Experimental investigation of primary and corner shock boundary layer interactions at mild back pressure ratios

Abstract

Unstart of rectangular inlets occurs as a result of interactions between shock-induced separation units along the floor/ceiling, corner, and sidewalls. While a significant body of literature exists regarding the individual flow interactions at the inlet floor/ceiling (called primary separation) and sidewalls, limited efforts have focused on the mean and dynamic features of the corner separation. Experiments are conducted to investigate primary and corner shock boundary layer interactions (SBLI) with the objectives of elucidating the flow interactions that occur in the corner, and characterizing the interaction between the corner and primary separation units at mild back pressure ratios. Surface streakline flow visualization and high-frequency wall static pressure measurements are performed along the centerline and corner regions of shock-induced flow separation generated by a 12° compression ramp in a Mach 2.5 flow. Sidewall fences that extend upstream of the leading edge of the flat plate generate corner separation of adequate size to determine the mean flow structures, characterize the unsteady motions, and investigate the mechanisms that drive the unsteadiness of primary and corner SBLI. Results show that the corner and primary SBLI units differ fundamentally in both their mean and unsteady features and their response to upstream and downstream flow perturbations. These observations suggest that the two behave as independent units at this relatively low shock-induced back pressure ratio.

Two-dimensional unsteadiness map of oblique shock wave/boundary layer interaction with sidewalls

“…None of the surface pressure correlations, consistently between the experiments and simulations, show any indication of a low-frequency unsteady connection between the sidewall and central separations. This is in agreement with the conclusion drawn from separate central and corner separation measurements by Funderburk & Narayanaswamy (2016). Due to the datasets only being available at the floor, it is not possible to directly assess the correlation of the two regions above the bottom wall on different wall-normal planes.…”

“…Experiments have an advantage in this sense if longer run times are available; however it is difficult to obtain high resolution spatial data over a sizeable extent. Funderburk & Narayanaswamy (2016) experimentally investigated this link by taking pressure measurements under the central and corner separations of a compression ramp SBLI. Noting the differences in the cross-coherences of the power spectra under the most energetic locations at the centre and corner with locations upstream and downstream of them, they concluded that the separations behave independently of each other.…”

Compression Ramp Induced Shock-Wave/Turbulent Boundary-Layer Interactions on a Compliant Material

“…The SBLI for each model is generated through three different compression ramps with angles of 16°, 20°, and 24°. The ramps were made of low-carbon steel and attached to each model using two screws through the pair of oval slots shown in another member in the research group, in a 3D SBLI configuration with compelling results [23] which allowed for a strong start to the investigation undertaken by this study. Images from these experiments had to be taken after the run when the model could be removed.…”

“…Figure 2.7 shows the set up for this form of measurement in the NCSU supersonic wind tunnel. This figureis adapted from Funderburk[22], and it should be noted that the model sidewall shown in the schematic are not present for this study. To provide a good contrast with the red pigment, all of the model surfaces were painted with a flat black background using a latex enamel spray paint from Krylon, Inc.…”

“…Schematic of set up for surface streakline visualization experiments.Figure adaptedfrom[22] The visualization procedure is as follows: The pigment-oil mixture is mixed and painted on the model in the area of interest before the run. During the run, this area is illuminated with the UV light source and recorded using a DSLR camera controlled on a PC remotely.…”