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 ambient ow can increase the rate of spreading of the jet. This suggests that the rate of mixing of the jet and the ambient uid is also increased. In order to elucidate the physical mechanism responsible for the increased spreading rate a set of calculations were carried out within the framework of the compressible three dimensional Navier-Stokes equations. A series of grid re nements were made to assess the accuracy of the results. We rst simulated the ow without the tabs, obtaining reasonable agreement with experimental measurements of the velocity. We then simulated the ow, without tabs, over a range of values of the convective Mach number in order to determine the dependence of the mixing on this parameter. Simulations with modeled tabs were also carried out. In these calculations the e ect of the tabs on the ow was modeled by pairs of counter rotating vortices. The results of these calculations indeed show that the presence of the tabs increase the spreading rate of the jet. The basic physical mechanism responsible for the enhanced spreading rate is discussed and qualitative comparisons with ow visualizations are made. The rst, third and fourth authors were supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-19480 while in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research, Hampton, VA 23681-0001.