A note on the generation of a compressible vortex rings using helium as driver gas
A note on the generation of a compressible vortex rings using helium as driver gas
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DOI：
10.1177/0954410012465042
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发表时间：
2013-10
期刊：
影响因子：
--
通讯作者：
R. Mariani;M. K. Quinn;K. Kontis
中科院分区：
文献类型：
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作者：
R. Mariani;M. K. Quinn;K. Kontis
本文对氦气驱动的可压缩涡环的产生和传播进行了实验研究，目的是评估多气体操作对实际应用的影响。与基于环境空气的恒定气体系统相比，这种系统的优点是有效地增加马赫数，同时保持压力比恒定。设定了三个压力比，分别为1.44、8和12，对应的实验马赫数约为1.50、1.81和2.05。随着来流马赫数的增加，涡环和尾喷流结构发生了变化，速度和涡量场均增大。结果表明，在实验马赫数约为1.50时，从规则反射激波单元系统过渡到具有中心马赫盘的马赫反射系统，中心马赫盘的尺寸随着入射马赫数的进一步增加而增大。马赫盘的存在导致在主尾喷流内部形成亚音速喷流。它的速度被测量为550 m/s的数量级，氦的声速为1005 m/s。结果还表明，亚音速和主尾喷流之间形成的剪切层具有相反的涡量，亚音速喷流的涡量约为一半。在主涡之前产生了反向旋转的二次涡环并围绕主涡旋转，涡量场分析表明，这些二次涡的大小约为主涡量的一半，并证实它们具有相反的旋转方向。
An experimental study has been conducted on the generation and propagation of compressible vortex rings using helium as a driver gas, with the aim of evaluating the effects of multi-gas operations for real-life applications. The advantage of such system, when compared to a constant gas system based on ambient air, is to effectively increase the Mach number while keeping the pressure ratio constant. Three pressure ratios of ∼4, 8 and 12 were set, corresponding to experimental Mach numbers of approximately 1.50, 1.81 and 2.05. The increase in incident Mach number resulted in the variation of the vortex ring and trailing jet structure, and an increase in both the velocity magnitude and vorticity field. Results showed a transition from the regular-reflection shock-cell system at the experimental Mach number approximately 1.50 to the presence of a Mach reflection with a central Mach disc, which grew in size with further increase in incident Mach number. The presence of the Mach disc resulted in the formation of a subsonic jet, internal to the main trailing jet. Its velocity was measured to be in the order of magnitude of 550 m/s, with the speed of sound of helium at 1005 m/s. Results also demonstrated that shear layers formed between the subsonic and main trailing jet have opposing vorticity, with that of the subsonic jet being approximately half in magnitude. Secondary counter-rotating vortex rings were generated ahead of the main vortex and orbited around it. The analysis of the vorticity field has shown that these secondary vortices have a magnitude approximately half of that of the vorticity of the main vortex, and has confirmed that they have an opposite direction of rotation.