Abstract:
More and more people believe that opposing jetscan reduce the drag, which are obtained by the interaction of high speedcounter- flow jets and bow shock. It improves the performance of aircraft byshifting the flow field (shock wave structure and boundary layer)around the aircraft, changing the physical and aerodynamiccharacteristics ofthe aircraft. The flow field over the sphere and truncated cone, withcounter-flow jets, is investigated in the present paper. It takes intoaccount theeffect of the thermo-chemical non-equilibrium in the flow field. Two steadyflow modes of a truncated cone are obtained: short penetration mode (SPM) and long penetration mode (LPM). Details of bothmodes are studied. The transient phenomena during the transition from onemode to another are also investigated. The shock bifurcation phenomenon isstudied and the relation between flow field's stability and jettotal-pressure ratio is obtained. The numerical experiment reveals acritical state for theoscillatory fluid motion. The control parameter is the stagnation pressureratio between the on-coming stream and the counter-flow jet. At a lowinjection pressure, the jet is compressed, penetrates through the bowshock and forms a multi barrel structure. When the counter-flow jet isgenerated by a sufficient high stagnation pressure, it will assume a singlebarrel structure. When the jet pressure is in the critical range, a largeamplitude oscillation will occur and the drag attains its minimum value. Theuse of counter-flow jets in drag reduction is analyzed. The main factorsin the drag reduction's efficiency are also studied.
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