Research on the interactions between compressible vortex rings and the properties of generated shocklets

本文研究了亚音速非定常流运动中出现的可压缩性效应。实验中使用的基本流是从激波管开口端发出的激波后面的流动。该流在激波管内连续排出的非定常流的头部有一个旋涡环。首先，利用光学阴影法研究了基流的动态运动。接下来，用同样的方法研究了更复杂的流动中出现的现象，这些现象是由基本流与其他变量的相互作用产生的。下面将简要讨论以下结果。头涡环的核心包括一个涡度强烈集中的内核及其周围的涡片。在层流向湍流涡旋环过渡的过程中，这两个部分独立地变成了湍流样。在头涡环内产生后向激波后，在头涡环前出现一个很薄的涡环。薄涡环将其位置反转到头涡环的后部，将其位置反转到头涡环的后部。头涡环后的非定常流受到弱激波的激励，形成小涡环。这些小漩涡环随后相互作用，然后这些小漩涡环与相邻的漩涡环合并。超声速区在更复杂的流动中发展，并产生激波。压力急剧增加的焦点是激波和小涡环相互作用的结果。这些结果表明，头涡环后的非定常流场对当前流场中出现的可压缩性效应有重要的作用。

The present study is concerned with the compressibility effects appearing in the motion of an unsteady flow that is initially subsonic. A fundamental flow, used in experiments, is the flow following behind the shock wave emitted from the open end of a shock-tube. This flow has a vortex ring at the head of the unsteady flow discharged continuously out of a shock-tube.First, the dynamic motions of a fundamental flow were studied by means of an optical shadowgraph method. Next, the phenomena appearing in more complex flows, produced by the interactions of a fundamental flow with other variables, were studied by the same method. The following results are discussed briefly below.The core of a head vortex ring includes a inner core with strongly concentrated vorticity and a vortex sheet surrounding it. These two sections become turbulent-like independently, during the process of the transition from a lamminar to a turbulent vortex ring. Afrer rearward-facing shocklets are generated within the head vortex ring, a very thin vortex ring appears in front of the head vortex ring. The thin vortex ring reverses its position to the rear of the head vortex ring reverses its position to the rear of the head vortex ring. The unsteady flow behind the head vortex ring, is excited by a weak shock wave, which results in the production of small vortex rings. These small vortex rings subsequently interact with each other, and then these small vortex rings merge with the adjacent ones.Supersonic zones develop within more complex flows, and shocklets are generated. The point of focus, at which the pressure increases dramatically, is produced as a result of these interactions between the shocklets and the small vortex ring.These results indicate that the unsteady flow following behind a head vortex ring makes significant works for the compressibility effects appearing in the present flow fields.