Control of flow separation and transition point over an aerofoil at low Re number using simultaneous blowing and suction

Abstract

Control of flow over a NACA2415 aerofoil which experiences a laminar separation bubble for a transitional Reynolds number of 2×105 is numerically simulated under the effects of blowing and suction. An earlier experimental study using hot-wire anemometry for a clean (no jet) NACA 2415 aerofoil at ? = 8° shows a laminar separation bubble over the one-third of the airfoil upper surface. In the no jet case, the recently developed k-kL-? and k-? SST transition models accurately predict the location and extent of the separation bubble. Later, single or multiple jets with a width of 2.5% the chord length are placed on the aerofoil upper surface for simulating the isolated or simultaneous blowing and suction jets. For single jets with blowing or suction, whereas the k-? SST model suppress the separation bubble in both cases, the k-kL-? transition model doesn't completely eliminate the separation bubble but moves it downstream in the suction case. Overall, the blowing/suction control mechanism appears to be suppression of the separation bubble and reduction of the upper surface pressure to increase the lift and decrease the drag. For simultaneous blowing and suction, firstly, a blowing jet at 10%c and a suction jet at 36%c are placed at the beginning and end of the separation bubble based on the best results of the single jets. Then, the locations of the blowing and suction jets are reversed. In both cases, both transition models eliminate the separation bubble resulting in increase in the lift and decrease in the drag. However, the best results in terms of the L/D ratios are still obtained with the single suction jets. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.