Experimental and analytical investigation of injection behind a pylon in a compressible flow

Abstract

An experimental and analytical investigation of the mixing of a transverse jet behind a pylon in a supersonic freestream has been conducted. Shadowgraphs were used to view shock locations. Planar laser-induced iodine fluorescence was used to conduct injectant mole fraction measurements. A full three-dimensional Navier-Stokes calculation of this flow field was performed using the SPARK3D code. Despite limitations in the resolution of the experimental data due to the physical scale of the wind tunnel, good overall agreement between the experimental and the calculated results was obtained. For this geometry, a high degree of penetration and mixing was obtained. Introduction The development of viable SCRAMJET and hybrid rocket engines requires a thorough understanding of the supersonic mixing process. In building die knowledge base of the supersonic mixing problem, several different geometries and mixing methods have been proposed for study. Geometries investigated to date include circular cross-section injection at various angles of incidence to the flow, staged transverse injection-, transverse injection behind a rearwardfacing step*, swept (angled) ramp slot injection, and swirling jet pairs.* These flow fields have been studied using several different techniques including mass sampling, shadowgraph, schlieren, Rayleigh/Mie scattering and laser-induced fluorescence. Another injection technique that has potential is injection behind a pylon. Bogdanoff suggested this combination as an alternative to ramp injection. Copyright ° 1996 by Roy Hartfield Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. f Graduate Research Assistant * Assistant Professor, Member AIAA Possible advantages of pylon injection over ramp injection are lower drag, fuel delivery external to the pylon structure (injector outlet can be much larger than the equivalent ramp geometry could allow and, therefore, deliver more fuel), and enhanced mixing characteristics. This study concentrates on a simple version of the pylon injector geometry shown schematically in Fig. 1. This flow field is evaluated both experimentally and numerically.