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超音速尾流作用下通气空泡稳定性及闭合位置数值研究

NUMERICAL STUDY ON THE STABILITY AND CLOSURE POSITION OF VENTAILATED CAVITY WITH A SUPERSONIC TAIL JET

  • 摘要: 以喷气推进为动力的水下超空泡航行体, 通气空泡的稳定性和空泡形态控制问题是关键所在. 本文利用VOF耦合水平集界面追踪方法, 考虑气体的可压缩性, 通过改变射流强度和模型长度, 开展了一系列通气空泡和超音速尾射流相互作用的数值仿真, 重点分析了通气空泡的稳定性和闭合位置. 数值结果表明: (1)在超音速尾射流作用下, 通气空泡的界面会经历膨胀、颈缩、断裂回缩过程, 然后开始周期性震荡泄气. 通气空泡的形态长度相较于无射流条件下大大减小; (2)气液界面两侧强剪切有可能诱导空泡失稳溃灭, 而这种空泡失稳机制主要取决于两个无量纲参数 \overline J (射流推力和空化器阻力之比)和 \overline L (模型长度和空化器直径之比), \overline J 越大, \overline L 越小, 空泡越容易失稳. 在此基础上, 进一步总结了算例中出现稳定和失稳两种状态的临界曲线; (3)空泡越稳定, 喷管出口的压力波动的幅度和频率就越低, 此时通气空泡能为火箭发动机提供稳定的工作; (4)对于空泡失稳的工况, 空泡闭合在喷管出口; 而空泡稳定的工况, 喷管出口到闭合位置的长度只与 \overline J 有关, 与模型长度无关.

     

    Abstract: For underwater supercavitation vehicles powered by jet propulsion, the stability and morphological control for ventilated cavity are the key issues. In this paper, we use the VOF coupled level set interface tracking method, the compressibility of the gas is considered. By changing jet strength and model length, a series of numerical simulations is studied on the interaction between ventailated cavity and supersonic tail jets, and focused on the stability and closed position of the cavity. The numerical results show that: (1) under the action of the supersonic tail jet, the interface of the ventilated cavity will experience expansion, necking, fracture and retraction, and then begin to periodically oscillate and deflate. The morphological length of the ventilated cavity is greatly reduced compared with that under the condition of no jet. (2) Strong shear on both sides of the gas-liquid interface may induce cavity instability and collapse, and this cavity instability mechanism mainly depends on two dimensionless parameters \overline J (the ratio of jet thrust and cavitator resistance) and \overline L (the ratio of the model length to the diameter of the cavitator). The larger \overline J and the smaller \overline L , the more easily the cavity is destabilized. On this basis, the critical curves for the two states of stability and instability in the calculation examples are further summarized. (3) The more stable the cavity, the lower the amplitude and frequency of the pressure fluctuation at the nozzle outlet. At this time, the ventilated cavity could provide stable ambience for the rocket engine. (4) For the condition of instability cavity, the cavity is closed at the nozzle outlet; while for the stable cavity, the length from the nozzle outlet to the closed position is only related to the parameter \overline J , but not to the model length.

     

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