Abstract In this research, the n-hexane jets discharged from a straight channel were studied numerically to reveal the development and characteristics of under-expanded flashing jets. Firstly, the development of flash boiling jets was investigated and compared to that of two-phase jets without phase transition. It was shown that the two-phase jets without phase transition can be under-expanded only if the flow is choked. In contrast, flash boiling jets can be under-expanded whether or not the choked conditions are verified. Secondly, the factors affecting the flashing jet behaviors were discussed. The relaxation time in phase transition, the expansion ratio, and the injection pressure have been identified as three key factors determining the jet characteristics. With high enough expansion ratio and low enough relaxation time, the expansion was so strong that the flow became transonic and shock structures similar to those of under-expanded gaseous jets appeared near the orifice exit. Finally, two types of choking have been identified for flash boiling jets, i.e., vaporization-induced choking and expansion-induced choking. The former one is mainly ascribed to the vapor formation in the orifice which reduces the local speed of sound, while the latter one is due to the expansion of under-expanded two-phase flow and the resultant flow acceleration.

中文翻译：

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了解欠膨胀闪沸射流的发展和特征

摘要 本研究通过对直通道喷射正己烷射流进行数值研究，揭示了欠膨胀闪蒸射流的发展和特征。首先，研究了闪蒸射流的发展，并与没有相变的两相射流进行了比较。结果表明，只有当流动被阻塞时，没有相变的两相射流才会膨胀不足。相比之下，无论是否验证了阻塞条件，闪蒸射流都可能膨胀不足。其次，讨论了影响闪蒸射流行为的因素。相变中的弛豫时间、膨胀比和注射压力已被确定为决定射流特性的三个关键因素。具有足够高的膨胀比和足够低的弛豫时间，膨胀如此强烈以至于流动变成了跨音速，并且在孔口出口附近出现了类似于膨胀不足的气体射流的激波结构。最后，已经确定了闪蒸射流的两种类型的阻塞，即汽化引起的阻塞和膨胀引起的阻塞。前者主要是由于孔口内的蒸汽形成降低了局部声速，而后者是由于未充分膨胀的两相流的膨胀和由此产生的流动加速。