Modelling roughness effects for transitional low Reynolds number aerofoil flows

Roughness modelling at low Reynolds numbers of O(104–105) is of practical importance for micro air vehicles. This paper investigates the roughness modelling behaviour of the low Reynolds number shear stress transport model and the γ-Reθ shear stress transport model. Both include modelling flow transition and surface roughness effects. The roughness effects are modelled as sand grain roughness. A series of simulations using the two models have been performed on a NACA0012 aerofoil with comparisons to available experimental data. The results show that both of the models have the capability to reasonably predict the leading edge laminar separation bubble, transition and skin friction and, therefore, lift and drag on smooth surfaces. However, the two models behave very differently for the rough surface aerofoil. While the low Reynolds number shear stress transport model performs well, the γ-Reθ model fails to predict the transition on the rough aerofoil surface, resulting in inaccurate lift and drag prediction.