两相射流与空化问题对采用喷气推进的水下高速运载器而言不可避免.本文通过水洞实验,探究了回转体在水流场中由亚声速及超声速气体射流诱导形成尾空泡的形态特征,发现了四种不同类型的诱导尾空泡,并探讨了相应的形成机理和控制条件.通过高速图像采集及数字处理技术,得到了不同弗劳德数和通气流量系数下诱导尾空泡的瞬时及时间平均形态.通过气体射流数值解及射流耦合空泡闭合理论模型与实验图像的对比分析,得到如下结论:根据形态特征,将观察到的射流诱导尾空泡划分为泡沫状、完整、部分破碎和脉动泡沫状四类,其中诱导产生的部分破碎尾空泡在形态上与超空泡存在明显差异,脉动泡沫状则为诱导空泡所特有;气体射流受到空泡阻挡发生回射后对应的实际通气流量系数是控制空泡形态的关键;诱导空泡类型转变可以通过Paryshev提出的射流空泡耦合模型预测,但必须在考虑射流空间结构和流动损失的前提下;进行上述修正后,诱导尾空泡形态变化规律与理论模型估算得到的实际流量系数相符合.%Multiphase jets and cavitation problems are inevitable for high-speed underwater vehicles propelled by jet engines. Unlike being injected into stagnant water, the gaseous jet behind a underwater vehicle is usually conjugated with a tail cavity. The pulsation and collapse of such cavities can seriously affect the vehicle performance. In this study, the shape character, forming mechanism and control conditions for the supersonic gaseous jet induced tail cavity at the wake of a revolution body are experimentally investigated in a water tunnel. The induced cavity is ventilated only by a convergent-divergent nozzle with a designed Mach number of 2.45. The form of the cavity is recorded through two high-speed cameras both horizontally and vertically under different Froude numbers and ventilation rates. The time averaged form is thus obtained through digital image processing to eliminate the transient characteristics of the cavity. The experiment is conducted with the Froude number ranging from 3.2 to 16.2, and the ventilation rate 0 to 0.5. Due to the high density and velocity ratio between water and gas, the structure of such flow is usually very complicated. Many novel phenomena of the jet-cavity interaction are observed. With increasing stagnation pressure of the central jet, the induced cavities evolves form foamy, intact, partially break, to pulsating foamy closure type. The foamy and intact tail cavities share the same profile and characteristics that of a supercavity. And the pulsating foamy closure type was never observed before in a traditional supercavitating flow. The outline of the pulsating foamy cavity is the same as the foamy cavity's, indicating that they have the similar forming mechanism. A comparison with the jet-cavity interaction model is made and the following conclusions are obtained: the real ventilation rate, which corresponds to the re-entrant jet gas blocked by the cavity boundary, is the key factor in controlling the cavity form. When the gaseous jet is completely blocked by the water-gas interface, an intact or foamy cavity will be formed. A partially break cavity appears only when some fraction of the jet is blocked and this is when some of the strongest interactions between jet and cavity occurs. When little gas was blocked by the interface, a pulsating foamy cavity forms. With the structure of gaseous jet considered, the transition of the induced cavity closure between different types is in favour of the prediction from Paryshev's model of cavity closure to a central jet. The variation of the cavity form, thus the interaction strength between jet and cavity, coincides with the real ventilation rate estimated through the theoretical model.
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