havebeen used to estimate the undisturbed wind speed

Acknowledgementsbeen used to estimate the undisturbed wind speed.

Acknowledgements

This work is part of the research project RAVE-OWEA “Verification of Offshore-WEA” which is funded by thep p j yGerman Federal Ministry for the Environment Nature Conservation and Nuclear Safety (BMU) In particularGerman Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). In particularwe would like to thank Repower and AREVA for their supportwe would like to thank Repower and AREVA for their support.

Figure 3: Calibraton function to correct

R fFigure 3: Calibraton function to correctthe nacelle anemometer data of AV12 Referencesthe nacelle anemometer data of AV12to generate free wind speed data Referencesto generate free wind speed data

[1] RAVE: Research at Alpha Ventus www rave offshore deI h i d di ti t l th d t t h b l t d h ll [1] RAVE: Research at Alpha Ventus, www.rave-offshore.de.[2] V Ri d l T N RANS M d lli f Wi d Fl h h L Off h Wi d F P di f

In each wind direction sector only those data sets have been evaluated when all[2] V. Riedel, T. Neumann: RANS-Modelling of Wind Flow through Large Offshore Wind Farms, Proceedings of

ywind turbines in that sector were in full operation Depending on the data

the European Wind Energy Conference 2007, Mailand.wind turbines in that sector were in full operation. Depending on the data

il bili h l i i di id d i diff di ip gy ,

[3] T Neumann V Riedel K Grigutsch: Evaluation of Offshore Wind Design Parameter from FINO1-Dataavailability the evaluation is divided in different direction sectors: [3] T. Neumann, V. Riedel, K. Grigutsch: Evaluation of Offshore Wind Design Parameter from FINO1 Data(OWID Report) Proceedings DEWEK 2008 Bremen

y(OWID-Report), Proceedings DEWEK 2008, Bremen.

[4] Phoenics Software www cham co uk[4] Phoenics Software, www.cham.co.uk.C f Off[5] A. Westerhellweg, B. Canadillas, T. Neumann: Direction Dependency of Offshore Turbulence Intensity in

the German Bight. DEWEK 2010, Bremen.g ,[6] Launder B E Spalding D B : The numerical computation of turbulent flows Comp Meth In Appl Mech &[6] Launder, B.E., Spalding, D.B.: The numerical computation of turbulent flows, Comp. Meth. In Appl. Mech. &

Eng Vol 3 pp269 1974Eng., Vol.3, pp269, 1974.

EWEA 2011 Brussels Belgium: Europe’s Premier Wind Energy EventEWEA 2011, Brussels, Belgium: Europe s Premier Wind Energy Event.