逆向喷流流场模态分析及减阻特性研究

PENETRATION MODE AND DRAG REDUCTION RESEARCH IN HYPERSONIC FLOWS USING A COUNTER-FLOW JET

逆向喷流减阻的基本原理是利用逆向高速喷流与飞行器绕流的相互作用,使飞行器周围的流场结构发生变化,致使飞行器的气动特性发生改变,从而改善飞行器的气动性能．利用数值模拟方法对轴对称球头、截锥的逆向喷流流场开展了研究,考虑了高温非平衡化学反应对流场的影响．模拟了球头和截锥在不同总压比时流场不同的模态:长穿透流模态(LPM)和短穿透流模态(SPM),得到了不同模态下钝体表面压力、气动力系数和不同模态之间转换的瞬态效应．简单分析了喷流在减阻方面的应用,给出了几个喷口参数与减阻效率之间的关系,提出了喷流减阻工程应用时应考虑的主要因素．

More and more people believe that opposing jets can reduce the drag, which are obtained by the interaction of high speed counter- flow jets and bow shock. It improves the performance of aircraft by shifting the flow field （shock wave structure and boundary layer） around the aircraft, changing the physical and aerodynamic characteristics of the aircraft. The flow field over the sphere and truncated cone, with counter-flow jets, is＇investigated in the present paper. It takes into account the effect of the thermo-chemical non-equilibrium in the flow field. Two steady flow modes of a truncated cone are obtained： short penetration mode （SPM） and long penetration mode （LPM）. Details of both modes are studied. The transient phenomena during the transition from one mode to another are also investigated. The shock bifurcation phenomenon is studied and the relation between flow field＇s stability and jet total-pressure ratio is obtained. The numerical experiment reveals a critical state for the oscillatory fluid motion. The control parameter is the stagnation pressure ratio between the on-coming stream and the counter-flow jet. At a low injection pressure, the jet is compressed, penetrates through the bow shock and forms a multi barrel structure. When the counter-flow jet is generated by a sufficient high stagnation pressure, it will assume a single barrel structure. When the jet pressure is in the critical range, a large amplitude oscillation will occur and the drag attains its minimum value. The use of counter-flow jets in drag reduction is analyzed. The main factors in the drag reduction＇s efficiency are also studied.