Effect of confinement on shock wave-boundary layer interactions

Abstract

Shock wave-boundary layer interactions (SWBLIs) are an inevitable feature of compressible flow and can have a large detrimental effect on the performance of aerodynamic applications. To address and design to accommodate them, requires detailed understanding of the underlying flow mechanisms. At present, our knowledge of these mechanisms is insufficient to accurately predict SWBLI behavior. This experimental study attempts to provide a better understanding of some of these mechanisms by focusing on the three- dimensionality inherent in oblique SWBLIs. The test configuration consists of an oblique shock wave in Mach 2 flow in a rectangular test section at flow deflection angles of 8° , 10° , and 12°. The key parameters of test section effective aspect ratio (AReff) and shock generator geometry are varied to assess their ability to amplify/attenuate the three-dimensionality of a nominally two-dimensional SWBLI. An innovative traversable shock generator with interchangeable wedge geometries allow the effects of AReff , expansion fan placement, and side-wall gap to be studied. The flow is investigated by employing Schlieren photography, surface flow visualization, static pressure measurements, Laser Doppler Anemometry and Particle Image Velocimetry. It is observed that with an increase in AReff, or a downstream movement of the expansion fan, or a decrease in side-wall gap, the SWBLI and shock-induced separation will grow. The growth of the separated region exhibits an increase in three-dimensionality and at high AReff the regular reflection is observed to evolve into a Mach reflection without an increase in incident shock strength. Models are proposed to explain the observed behavior as a function of separation growth and a reduction of the influence of free interaction theory.