The Influence of Turbulence Model on Wake Structure of TSTs when

used with a Coupled BEM-CFD Model

Ian Masters, R. Malki, Alison Williams & Nick Croft

Marine Energy Research GroupSwansea University

Modelling Approach

Source: A. Mason-Jones , PhD thesis Cardiff University (2010)

Moving Mesh Approach Time-averaged Approach

Array Modelling

Time-Averaged Influence of Blades

Discretisation of Turbine Blades

Discretisation of Turbine Blades (2)

Impact of Blades on the Flow

Impact of Blades on the Flow (2)

Calculating Resultant Forces

Resolving Forces

Calculating Source Terms (BEMT)

Substituting Source Terms (BEM-CFD)

Substituting Source Terms (BEM-CFD)

Model Domain

0.5m

0.25m

1.4m

0.5m

1.54m

0.84m

0.17m

0.84m

0.17m

Rotor Modelling

Wake Edge Parameters

Wake Edge Characterisation

95% Wake Edges

P∞

PWAKE

P95%

P∞

k-epsilon• Eddy viscosity from single length scale• Turbulent diffusion occurs only at specified scaleRNG k-epsilon• Account for different scales of motionk-omega• Viscous sub-layer flows• Adverse pressure gradients and separating flows

Turbulence Models

Shear Stress Transport (SST)• k-ω near boundary• k-ε in free-stream• Adverse pressure gradients & separating flowsReynolds Stress Model (RSM)• Reynolds Stresses directly computed• Directional effects of Reynolds stress fields• More suitable for anisotropic turbulence

Turbulence Models

Velocity

Velocity

Velocity

Turbulence Intensity

Turbulence Intensity

Turbulence Intensity

Turbulent Viscosity

Lateral Shear

Velocity ProfilesTSR = 4.0

Velocity ProfilesTSR = 4.0 & 6.0

TI ProfilesTSR = 4.0

TI ProfilesTSR = 4.0 & 6.0

Wake Diameter 95% Velocity

TSR = 4.0

Wake Diameter 95% Velocity

TSR = 4.0 & 6.0

Wake Diameter 95% TI

TSR = 4.0

Wake Diameter 95% TI

TSR = 4.0 & 6.0

Wake Diameter 95% dUdz TSR = 4.0

Wake Diameter 95% dUdz

TSR = 4.0 & 6.0

• Turbulence Models affect Hydrodynamics• Lack of Measured Data for Validation• Possibly better represent turbulence

Conclusions

Rotor Source Terms