水下自激脉冲射流装置流场的数值模拟及试验研究

利用自行研制的淹没射流试验平台进行水下自激脉冲射流试验,得到水下自激脉冲射流驻点压力的径向和轴向分布,通过建立相应的物理模型和数学模型,对水下自激脉冲射流内外流场进行了数值模拟,得到装置内、外流场的压力和速度分布,并对计算结果进行试验验证.结果表明:自激脉冲射流在非淹没条件下,有明显的低频脉冲发生,而在淹没条件下,部分射流能量消耗在淹没水流中,以致在腔室内难以形成空化,没有产生明显的脉冲,且驻点压力大幅度减小;不同水深的径向压力分布曲线基本是相同的,近似服从高斯正态分布;轴向驻点压力均随靶距的增大而减小,其衰减特性与连续射流及非淹没情况相似,只是其在有围压情况下衰减速度更快;水下自激脉冲射流装置的内部流场存在轴心主射流低压区、两个对称的负压区、碰撞高压区,并在靠近碰撞体的腔体处产生漩涡,其外流场和冲击射流流场相似,但不存在射流核心区.

Numerical simulation and experiment on flow fields in underwater self-excited pulse jet device

A series of experiments on underwater self-excited pulse jet are made by using a self-developed test platform and the axial and radial distributions of pressure around an underwater self-excited pulse jet are obtained. Then, the flow fields inside and outside the jet are simulated, the corresponding velocity and pressure distributions are acquired and compared with the experimental data. The results show that obvious low frequency pulses can occur for the self-excited pulse jet under non-submerged condition. Under submerged condition, however, because part of the jet energy is consumed in the submerged water body so much that it is hard for cavitation to form in the chamber and to generate obvious pulse, further the stagnation pressure is reduced significantly. The radial pressure distribution is basically the same in different depths of the water, approximately yields the Gaussian distribution. The axial stagnation pressure is decreased with the increasing distance to the target, and its attenuation characteristic is similar to that for continuous jet and under non-submerged condition, just the decay rate is even faster. A low pressure zone in the jet core, two symmetrical negative pressure zones and a high pressure impinging zone exist in the flow field in the chamber of the underwater self-excited pulse jet device. Vortexes are generated near the bottom casing, and the flow field is similar to the jet flow in the chamber, but without a core.