A Qualitative Comparison of the Effect of Exit Ramps and Coaxial Subsonic Jet on Primary Supersonic Jet

Abstract

This work is to study and compare the behavior of supersonic jet with induced vortices and co-flow. Characteristics of a supersonic jet like potential core length, total pressure decay and shock cell formations are concentrated. In this study, the influence of subsonic coaxial flow on the rectangular supersonic jet (primary) with vortices induced by expansion ramps has been analyzed in detail. Rectangular exit C-D nozzles with different ramp angles are used. Angles of expansion ramps are varied, and exit area, area ratio and pressure ratio for exit Mach Number of 1.8 are maintained the same for all the nozzles. An annular Co-flow duct issuing subsonic flow is used with the primary nozzle. These two different coaxial streams at different Mach numbers are allowed to mix. Subsonic co-flow with primary supersonic jet can affect the mixing characteristics of the primary supersonic jet. Along the centerline axis of the primary jet, total pressure decay was calculated by using 16-channel intelligent pressure scanning systems connected with pitot tube fitted in the three directional traverse mechanism. A twin mirror Schlieren system had been employed to capture the shock patterns at the exit of nozzles. Comparing the pressure decay results, the total pressure decay of rectangular jet with induced vortices and co-flow is 28% higher than the simple rectangular jet. Length of shock cell formation is also decreased for rectangular jets with induced vortices than others. And also it is noted that the jet spread rate and distance are appreciably increased with the increment in expansion angle of ramps. From the above study, it is concluded that the jet field mixing properties are strongly influenced by the exit face (primary nozzle) expansion ramps and co-flow.