Experimental analysis of the impact of an acoustic excitation on a separated boundary layer behaviour

Abstract The paper examines the effect of acoustic excitation at broadband frequency range (100 - 650 Hz) on separated boundary layer developing on a flat plate subjected to an adverse pressure gradient. The experiment was conducted with a low inlet turbulence intensity level (Tu < 1%) in order to provide a cleaner environment that magnifies the effects of the excitation frequency. It was shown that acoustic excitation at sound pressure levels: SPL=125 and 135 dB, can lead to a more rapid increase in flow instability followed by an earlier laminar-turbulent (l-t) transition. The boundary layer reattachment point was shifted upstream and the size of the separation bubble was reduced in the flow with the acoustic excitation active.