圆球诱发斜爆轰波的数值研究

斜爆轰发动机是飞行器在高马赫数飞行条件下的一种新型发动机,具有结构简单、成本低和比冲高等优点.但是斜爆轰发动机的来流马赫数范围广,来流条件复杂,为实现斜爆轰波的迅速、可靠引发,采用钝头体来诱发.利用Euler方程和氢氧基元反应模型,对超声速氢气/空气混合气体中圆球诱导的斜爆轰流场进行了数值研究.不同于楔面诱发的斜爆轰波,球体首先会在驻点附近诱发正激波/爆轰波,然后在稀疏波作用下发展为斜激波/爆轰波.模拟结果显示,经过钝头体压缩的预混气体达到自燃温度后,会出现两种流场:当马赫数较低时,由于稀疏波的影响,燃烧熄灭,钝头体下游不会出现燃烧情况;而当马赫数较高时,燃烧阵面能传到下游.分析表明,当钝头体的尺度较小时,驻点附近的能量不足以诱发爆轰波,只会形成明显的燃烧带与激波非耦合结构;当钝头体的尺度较大时,流场中不会出现燃烧带与激波的非耦合现象,且这一特征与马赫数无关.通过调整球体直径,获得了激波和燃烧带部分耦合的燃烧流场结构,这一流场结构在楔面诱发的斜爆轰波中并不存在,说明稀疏波与爆轰波面的相互作用是决定圆球诱发斜爆轰波的关键.

NUMERICAL STUDY OF THE OBLIQUE DETONATION INITIATION INDUCED BY SPHERES

The oblique detonation wave engine is a new kind of engine which has a simple structure, low cost, and high specific impulse. In order to ensure the initiation, blunt body is used to induce the oblique detonation wave. The oblique detonation wave flow field induced by spheres in supersonic hydrogen/air mixture is numerically simulated, based on the Euler equations and a detailed hydrogen-oxygen chemical reaction model. Unlike the oblique detonation wave induced by a wedge, the reacting flow around a sphere is much more complex. First, a normal shock wave/detonation wave is formed, then oblique shock wave/detonation wave is developed in the presence of a rarefaction wave. The numerical simulation results show that after the gases being compressed by the blunt body and reaching the auto-ignition temperature, two kinds of flowfileds will appear. When Mach numbers are low, the combustion will be quenched and can not appear downstream of the blunt body due to the influence of the rarefaction wave. When Mach numbers are high, combustion can spread to the downstream region. When the scales of blunt body are small, energy around the stationary point is not enough to induce detonation initiation and an obvious decoupling of combustion and shock wave is formed. As the sphere becomes large enough, decoupling of combustion and shock wave will not appear in the flow and this feature is indpendent of the Mach number. By adjusting the spheric diameter, the flow structures with partial coupling of shock wave and combustion zone was obtained which does not exist in a wedgy-induced oblique detonation. The present investigations suggest that the interaction between rarefaction wave and detonation wavefront is the key issue for detonation initiation induced by a spheric body.