Transition and Mixing in the Shear Layer Produced by Tangential Injection in Supersonic Flow

Abstract

The interaction between a viscous mixing layer induced by tangential injection, and an external supersonic flow field is considered experimentally and analytically. Both subsonic and supersonic injection are investigated. The experiments were performed at freestream Mach numbers of 2.85 and 4.19 using air as the injectant. The principal observations are in the form of spark schlieren photographs, interferograms, and wall pressure distributions. The experiments were arranged to cross Lin’s neutral stability boundary for parallel streams. Transition occurred in all cases, but an increase in stability was noted with either a decrease in the injectant Mach number or an increase in the Mach number of the external flow. Both of these results follow the trends predicted by the stability theory. For the supersonic injection cases, it was found that simple inviscid theory is sufficient to predict the overall interaction pattern between streams, when the ratio of initial boundary layer thickness to the injection slot height is small. However, when the injection is subsonic, the injectant initial conditions in terms of either pressure or Mach number at the slot exit are determined by the downstream viscous-inviscid interaction with the external supersonic flow. A simple one-dimensional theory is applied to this problem to enable prediction of the initial conditions.