Abstract
A three-dimensional numerical simulation of a supersonic free-stream at Mach 2.5 over a spherical body with a sonic opposing jet from its stagnation point is carried out by solving the three-dimensional Navier–Stokes equations coupled with the standard k–ɛ turbulence model. It is aimed to investigate the effects of the jet on the drag reduction on the body and the flow field around the body. The influences of the jet pressure, the nozzle size of the jet, and the angle of attack are systematically studied for the purpose. An unsteady oscillatory motion mode and a nearly steady motion mode are identified depending upon the jet total pressure. There exists a critical jet pressure where the flow mode transition from one to the other happens suddenly and this critical pressure value varies approximately linearly with the jet nozzle exit size inversely. For the zero angle of attack, the results show that there exists a maximum overall drag reduction as the jet pressure changes for each jet nozzle size and the maximum overall drag reduction always happens at the unsteady oscillatory motion mode. The main shock in front of the body is pushed backward by the jet and the displacement of the shock decreases with the increase of the angle of attack, and the drag reduction efficiency also decreases with the angle. Regarding to the mode transition, it is found that the drag rises suddenly when the transition happens for the angle of attack smaller than or equal to 5° but it does not result in the rise for the angle larger than 5°. The results show that the maximum overall drag reduction can be reached as high as 32.6% for the cases studied. The present results provide useful information for drag reduction applications using an opposing jet.
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