NUMERICAL-SIMULATION OF MIXING ENHANCEMENT IN A HOT SUPERSONIC JET

Experimental observations show that the presence of small tabs on the edge of a hot, compressible jet exiting into a slower moving, colder a mbient flow can increase the rate of spreading of the jet. This sugges ts that the rate of mixing of the jet and the ambient fluid is also in creased. In order to elucidate the physical mechanism responsible for the increased spreading rate a set of calculations was carried out wit hin the framework of the compressible three dimensional Navier-Stokes equations. A series of grid refinements were made to assess the accura cy of the results. We first simulated the flow without the tabs, obtai ning reasonable agreement with experimental measurements of the veloci ty. We then simulated the flow, without tabs, over a range of values o f the convective Mach number in order to determine the dependence of t he mixing on this parameter. Simulations with modeled tabs were also c arried out. In these calculations the effect of the tabs on the flow w as modeled by pairs of counter-rotating vortices. The results of these calculations indeed show that the presence of the tabs increase the s preading rate of the jet. The basic physical mechanism responsible for the enhanced spreading rate is discussed and qualitative comparisons with flow visualizations are made. (C) 1997 American Institute of Phys ics.