A Study of Flow Unsteadiness Due to an Impinging Oblique Shock-Wave Boundary Layer Interaction

Abstract

This campaign was undertaken with a primary objective of understanding the characteristics of wall static pressure in a 3D oblique impinging shock-wave boundary layer interaction (IOSWBLI) generated by a wedge in a rectangular channel. This is important from the perspective of understanding the factors that lead to unstart and unsteady loading due to IOSWBLIs in engine inlets of aircraft which operate in high Mach number regime. In this regard, an IOSWBLI was generated in the UA Supersonic Wind Tunnel test section, at a free stream Mach number of 2.9, using an oblique shock-wave generated by a 12° isosceles wedge installed on the base of the test section. Oil flow visualization was conducted on the wall opposite the wedge (top-wall) and one of the side walls. Unsteady pressure measurements were acquired on the same top and side walls utilizing pressure transducers. The results revealed a decreasing value of peak pressure rise past the shock-wave on moving from tunnel centerline towards the sidewall which indicates the presence of a 3D IOSWBLI, and energy content concentrated mostly in the frequency range of 200-1000 Hz in the interaction region. Concurrently, a steady-state 3D and unsteady 2D IOSWBLI (at tunnel centerline) were simulated in the software ANSYS (FLUENT), with the same experimental boundary conditions and test section geometry. The results from the 3D and 2D simulations captured pressure rise trends and frequency content of the flow in the interaction region that aligned with the experimental results. Additionally, 3D simulation also predicted a vortical flow near the walls that is opposite in value, maintaining symmetry about the tunnel centerline and the plane of impinging shock-wave. The secondary objective was to capture the pressure and strain effects an IOSWBLI impresses on a thin structure. This is a fluid structure interaction that can be detrimental to aircraft panels. In this experiment, a dual-layer luminescent coating was used to measure the pressure and strain on a thin, circular clamped plate subjected to an IOSWBLI in the same facility, using a 12° right angled wedge. The two-coating technique uses a fast-response pressure sensitive paint (PSP) applied over a photo-elastic Coating (PEC) adhered to the surface of the plate. The results using a low-speed micropolarizer camera with four polarization orientations show that the technique is sensitive to pressure and strain, measuring a pressure field topography that overlaps with the oil flow visualization conducted separately and a strain field where the maximum shear strain is along the clamped edge of the plate.