Experimental Investigation of Turbulent Flow Past a Backward Facing Step with Air Blowing in Bottom Corner

Abstract

The mean flow properties of separated flow at a backward-facing step bottom corner variable blowing has been investigated experimentally. The Reynolds number based on freestream velocity U &#61 40m/s and step height h &#61 40 mm was 1.1 x 10 up 6, and the incoming boundary layer at the separation point was fully turbulent. The momentum thickness Reynolds number was R &#61 2490 and thickness delta &#61 1.1 cm. In the experiment conventional pressure measurement and flow visualization techniques have been used. In addition, a new designed double- direction pitot probe was used successfully in the experiment to study the reverse flow. A reverse flow factor gamma n based on the new probe was proposed and used to describe the behaviour of the reverse flow region. Five different heights of the air blowing slot were used during the experiment, with ratios of h/H &#61 0.0, 0.04375, 0.0875, 0.13125 and 0.175 respectively. The experiment indicated thatthe flow separation region becomes increasingly affected by bottom corner blowing. The area of flow recirculation is gradually reduced with increased blowing. As soon as the blowing slot h/H greater than 0.0875 the reverse flow fully disappears on step downstream surface.