Universitetet i Stavangeruis.no

CFD of wind wave interactionsSiri M. Kalvig

Forskningsnettverket for miljvennlig energi

27.09.2016

StormGeo and the Norwegian Research Council for financing

NORCOWE

Supervisor group:

Bjrn Hjertager (UiS) main supervisor

Jasna B. Jakobasen (UiS)

Eirik Manger (Acona Flow Technology)

Nina Winther-Kaland (StormGeo)

Master students:

Richard Kverneland (UiS)

Anne Mette Nodeland (NTNU)

Tommy Fredriksen (Telemark University College)

Acknowledgement

Motivation and research question

Numerical wave simulations

Numerical turbine simulations

Wind tunnel test

Wave influenced wind turbine simulations (WIWiTS)

Conclusions and future perspectives

Outline

Motivation

Site specific offshore forecast Headquarter forecast office

Model set up in StormGeo

ECMWF

ERA-Interim

80km / 3 hours

StormGeo in-housemodeling1-9 km / 1 hourSWAN

We need better link between wave models and atmospheric models!

Illustration: Silje Kalvig stdahl

Atmospheric stratification and wave effects are two major factors affecting wind conditions over sea versus land.

Photo: Lene Eliassen

A gap between best knowledge and best practise ?

Yes!

Neutral stratification and a flat, smooth sea surface

are routinely used as assumptions in wind energy calculations.

Will wave influenced wind at an offshore wind site result in different wind shear and more turbulence than expected ?

And if so, how will this affect the turbines?

Research question

Illustration: Silje Kalvig stdahl

Method forwind turbine performance

and wake modeling

Testing, numerical experiments, produce

results

Summarize and conclude the PhD work

Couple the methods

Literature study, clarify the relevance for the PhD work

On wave-wind interactions and implications for offshore wind turbine

Testing, numerical experiments, produce

results

Method forwave influenced wind

simulations

Testing, numerical experiments, produce

results

From: Grand Valley State University

Need a new boundary condition that take into account the sinusoidal movement of the ground.

Numerical wave simulations

Different waves canbe superposed oneachother

, = 2(

) + 2(

)

is the total wave surface displacement, and are a unitvectors, x is the horizontal position at a given time t, a is the waveamplitude, is the wavelength and c is the wave speed.

Domain: 1200m x 25 m x 400 m, Logarithmic wind at inlet with U400m =8 m/s, z0=0.0002 m. Profiles are sampled from the middle of the domain (x=600 m) for every second between 251-300 seconds of simulations

Numerical wave simulations

wind aligned with wavewind oppose wavewithout wave

wind aligned with wavewind oppose wavewithout wave

Wave with a = 4 m, L = 50 m, c = 8.8 m/s Wave with a = 4 m, L = 100 m, c = 12.5 m/s

Domain: 1200m x 25 m x 400 m, Logarithmic wind at inlet with U400m =8 m/s, z0=0.0002 m. Profiles are sampled from the middle of the domain (x=600 m) for every second between 251-300 seconds of simulations

Numerical wave simulations

wind aligned with wavewind oppose wave

wind aligned with wavewind oppose wave

Wave with a = 4 m, L = 50 m, c = 8.8 m/s Wave with a = 4 m, L = 100 m, c = 12.5 m/s

Domain: 1200m x 25 m x 400 m, Logarithmic wind at inlet with U400m =8 m/s, z0=0.0002 m. Profiles are sampled from the middle of the domain (x=600 m) for every second between 251-300 seconds of simulations

Numerical wave simulations

wind aligned with wavewind oppose wave

wind aligned with wavewind oppose wave

Wave with a = 4 m, L = 50 m, c = 8.8 m/s Wave with a = 4 m, L = 100 m, c = 12.5 m/s

LES

URANS

Test with data from the NORCOWE & NOWITECH wind tunnel blind test.

Numerical turbine simulations

Testing of wind turbine models

Actuator disk model: openFOAMSteady state (simpleWindFoam)RANS, k-epsilon model1.7 million cells

Fully resolved method: ANSYS/FluentDone by Eirik Manger, Acona Flow technologyTransientRANS, k-omega model5.3 million cells

Actuator Line model: openFOAMTransient (pisoFoamTurbine)URANS, k-epsilon model2.4 million cells

Actuator line method in SOWFA

Actuator line method of Srensen and Shen1 used in the Simulator for Offshore Wind Farm Applications SOWFA2.

