平面激波冲击柱形气体界面的实验研究

Experimental investigation on the interaction of planar shock wave with cylindrical gaseous inhomogeneity

采用高速纹影法实验研究了马赫数为1.2的平面激波冲击下柱形气体界面的演变发展过程.采用环约束的方法,利用肥皂膜技术形成了柱形界面.在单次实验中得到了平面激波与柱形界面作用的全过程,观测了波系发展以及气体界面的演化.结果表明,在激波冲击下SF6气柱下游界面会产生射流结构并最终发展成蘑菇形状;而氦气气柱受到激波冲击后会出现反相,上游界面发展出射流结构并穿透下游界面,最终界面发展成两个独立的涡结构.通过测量比较界面尺寸的变化,可以较清楚地了解界面变形的物理规律.最后将SF6气柱实验中获得的激波和气体界面的速度与一维气体动力学预测结果进行比较,吻合较好,从而验证了环约束方法在Richtmyer-Meshkov不稳定性实验研究中形成气体界面的可行性.

The interaction of a planar shock wave （Mach number of 1.2） with a gas cylinder （helium cylinder or SF6 cylinder） is experimentally studied using the high-speed schlieren photography. Because the soap film has less influence on the interface evolution than the solid diaphragm and the soap film cylinder can effectively suppress the gas exchange at the interface compared with the diaphragm-less cylinder, a circular wire-restriction method of using the soap film technique is introduced to generate the interface separating the experimental gas from the ambient gas. Illuminated by a DC source, the evolution of the gas cylinder accelerated by a shock wave is captured by the high-speed video camera in a single test run and the wave patterns are also observed. It is shown from the results that the SF6 cylinder is firstly compressed and accelerated by the shock, and then a jet is formed at the downstream interface due to the transmitted shock focusing. Subsequently, induced by the vorticity, the cylinder is developed into a mushroom shape and finally the turbulent mixing occurs. After the impact of the shock wave, the helium cylinder is firstly accelerated and the reversal phase occurs at the upstream interface. Afterwards, a jet is generated from the upstream interface and gradually tears through the downstream interface. Eventually, the interface is developed into two independent vortexes. Compared with the previous studies, the results in this work behave more symmetry and fewer disturbances are generated in the flow field due to the absence of the holder. Moreover, the variation of the interface scales with time is measured from which the changes of the interface can be well interpreted. At last, the shock and interface velocities in SF6 case obtained in the experiment are found to have a satisfactory agreement with the theoretical prediction from one-dimensional gas dynamics, which verifies the interface formation method to some extent.