气相爆震波马赫反射转变机理的实验研究

Experimental Study of Transition Mechanism of Mach Reflection of Detonation Wave

关键词:  气相爆震  马赫反射  胞格结构  过驱

Key words:  Gaseous detonation  Mach reflection  Cellular structure  Overdriven

摘要:

在矩形爆震管道中，选用具有规则胞格结构的高浓度氩气稀释稳态气体C2H2-2.5O₂-8.17Ar及不规则胞格结构的非稳态气体C2H2-5N2O，利用纹影和烟膜实验对CJ爆震状态下的爆震波发生马赫反射的转变机理进行了研究。在楔角为30°，5kPa初始条件下，C2H2-2.5O₂-8.17Ar马赫反射转变时马赫杆临界高度约为1.25cm，过驱胞格结构出现的最小距离略小于胞格长度的1/3；C2H2-5N2O马赫反射转变时马赫杆临界高度约为1.5cm，由于其胞格结构不规则，故难以衡量过驱胞格结构出现的位置。实验结果表明:爆震波马赫反射三波点运动轨迹特征为在初始阶段遵循无反应冲击波理论，随后马赫反射发生转变使得运动轨迹逐渐平行于反应冲击波理论，从而验证了爆震波开始形成前导激波马赫反射，由于CJ区域内三波点的介入引起扰动，最终在马赫反射区形成过驱爆震的过程。

Abstract:

Using Schlieren photography and smoked foils，transition mechanism of Mach reflection of detonation wave under CJ state was studied experimentally in a rectangular channel. Stable mixture C2H2-2.5O₂-8.17Ar highly diluted by argon with fairly regular cellular pattern and unstable mixture C2H2-5N2O with irregular cellular pattern were used for experiments. At wedge angle 30°，5kPa initial conditions，the critical height of Mach stem was about 1.25cm when transition of Mach reflection happened in C2H2-2.5O₂-8.17Ar and the minimum distance for appearing overdriven cell structure was slightly less than 1/3 of cell length. While for C2H2-5N2O，the critical height of Mach stem was about 1.5cm and it was difficult to measure the distance due to its irregular cellular structure. The experimental results demonstrate that trajectory of Mach reflection in detonation waves follows triple point trajectory of non-reactive shock theory at beginning of wedge，and then falls on a line parallel to triple point trajectory of reactive shock theory when transition of Mach reflection happens，which verifies that Mach reflection of leading shock is formed at beginning of wedge in detonation waves，and then transforms into overdriven detonation in Mach reflection region owing to perturbations yielded by triple points in CJ region.