Passive Flow Control for Reduced Load Dynamics Aft of a Backward-Facing Step

Abstract

Passive flow control devices for a fully turbulent backward-facing step flow were investigated experimentally with particle image velocimetry and dynamic pressure transducers in the Trisonic Wind Tunnel Munich at Mach numbers of 0.80 and 2.00, as well as at Reynolds numbers of and 210,000, respectively. The results showed that these flow control devices, which are comprised of circular and square convoluted trailing edges on the backward-facing step, were a far more effective alternative to active flow control. The mean reattachment length was reduced by over 80% for the most effective configuration: so-called square lobes with a protrusion height of 0.4 step heights. This geometry also reduced the root mean square of the pressure fluctuations experienced by the reattachment surface by nearly 50% in transonic conditions. It was shown that the harmful step mode was weakened by forcing streamwise vorticity onto the flow through the presence of the lobes. The square lobes were more effective in diffusing this mode when compared to the circular lobes. Similarly, with increasing lobe sizes, the effectiveness of the flow control devices increased. Thus, a simple passive solution was determined for reducing the buffeting effects experienced by space launchers in transonic flight, for instance.