Aerodynamic design of a wind turbine diffuser with openfoam

Abstract eng:
The extractable energy of an horizontal-axis wind turbine rotor of fixed size can be increased by installing it inside of a diffuser. The diffuser helps to reduced the pressure behind the turbine compared to a bare turbine. The flow separation in the diffuser, also called diffuser stall, is one of the main problems concerning power extraction as it limits the area expansion. It depends mainly on the diffuser inlet conditions, exit conditions, Reynolds number, Mach number, and diffuser geometry. The aim of this work is to study the influence of wall functions and turbulence models used on the design of a diffuser augmented wind turbine (DAWT). A baseline configuration of maximum pressure loss at the actuator disk and area expansion, without flow detachment have been selected based on previous studies [14]. This 2D model with an expansion area µ = Aext /At = 3.7, included angle δ = 19.6o , pressure loss at the disk of k pc = 0.36 and at the diffuser k pd = 0.18 generates a pressure coefficient at the diffuser exit c pex = −0.75. Steady simulations have been performed using different incompressible turbulence models Launder-Sharma k − ε (LSke), Spalart–Allmaras (SA), k − ωSST (kwSST) and v2 − f (v2f). The geometry was generated with Salome, meshed with snappyHexMesh and the problem was numerically solved with OpenFOAM.

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