Performance of transition model for predicting low Re aerofoil flows without/with single and simultaneous blowing and suction

Abstract

Transition-sensitive, single point eddy viscosity models are fairly new and performance assessment of these models is required. In this study, the performance of transition and turbulence models is first evaluated for predicting low Re number flows having laminar separation bubbles that are traditionally quite difficult to predict for RANS-based CFD methods. Second, suppression of the laminar separation bubbles using blowing and/or suction is investigated for a single aerofoil. A prior experimental study using hot-wire anemometry for a clean (no jet) NACA 2415 aerofoil at alpha = 8 degrees at a Reynolds number of 2 x 10(5) shows the presence of a laminar separation bubble. For this flow, the recently developed k-k(L)-omega transition model is first shown to accurately predict the location and extent of the experimentally measured separation bubble. Following this, the same transition model was used to predict the flow over the NACA 2415 aerofoil using single or simultaneous blowing or suction. In the single blowing or suction cases, the separation bubble is not completely eliminated, but either abated or moved downstream. Smaller blowing velocity ratios cause more effective suppression of the separation bubble than larger blowing ratios, independent of the blowing locations. In contrast, larger suction velocity ratios are better than smaller suction ratios for the suppression. Moreover, the lift/drag ratios increase as the jet location moves from the leading edge to a downstream direction in both cases. In the simultaneous blowing and suction cases, the k-k(L)-omega transition model is shown to suppress the separation bubble by using a mix of jet parameters which result in increased lift/drag ratios. Crown Copyright (C) 2010 Published by Elsevier Masson SAS. All rights reserved.