TANGENTIAL INJECTION FROM OVERLAID SLOTS INTO A SUPERSONIC STREAM

The results of an experimental study of tangential supersonic slot inj ection into a supersonic airstream with tangential subsonic injection through an additional slot above the main slot is presented, Such a no w is of interest for at least two propulsion-related applications. Fir st, one can simulate a near-separation boundary-layer profile by subso nic injection through the upper slot, which is then to be re-energized by supersonic injection through the lower slot, Second, this now is a lso of interest for application to fuel/oxidizer/pilot injection from multiple overlaid slots, The experiments were performed in an intermit tent, vacuum wind tunnel at a freestream Mach number of 2.85, The supe rsonic 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 th e form of spark schlieren photographs, interferograms, and wall-static pressure measurements, Density profiles at several axial locations de termined from the interferograms are presented, as well as streamwise and spanwise static pressure distributions. The major conclusions draw n from the tandem injection results, are first, that a near-separation boundary-layer profile can be simulated in this way, Next, tandemly i njected subsonic and supersonic how can be divided into separate compo nents 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 height s, Therefore, adverse-pressure-gradient-inducing devices should be pos itioned at least six slot heights downstream of the supersonic injecti on station if the effects of supersonic injection into a near-separati on boundary layer for the purpose of re-energizing it are to be studie d.