Embedded Imaging of Internal Shock Boundary Layer Interactions

Abstract

Ramjets and scramjets continue to be a central developmental focus spurred by both offensive and defensive needs on the battlefield. The development of field-able versions of these supersonic and hypersonic air-breathing propulsion systems will rely on improving the collective physical understanding of inlet flow physics enabled by the continued development of improved non-intrusive measurement systems. Present experimental methods of characterizing these internal, shock-dominated flows largely rely on the use of pressure taps in practical, optically-inaccessible geometries. The present work offers a solution in the form of a miniature embedded camera system which is designed to perform non-intrusive measurements which is then applied to the measurement of wall-bounded, incident/reflecting shock boundary layer interactions.

The camera system developed in this work leverages recent developments in the field of board-mounted camera systems to produce a packaged camera with integrated illumination which is capable of performing oil flow visualization (OFV) and pressure-sensitive paint (PSP) experiments. The system was fielded in the University of Tennessee Space Institute Mach 4.0 Ludwieg Tube, obtaining direct optical measurements at the throat of a custom-built Busemann streamline-traced inlet model. The camera system obtained pressure and shear fields while surviving the harsh tunnel environment. Following this initial success, the Auburn University variable Mach number tunnel was modified by adding an extension to enable the main experimental effort. The data from these tests suggest that corner flow/shock interaction is primarily driven by the swept shock interaction on the sidewall rather than Free-Interaction Theory (FIT). PSP and OFV results indicate that the corner region interaction length increases with Mach number, and decreases with wedge angle and shock strength. This trend is explained by comparison to the swept shock upstream interaction measurements of Settles and Lu. An interaction length scaling is proposed based on this work which acts synergistically with FIT to produce the scaled interaction.