Leon Vanstone

Effect of Upstream Boundary Layer on Unsteadiness of Swept-Ramp Shock/Boundary Layer Interactions at Mach 2

This study further examines the flow structure and unsteadiness of a 3D shock-wave boundary-layer interaction (SWBLI) generated from a swept compression ramp in a Mach 2 flow using particle image velocimetry (PIV) and high-speed planar laser scattering (PLS). The ramp has a streamwise angle of 22.5 and a swept angle of 30. A preliminary investigation has already been conducted using a fluorescent-oil-flow technique and 5 Hz PIV at a single spanwise location through the conical region of the interaction. This study continues to investigate this mechanism. Low repetition rate (5 Hz), high-resolution (2k x 2k) PIV is conducted in the x-z plane, which is supported by high-speed (10 kHz) PLS using an alcohol fog as the scattering medium. It is observed that the instantaneous separation line is highly undulated and appears to be correlated to large streamwise fluctuations in the upstream boundary layer (superstructures). These superstructures are observed in the upstream boundary layer (as in previous studies) and act to shrink or grow the local separation region that they impinge upon. Large-scale unsteadiness mechanisms for the separation line were also investigated. The bulk motion of the separation line is also shown to be effected by momentum in the boundary layer. In essence, correlations are observed both smalland largescale that link the separation-line location with the momentum in the boundary layer.

Experimental Investigation of Unsteadiness of Swept-Ramp Shock/Boundary Layer Interactions at Mach 2

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 22.5 and a sweep angle of 30. 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 streamwisetransverse 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.

Closed-Loop Control of Shock-Train Location in a Combusting Scramjet

This study demonstrates the closed-loop control of a shock-train location in the isolator of a Mach 2.2 direct-connect dual-mode scramjet facility (U.S. Air Force Research Laboratory research cell ...