Belan Marco, De Ponte Sergio, Tordella Daniela
Dipartimento di Ingegneria Aeronautica e Spaziale, 20156 Milano, Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Aug;82(2 Pt 2):026303. doi: 10.1103/PhysRevE.82.026303. Epub 2010 Aug 10.
An experimental research concerning highly underexpanded jets made of different gases from the surrounding ambient is here described. By selecting different species of gases, it was possible to vary the jet-to-ambient density ratio in the 0.04-12 range and observe its effect on the jet morphology. By adjusting the stagnation and ambient pressures, it has been possible to select the Mach number of the jets, independently from the density ratio. Each jet is therefore characterized by its maximum Mach number, ranging from 10 to 50. The Reynolds number range of the nozzle is 10(3)-5×10(4). The spatial evolution of the jets was observed over a much larger scale than the nozzle diameter. The gas densities were evaluated from the light emission induced by an electron beam and the gas concentrations were obtained by analyzing the color of the emitted light. The results have shown that the morphology of the jets depends to a greater extent on the density ratio. Jets that are lighter than the ambient exhibit a more intense jet-ambient mixing than jets that are heavier than the ambient, while the effects of changing the jet Mach number do not seem to be too large in the explored range. These results can be expressed by means of two simple scaling laws relevant to the near field (pre-Mach-disk) and the mid-long term field (post-Mach-disk), respectively.
本文描述了一项关于由周围环境中不同气体产生的高度欠膨胀射流的实验研究。通过选择不同种类的气体，可以在0.04至12的范围内改变射流与环境的密度比，并观察其对射流形态的影响。通过调节滞止压力和环境压力，可以独立于密度比来选择射流的马赫数。因此，每个射流的特征在于其最大马赫数，范围从10到50。喷嘴的雷诺数范围为10(3)-5×10(4)。观察到射流的空间演化尺度比喷嘴直径大得多。通过电子束诱导的发光来评估气体密度，并通过分析发射光的颜色来获得气体浓度。结果表明，射流的形态在很大程度上取决于密度比。比环境轻的射流比比环境重的射流表现出更强的射流与环境的混合，而在探索的范围内改变射流马赫数的影响似乎不太大。这些结果可以分别通过与近场（马赫盘之前）和中长期场（马赫盘之后）相关的两个简单比例定律来表示。
