Mean Flow Characterization of Swept Shock/Turbulent Boundary Layer Interactions Induced by an Impinging Oblique Shock

Abstract

Experiments have been conducted in a blowdown wind tunnel at Mach 2.1 and Mach 3.0 to study swept shock boundary layer interactions (SBLIs) generated by impinging, oblique shocks on a fully turbulent boundary layer. The overall goal of this work is to determine the effect of increasing the aspect ratio of the SBLI by comparing results to similar experiments conducted in a smaller wind tunnel. Shock sweep angles of 20 and 40 degree are tested at each Mach number. The quasi-infinite region is increased by increasing the aspect ratio of the shock generator from 2.33 in previous studies to 2.75 in the current study. To isolate the effect of sweep, a fixed inviscid pressure rise normal to the sweep angle of Cpn is used for each case. The mean flow topology is studied using three methods: infrared thermography, mean pressure measurements, and oil flow visualization. Mean flow results from each of the three techniques show good agreement and are able to identify salient features of the SBLI. The Stanton number distribution from infrared thermography accurately provides the location of the initial pressure rise and separation via a local minima and maxima in the Stanton number distribution. Mean pressure results also validate the locations of the initial pressure rise and separation locations determined from infrared thermography results. Oil flow shows the local skin friction direction on the SBLI surface and offers the most conclusive separation and reattachment locations, but also allows for the visualization of the initial pressure rise. The initial pressure rise and separation locations for all three methods align well, validating the use of infrared thermography to identify these salient features of the SBLI. A local maxima of the Stanton number distribution is seen in both separated and attached SBLIs. Therefore, heat flux data can be used to aid in determining the location of the separation for the SBLI, but does not offer conclusive results for whether the flow has separated or remains attached. Further, the Stanton number distribution is not sufficient in determining a precise location of reattachment if the flow has separated. Oil flow visualization offers the most conclusive results when determining separation and reattachment. Previous results from a smaller aspect ratio interaction show that separation exhibits conical similarity for 20 degree sweep in Mach 2.3 flow. However, oil flow visualization at Mach 2.1 for the larger aspect ratio interaction investigated here exhibits cylindrical behavior. This suggests that the SBLI aspect ratio influences the mean flow topology in that lower aspect ratios promote conical similarity. Comparison of the 40 degree sweep cases for the two different aspect ratio tests show similar structures, but Mach 3.0 results require further analysis since oil flow offers the most accurate reattachment location but was unable to be obtained for these tests.