Tangential Injection from Overlaid Slots into a Supersonic Stream

Abstract

The results of an experimental study of tangential supersonic slot injection into a supersonic airstream with tangential subsonic injection through an additional slot above the main slot is presented. Such a  ow is of interest for at least two propulsion-related applications. First, one can simulate a near-separation boundary-layer proŽ le by subsonic injection through the upper slot, which is then to be re-energized by supersonic injection through the lower slot. Second, this  ow is also of interest for application to fuel/ oxidizer/pilot injection from multiple overlaid slots. The experiments were performed in an intermittent, vacuum wind tunnel at a freestream Mach number of 2.85. The supersonic injectant had a Mach number of 2.00, and the subsonic injection was at Mach numbers of 0.26 and 0.72. The results are presented in the form of spark schlieren photographs, interferograms, and wall-static pressure measurements. Density proŽ les at several axial locations determined from the interferograms are presented, as well as streamwise and spanwise static pressure distributions. The major conclusions drawn from the tandem injection results, are Ž rst, that a near-separation boundary-layer proŽ le can be simulated in this way. Next, tandemly injected subsonic and supersonic  ow can be divided into separate components that closely resemble the respective individual injections into an undisturbed freestream. Also, the effects of the subsonic injection were completely mixed out at a downstream location of six slot heights. Therefore, adverse-pressuregradient-inducing devices should be positioned at least six slot heights downstream of the supersonic injection station if the effects of supersonic injection into a near-separation boundary layer for the purpose of re-energizing it are to be studied.