Control of forced shock-wave oscillations and separated boundary layer interaction

The purpose of the present study is to analyze the unsteady aspects of the transonic interaction between an oscillating shock-wave and a separated boundary layer in a channel flow. Oscillation of the shock-wave is forced thanks to a periodic variation of the downstream throat section given by a rotating elliptical shaft located near this throat, in the middle of the channel, inducing pressure perturbations moving upstream. The channelʹs lower wall is equipped with a contour profile – or a bump – allowing for flow separation. Flow field visualizations during a shock-wave oscillation cycle have been carried out using a continuous light system coupled with a high-speed camera and a spark light system coupled with a drum camera. Continuous and unsteady wall pressure measurements have been conducted. Spectral analysis of the signals has shown that response from sensors is driven by the leading shock oscillation of the λ-shock structure and also has allowed for the phase velocity of the downstream perturbations to be determined. Two-component laser Doppler velocimetry probings have been carried out and phase-averaged fields obtained thanks to a time information given by a marker located on the rotating shaft. The evolution of the separated bubble during a shock-wave oscillation period has been accurately quantified. The impact of control techniques – passive and active by suction – on the boundary layer and on the forced oscillation of the shock-wave has been characterized. The control device is a cavity covered by a perforated plate located in the interaction region. Active control has decreased the shock oscillation amplitude thanks to the suction of the separated boundary layer across the perforated plate.