DECAY OF SUPERSONIC RECTANGULAR JET ISSUING FROM A NOZZLE WITH DIAGONAL EXPANSION RAMPS

This paper addresses the effect of expansion ramps on the decay characteristics of a controlled supersonic rectangular jet. A Mach 1.8 rectangular jet issuing from a converging-diverging nozzle of aspect ratio 2 and Reynolds number 1.861.10(5) is considered as the base model for the study. Two separate nozzle models with expansion ramps placed at the diagonal ends on major and on the minor internal surface are considered for the present study. The diagonal placements of ramps induce additional vortices near the nozzle exit apart from the corner vortices emanating from the rectangular corners. Experimental and computational investigations at different expansion levels are carried to prove the enhanced mixing rate due to the induced vortex. The ramps on the minor side caused maximum supersonic core length reduction of 44% at an inlet total pressure of 4 bar and a minimum of 27% at an inlet total pressure of 8 bar. The maximum and minimum core length reductions caused by the ramps placed on the major side are 22% and 11% at inlet total pressures 6 and 8 bar respectively. Both experimental and numerical studies show that shock waves are rendered weak by the minor side placement of ramps at all expansion levels.