Fluid Structure Interaction on a Compliant Panel subject to Shock Boundary Layer Interaction

Abstract

This work discusses results from an on-going effort towards the experimental investigation of the fluid-structure interaction on a compliant panel due to shock wave boundary layer interaction. Experiments were carried out to understand the unsteady aspects of fluid-structure interaction on a compliant panel subject to a 2D impinging shock generated by a 10̊ shock generator for a Mach 2 flow with Re=4.35x107/m, using two types of pressure field measurements: binary FIB to explain the mean pressure field and fast response pressure sensitive paint (PSP) to understand the unsteady flow features. These results were complemented by the surface deflection measurements underneath the panel mid-point and unsteady cavity pressure measurements to identify the flow, structural and acoustic cavity modes. Two shock impingement locations and three cavity pressures were tested. The compliant panel results were compared with the rigid plate, which served as a baseline model, to understand the differences between the interactions on the rigid and compliant surfaces. To provide a better understanding of the flow characteristics, a glimpse into the previous work which incorporated shadowgraph and surface oil flow measurements to highlight key qualitative differences between the rigid plate and compliant panel is given. Several interesting features were observed: 1) The interaction on the panel across cavity pressures was observed to be curved along the centerline compared to the nominally 2D straight line interaction observed over 70% span of the rigid plate. Also, the streamwise separation bubble length was observed to be largest along the centerline compared to other locations along the span, thereby indicating a spanwise variation. 2) No common trend was observed in the length of separation bubble for the two shock impingement locations. 3) An increase in the unsteadiness levels of the shock was observed for the interaction on the panel compared to the baseline case. 4) An increase in the centerline mean pressure compared to the baseline case was observed within the interaction for panel with cavity at ambient and upstream static pressure, followed by a decrease for the case with cavity at vacuum and subsequent increase in the magnitude of the mean pressure post reattachment across the three cavity pressures, compared to the baseline case was observed. This is indicative of the dominant effect of cavity pressure in defining the subsequent fate of the interaction. 5) Strong coupling was observed between the shock and the panel for the panel lower order structural modes for cases with cavity at ambient and upstream static pressures. However, for cavity at vacuum this coupling was observed with the panel higher order modes. The spectra from the single point deflection measurements and unsteady cavity pressure measurements strengthen these claims. 6) Higher order modes were observed to show a stronger coupling as the shock impingement location was moved downstream.