水下爆炸近壁面流场局部空化形成机理

为深入认识水下爆炸近壁面流场局部空化的形成机理，采用自行研制的转镜式分幅相机，获得了炸药水下爆炸近壁面流场局部空化效应的光学图像，结合数值模拟和Taylor平面波理论、空泡动力学理论，分析了近壁面空化效应的形成过程。结果表明：界面反射的稀疏波作用和水中空化核的膨胀发展是水下爆炸近壁面流场空化效应形成的原因；外界流场压力对空泡初期膨胀运动影响较小，对空泡后期运动行为影响较大；低压环境下不同尺度空泡的运动行为存在较大差异，小尺度空泡（半径小于10μm）在低压环境下处于快速膨胀、溃灭状态，对流场空化影响较小；大尺度空泡（半径大于10μm）可失去稳定性，半径持续增大，对流场空化区的形成影响较大；水中不同尺寸空泡空间分布的随机性可导致空化区成长过程中呈现非规则形状。

On formation mechanism of local cavitation in the near-wall flow field caused by an underwater explosion

In order to deeply understand the formation mechanism of local cavitation in the near-wall flow field caused by an underwater explosion, the optical images showing the local cavitation effect near the wall were obtained by using a self-developed rotating-mirror framing camera with high frequency and high resolution. Numerical simulations were carried out to present the flow-field pressure of shock wave propagation by giving the location of the cavitation area. The Taylor plane wave theory, an efficient method for describing the formation time of local cavitation, was applied to explain the reason that the cavitation did not form in the experimental case 1 that the explosive center was 120 mm from the wall. And the cavitation dynamics theory was used to analyze the local cavitation effect in the experimental case 2 that the explosive center was 80 mm from the wall, by calculating the motion laws of the cavities with different radii under different external environmental pressures. It is indicated that the existence of the rarefaction waves reflected by the interfaces and the expansion of the cavitation nuclei in the water result in the cavitation effects in the near-wall flow field. The external flow-field pressure hardly affects the initial stage of cavitation bubble expansion, but it exerts great influences on the movement behavior of the cavitation bubbles in the later stage. The cavitation bubbles with different sizes will take on different movement behaviors in the low-pressure environment. The cavitation bubbles with the small size less than 10 μm will expand and collapse rapidly in the low-pressure environment so that they have little effects on the flow field cavitation. While the cavitaion bubbles with the large size more than 10 μm may lose the stability, with the result that they have great influences on the flow-field cavition. The random spatial distribution of different-size cavitation nuclei in water is the main reason that the cavitation zone presents an irregular shape during the evolution progress.