Manger and Kalvig visiting NREL, Boulder

1Srensen, J. N., & Shen, W. Z. (2002). Numerical modeling of wind turbine wakes. Journal of Fluids Engineering2Churchfield MJ, Lee S and Moriarty P 2012 Overview of the simulator for offshore wind farm application (SOWFA) National

Renewable Energy Laboratory, Golden, CO, USA 03 May 2012

Actuator line method, wind tunnel test

Waves + Actuator Line (SOWFA) FAST

Wave simulations are combined with the actuator line simulations of SOWFA and coupled with FAST. New set up: Wave Influenced Wind Turbine Simulations (WIWiTS)

New Method for direct study of:Wave Influenced Wind Turbine Simulations

WIWiTS

WIWiTS Using the NREL 5 MW turbine, reference turbine (hub height 90 m, rotor diameter 126 m)

WIWiTS

WIWiTS domain with wave aligned (left) with the wind direction and wave opposing the wind direction (right). The color contours showing the wind velocity in the x-direction.

WIWiTS

Generated rotor power per density (Wm3/kg) for the three different cases; wind and swell in the same direction (blue), wind and swell in the opposite direction (red) and wind over a surface with low roughness (black). L=100 m, a=4 m, c=12,5 m/s

wind aligned with wavewind oppose wavewithout wave

Inlet wind U400= 8m/s

WIWiTS with FAST

Stress at the blade root due to the flapwise bending moment at the blade root.Fatigue calculations by Lene Eliassen at NTNU.

Conclusions New method for wave induced wind simulations

The flow response over the waves is very different compared with flow over a flat sea surface.

Wave direction relative to wind direction important.

The swept wind turbine rotor area will be exposed to wind profiles and turbulent levels other than what is predicted with the usual assumption of a logarithmic wind profile and low turbulence levels over a flat surface.

URANS can serve as a good substitute to the more computational requiring LES for Actuator line (SOWFA) simulations.

The actuator line in SOWFA slightly improved (more robust)

Actuator line in URANS mode predict reasonably well both turbine performance and the turbine wake.

Conclusions

A new tool: Wave influenced wind turbine simulations WIWiTS.

Simulations with WIWiTS showed that swell will affect the power output. Oscillation in power had the same frequency as the waves. The opposed case gave slightly larger power output than the aligned case.

Simulations with WIWiTS coupled to FAST demonstrated that wave influenced wind increases the fatigue damage compared to a situation with no waves, especially for the cases where the wave field opposes the wind field.

Future perspectives

Further improvements of WIWiTS

WIWiTS with the FAST mode activated needs further validation and testing.

Only bottom fixed horizontal axis turbines are studied here. It would be interesting to extend the method to include vertical axis turbines and floating concepts.

Investigations on how knowledge from idealized CFD studies of wind wave effects can be incorporated in operational mesoscale models will also be an important area to explore.

Research Network for Sustainable Energy

Administration

Board

Energyefficiency

Renewabletechnology

Transition CCUS Smart cities

Mohsen Assadi Bjrn Hjertager Oluf Langhelle Ying Guo Chunming Rong

Future initiatives motivated from NORCOWE participation

Uis together with MARINTEK withsupport from:Statoil, Kongsberg, Fugro, NREL, Vestas, Von Karman Institute

WoW Project

Challenge:How can we model the effect the waves have on the MABL? And will the wave effect be significant for a the performance of a wind turbine?

Solutions:The dynamical behavior of the waves can be model be the use of a moving mesh approach in CFD and the wind turbine can be modeled by the actuator line method already developed in NRELs SOWFA.

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https://vimeo.com/164625203

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CFD of wind wave interactionsSlide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19WIWiTSWIWiTSWIWiTS with FASTSlide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Offgrid energy solution for fishfarmingMiljvennlig energy til fiskeoppdrettSlide Number 29Slide Number 30Floating VAWT, cost/benefit, upscalingWind energy in cold marine climateSlide Number 33Slide Number 34