近固壁微米尺度空泡溃灭的数值研究

Numerical Simulation of Micrometer-Sized Bubble Collapse near a Rigid Boundary

考虑空泡表面张力、液体黏性和气体可压缩性,采用VOF多相流模型对近固壁微米尺度空泡在静止流场溃灭过程进行了数值研究.获得了近固壁空泡溃灭过程的流场细节,分析了空泡与固壁的无量纲距离γ对空泡溃灭过程动力特性的影响,并揭示了不同γ条件下的固壁空蚀破坏机理.计算结果表明:随着γ的减小,泡心向固壁移动的趋势明显,射流形成前空泡上部高压区内压力减小,空泡溃灭时间延长,最大射流速度减小.模拟结果验证了空泡溃灭将产生冲击波和高速微射流,二者均会在固壁面产生脉冲压力,其是造成壁面损伤的两种主要原因.参数γ对固壁的空蚀破坏机理有重要影响.与微射流机制相比,以冲击波机制为主的空蚀破坏更显著.微射流冲击固壁的作用半径为10μm左右,将引起固壁"点"蚀坑的出现.当γ=2.0时,冲击波扫掠壁面的范围相对较广,有效作用半径约为1 mm,其导致固壁产生较大圆形蚀坑,且中心空蚀严重.

Collapse of a single micrometer-sized cavitation bubble near a rigid boundary was numerically simulated by using volume of fluid (VOF)multiphase model with considering surface tension of vapor-liquid interface,liquid viscosity and compressibiIity of gas in bubble.The detailed flow field was obtained during a bubble collapsed near to the wall and the effect of the non-dimensional stand-off parameter ),on the collapse behavior of bubble was discussed. Moreover,the cavitation erosion on the wall was revealed for different γ.The computational results show that the bubble center approached the wall,the pressure decreased in the high pressure zone above the bubble prior to formation of jet, collapse time delayed and the maximum jet velocity decreased as γ decreased.The simulated results verified that the bubble collapse near the wall can produce shock wave and micro jet,both of which can make the wall subjected to an impulse pressure.The cavitation-erosion mechanism on the wall was significantly determined by the stand-off parameter γ.Compared with micro jet,shock wave had a more remarkable cavitation damage on the wall.The action radius of micro jet on the wall was about 10μm,which led to the spot corrosion pits.The area swept by shock wave was relatively wide and the effective action radius on the wall was about 1mm for γ=2.0,which led to the annular corrosion pits with a seriously eroded center.