Relative assessment of different turbulence models in prediction of airfoil characteristics for a wide range of angle of attack

Abstract

Simulation of separated flow past an airfoil beyond stall, along with the prediction of stall itself still remains a challenging problem. In practical design and analysis problems of aerodynamics involving turbulent flow, the most widely used methodology is the numerical solution of the Reynolds Averaged Navier Stokes (RANS) in conjunction with appropriate closure models to represent the effect of turbulent stresses. The present paper attempts to compute flow past a symmetric airfoil for a wide range of angles of attack using the code RANS3D developed at NAL Bangalore. The RANS code is coupled to three different eddy viscosity based turbulence models - viz., the low Re version of the k - E model, low Re version of k-w model and the v2 - f model, for which the ability to capture the massive flow separation at and beyond stall has been carefully examined for an operating chord-based Reynolds number of 2 to 3 million and the angle of attack varying from 0 to 25 degrees. Validation against measurement data for instantaneous flow field indicate that all the turbulence models perform almost equally well in pre-stall regimes, while some uncertainties are observed when the flow becomes highly unsteady for high angle of attack. The vortex shedding from the upper surface of the airfoil leading to massive separated flow structure is captured by all the turbulence models. As far as the mean lift and drag coefficients are concerned, reasonable agreement is observed between the low Re k-E low Re k-w model prediction and the measurement data whereas the v2 - f model, in general, has a tendency of overpredicting the aerodynamic coefficients. The Strouhal number, indicating the frequency of the periodic vortex shedding behavior, is observed to be not so sensitive to the turbulence model used for computation