18 March, Vienna Xia ojia n Hua ng, Cra nfie ld University, UK

Simula tion of VAW T for wa ke e ffects

Scope

• What we do? • Why we do? • What is available? • How we do? • What we learn? • What to do next?

W hat we do?

• Cranfield University • Energy and Power Engineering Division • Renewable Energy

• Wind, Wave & Tidal, Biomass, CCS • Wind

• VAWT(NOVA) • Offshore supporting structure(H2OCEAN) • Power system • Reliability models

W hy we do?

• Wake effects are important, many questions can be asked for VAWT

• Dynamic stall • Complex flow structure • Limited measurement

• Simulation

W hat is available?

• Desktop Computer • Core i5 4G RAM (Windows based)

• High Performance Computer(HPC) at Cranfield • Astral/Grid (Linux based)

• STAR-CCM+ v7.06.009 up to 32 processors • Measurements from NASA and Sandia National

Laboratory (SNL)

Two major tasks before solution

• Get the mesh setting right • How big can the model be?! For the 4G RAM

• 0.5G RAM per million cells for trimmer mesher • 2G RAM per million cells for polyhedral mesher

• Get the physics setting right • URANS + Turbulence models • General RAM requirement for solution

• 0.5G RAM per million cells for segregated solver • 1G RAM per million cells for explicit coupled solver • 2G RAM per million cells for implicit coupled solver

How we do?

• Start with simple cases! • Dynamic stall of airfoil

• Morphing(Deformed mesh) • VAWT simulation

• Rigid Body Motion

Oscillating a irfoil?

• 3 different regimes from NASA experiment • No stall : AOA=4+4sinωt; ω=2.199 • Light stall : AOA=11+4sinωt; ω=5.445 • Deep stall: AOA=17+5sinωt; ω=5.445 • Velocity 29m/s

Model setup

• No stall • Light stall • Deep stall

• Motion: morphing/rotation

No stall video (AOA=4°+4°sinωt)

Light sta ll video (AOA=11°+4°sinωt)

Deep sta ll video (AOA=17°+5°sinωt)

Oscillating a irfoil No sta ll ca se

0

0.1

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CL

Alpha(°)

No stall case-Alpha=4+4sin(2.199t)

NASA

K-O

Light stall case

0.6

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Alpha(°)

Light stall case-Alpha=11+4sin(5.445t)

NASA

k-epsilon

S-A

K-O

Deep stall case

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CL

Alpha(°)

Deep stall case-Alpha=17+5sin(5.445t)

NASA

K-epsilon

S-A

K-O

Rotating turbine

• Sandia-17m VAWT • Rotor Diameter=16.7m • Rated Power=100kw • Rotor speed=38.7 rpm • TSR=2.33 and TSR=4.60 • NACA0015

Local AOA (Low wind speed)

Local AOA (High wind speed)

Model setup

• Cell Number Count=~580000

• Viscous flow solved by implicit unsteady solver

• S-A turbulence model • Time step=0.0043s(to

ensure 360 time steps per revolution)

Simulation video(7.35m/s)

Simulation video(15.6m/s)

TSR=4.60 (Low wind speed)

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-90 -30 30 90 150 210 270

Nor

mal

forc

e co

effic

ient

Azimuth angle

Normal force coefficients(TSR=4.60)

Experimentaldata

STARCCM+2

TSR=2.33 (High wind speed)

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-90 -30 30 90 150 210 270

Nor

mal

forc

e co

effic

ient

Azimuth angle

Normal force coefficients(TSR=2.33)

Experimental data

StarCCM+

TSR=2.33 (High wind speed)

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-90 -30 30 90 150 210 270

Tang

entia

l for

ce c

oeffi

cien

t

Azimuth angle

Tangential force coefficients(TSR=2.33)

Experimental data

StarCCM+

W hat we learn?

• Simulation using STAR-CCM+ has given fair to good lift predictions for oscillating airfoil

• None of the turbulence models could account for all the regimes, S-A model gives better prediction in the deep stall case tested.

• Near wake simulation of rotating VAWT is validated under two different wind regimes, force predictions show acceptable agreement with the experimental data using S-A turbulence model.

W hat to do next?

• Mesh settings • Solver settings • Turbulence models • Far wake predictions • Co-simulation

Acknowledgement

• To Professor Feargal Brennan for his supervision and support

• To Andy Gittings for assistance in simulation on the HPC cluster

• To Michael Descamps from CD-adapco who kindly shared knowledge regarding morphing with me through email

Reference

• CD-adapco (2012) STAR-CCM+ User Guide 7.06 • Rhee, M. J. (2002). A study of dynamic stall vortex

development using two-dimensional data from the AFDD oscillating wing experiment (No. AFDD/TR-02-A-009). ARMY AVIATION RESEARCH AND TECHNOLOGY ACTIVITY MOFFETT FIELD CA AEROFLIGHTDYNAMICS DIRECTORATE.

• Paraschivoiu, I. (2002). Wind turbine design: with emphasis on Darrieus concept. Presses inter Polytechnique.

• Allet, A., & Paraschivoiu, I. (1995). Viscous flow and dynamic stall effects on vertical-axis wind turbines. International Journal of Rotating Machinery, 2(1), 1-14.

Thank you! Questions?