Tim Fletcher (presenter)Post-doctoral Research Assistant

DaHye KimPostgraduate Research Student

Oh Joon KwonProfessor

Richard BrownMechan Chair of Engineering

Rotor Aeromechanics Laboratory Glasgow University

Computational Aerodynamics Laboratory KAIST

Predicting Wind Turbine Blade Loads usingVorticity Transport and RANS Methodologies

European Wind Energy Conference16-19th March 2009

Vorticity Transport and RANS Models

• Solves unsteady vorticity transport equation:

• Lifting-line blade aerodynamic model, trailed and shed vorticity is accounted for using the source term, S

• Numerical diffusion of vorticity is limited by using a weighted average flux method – wake structure is preserved

• Solved in finite-volume form on a structured Cartesian mesh

ωνSuωωuωt

2

Vorticity Transport Model RANS

• Reynolds-Averaged Navier-Stokes equations are solved in finite volume form on a hybrid grid

• Flow assumed fully turbulent – Spalart-Allmaras model used

• Inviscid flux terms are solved by flux-difference splitting; viscous terms by a central-difference method

• Simulations are steady, mostly using one blade with periodic boundary conditions

European Wind Energy Conference16-19th March 2009

Blade Aerodynamic Loading

Wind: 7 m/s

Wind Turbine Model:

NREL Phase VI rotor

• Rigid

• 2 blades

• Radius 5.029m

• S809 aerofoil

• Rotor speed 72rpm (constant)

• Blade pitch 3°

Normal Force Coefficient, Cn

Tangential Force Coefficient, Ct

r/R

r/R

European Wind Energy Conference16-19th March 2009

Blade Aerodynamic Loading

Wind: 10 m/s

Wind: 25 m/s

r/R r/R

r/R r/R

Cn Cn

CtCt

European Wind Energy Conference16-19th March 2009

Distribution of Pressure Coefficient

Wind: 10 m/s

Wind: 25 m/s

European Wind Energy Conference16-19th March 2009

Suction Surface Streamlines

European Wind Energy Conference16-19th March 2009

Wake Structure

VTM

RANS

Vortex Age [deg]

Axial Location

(z/R)

Radial Location (r/R)

Rotor

European Wind Energy Conference16-19th March 2009

Conclusion

• VTM can be run using coarse aerodynamic discretisation to give efficient performance predictions

• VTM simulations using a finer discretisation of the wake have revealed the subtle characteristics of the vortex filaments and the changes in wake structure that result from natural vortex instability

• RANS provides accurate predictions of the aerodynamic loading on the blades, and the velocity and pressures fields that surround them. The computational cost is high, though.

• In the short term: the VTM and RANS methods can be used to inform the results provided by each other

• In the longer term: improvements in computational resources may allow hybrid VTM-RANS schemes to be used