Effects of Surface Compliance on Shock Boundary Layer Interaction in the Caltech Mach 4 Ludwieg Tube

Abstract

Understanding the effects of fluid-structure interactions caused by turbulent boundary layers and shock boundary layer interactions, on thin, compliant, structures is crucial for developing light-weight, reusable, high-speed vehicles. In this work, flow structures in a Mach 4 boundary layer are first studied over i) rigid flat plates to establish a baseline and ii) statically deformed geometries to investigate the flow response to surface deformation over longer time scales. Next, the flow response over a compliant steel panel under static and dynamic loading from an oscillating shock generator is investigated. Euler simulations are performed to design the geometry and location of the shock generator in the Caltech Mach 4 Ludwieg tube test section, predict the amplitude of the oscillation required to drive the pressure wave across the compliant surface, and to calculate the pressure rise on the compliant surface due to the dynamic load. Schlieren video, fast response pressure sensitive paint profiles, and laser displacement sensor measurements of the response of a 0.2 mm thick steel panel to loading from the shock generator are discussed and compared to similar measurements of the rigid case. The compliant panel center point deforms by nearly 4 panel thicknesses under these conditions and results in a flattened and elongated separation region at the interaction location and lower static pressure on the panel surface when compared to the rigid panel case.