Generation of Air/SF_6 Interface with Minimum Surface Feature by Soap Film Technique

摘要

A simple method of generating gas cylinders is proposed by using the soap film technique. The formed interface is free of supporting mesh and the initial shape can be accurately described in mathematics. As a result, the schlieren images of the shocked 2D cylinder have less disturbing waves and the evolving interfaces are more symmetric comparing with the results in literature. Because of the sharp interface, the main vortex and secondary instabilities are more pronounced in our 2D results. Therefore, the quality of the experiments of the shock-cylinder interaction is improved by using the well-controlled initial condition and can provide a good benchmark for numerical codes and analytical models. Special attention is then given to the 3D effects caused by the minimum surface feature on the interface evolution. It is found that there are two downstream interfaces in the 3D SF_6 cylinder case. The development of the shocked 3D cylinder is slower than that of the 2D counterpart, which can be 'adverse' pressure gradients and baroclinic vorticities related to the 3D initial shape. Due to the 3D characteristic, the evolving interface at each y-plane behaves differently and may interact with each other, which cannot be resolved by the integral visualizing method used in the present work. The effects of the liquid droplets produced by the soap film breakup, cylinder diameter, and Mach number on the RM instability also need further investigation. This research was carried out with the support of the National Natural Science Foundation of China, Grant No. 10972214 and by the Knowledge Innovation Program of the Chinese Academy of Sciences, Grant No. CX2090050020.