超音速来流中爆轰波衍射和二次起爆过程研究

Numerical investigation on detonation diffraction and re-initiation processes in a supersonic inflow

预爆管技术被广泛地应用在爆轰波发动机的起爆过程中,但是在超音速来流中基于预爆管技术起始爆轰波的研究并未被广泛地开展。基于此,本文中数值研究了横向超音速来流对半自由空间内爆轰波的衍射和自发二次起爆、及管道内的衍射和壁面反射二次起爆两种现象的影响。数值模拟的控制方程为二维欧拉方程,空间上使用五阶WENO格式进行数值离散,采用带有诱导步的两步链分支化学反应模型。所模拟的爆轰波具有规则的胞格结构,对应于用惰性气体高度稀释过的可爆混合物中形成的爆轰波。结果表明:在半自由空间内,在本文所模拟的几何尺寸下,爆轰波并未成功发生二次起爆现象,但是爆轰波的自持传播距离随着横向超音速来流强度的增强而增加。在核心的三角形流动区域外,波面诱导产生了更多的横波结构;在管道内,横向的超音速来流在逆流侧对出口气流产生了压缩作用,能有效提高波面压力,因此反射后的激波压力也比较高。在同样的几何尺寸下,爆轰波在静止和超音速(Ma=2.0)气流中分别出现了二次起爆失败和成功两种现象,这是由于在超音速来流中化学反应面的褶皱诱导产生了横波结构,横波与管壁以及其他横波之间的碰撞提高了前导激波的强度,并最终促进了爆轰波在超声速流主管道内的成功起始。

It is an effective way to initiate detonation with the aid of a pre-detonator in the detonation engines, and the initiation process by the pre-detonator has been widely investigated in static and subsonic flows. However, how to initiate a detonation wave with a pre-detonator in the supersonic flow was little dealt with in the literature and still needs to be intensively investigated. The diffraction and re-initiation processes during a planar detonation wave propagates into the supersonic inflow were numerically investigated in this paper. The detonation initiation processes both in a semi-infinite space and a confined channel were studied.The governing equations are two-dimensional in-viscid Euler equations. The high-accuracy WENO scheme was utilized in the simulations. The chemical reaction model is a two-step chain branching kinetic model with induction and reaction steps. The cellular structure of detonation wave is regular which is corresponding to the detonation wave formed in the detonable mixture highly diluted with inert gas. It was shown that the maximum distance of detonation propagation increased as the Mach number of supersonic inflow in the semi-infinite space. More transverse waves were generated outside the kernel zone. However, the reinitiation of detonation was failed in the geometry utilized in this work. In the confined channel, the reinitiation process was greatly influenced by the reflected waves. The emerged flow was compressed at the upstream side when the supersonic inflow was added and the pressure of the shock wave was increased accordingly. Compared with the failure of detonation re-initiation in the static flow, the re-initiation of detonation was successfully triggered in the supersonic inflow with Ma=2.0, despite the two cases used the same geometry. It was because that the wrinkles occurred on the reaction front and then resulted in the generation of transverse waves in the supersonic inflow. Because of the collisions between transverse waves,or between the transverse wave and the wall, the pressure decay of the leading shock wave was suppressed.Consequently, a successful re-initiation of detonation was occurred.