Mixing Characteristics of Underexpanded Elliptic Sonic Jets from Orifice and Nozzle

摘要

The mixing characteristics of elliptical sonic jets issuing from an orifice and a convergent nozzle with an identical elliptical exit of aspect ratio of two were studied experimentally in the presence of favorable pressure gradients corresponding to nozzle pressure ratios of two to five, in steps of one. To quantify the aerodynamic mixing of the free jets with the fluid entrained from the surrounding environment, the jet centerline pitot pressure distribution and radial pitot pressure profiles along the major and minor axes directions of the jet were measured. The centerline pitot pressure variation of the orifice and nozzle jets shows that the decay of the jet from the nozzle is faster than the jet from the orifice at nozzle pressure ratios more than two. But at a nozzle pressure ratio of two, the decay of both the jets are close to each other. The pressure profiles demonstrate that the axis-switching location shifts upstream with an increase of nozzle pressure ratio for both the jets, implying that the near-field mixing is enhanced by the increase in the favorable pressure gradient The waves prevailing in the jet field were visualized with the shadowgraph technique.