Seminars

This study examines the flow structure of a 3D shock wave/boundary layer interaction induced by a swept compression ramp in a Mach 2 flow. The swept ramp has a streamwise compression corner angle of 22.5o and a sweep angle of 30o. A fluorescent-oil-flow technique is used to capture movies of the mean surface streaklines and stereo particle image velocimetry (PIV) is used to measure the three-component velocity field in a streamwise-transverse plane through the conical region of the interaction. PIV measurements close to the wind tunnel wall are enabled by using a windowed-ramp model that allows the laser sheet to propagate parallel to the wall and thus avoid laser glare. The surface flow visualisation movies very effectively reveal the mean separation line, reattachment line, transition to conical scaling, as well as the cross-flow and reverse-flow motions in the separated flow region. The mean velocity fields (u, v and w components) are consistent with the surface flow visualisation, and reveal reduced u in the separated flow region (between the mean separation line and reattachment), and large w in the direction of the cross-flow. The u-fields are in many ways similar to those observed in 2D compression ramp interactions. True reverse flow (negative u) is observed only in a small region close to the ramp corner over a transverse region of about 0.1 boundary layer thicknesses in height. The instantaneous velocity fields show a wide variation in separated flow size and an analysis was performed where the images were placed into bins of large or small separated flows and then ensemble averaged. These ensemble averaged fields reveal differences in the flow structure that are similar to what has been seen previously in 2D compression ramp interactions.