壁面处气泡在静止流场和高速水流中溃灭过程的计算仿真

Simulation of Vapor Bubble Collapsing Near or On Wall in Stationary Water or High Speed Water

通过数值仿真计算,模拟近壁面以及附壁面气泡在静止流场和高速水流中的溃灭过程,研究气蚀作用机理.结果表明:气泡与壁面的距离和水流的速度影响其溃灭时间;附壁面气泡在高速水流中完全溃灭的时间最短,而在静止流场中最长,远离壁面将增加气泡的不稳定性;当气泡距离壁面一定距离溃灭时,射流不能直接作用于壁面,壁面承受冲击波的最大压力远小于气泡溃灭中心的压力;当气泡溃灭中心在壁面时,射流直接作用于壁面产生微小而严重的点破坏,而冲击波则使材料产生交变应力,造成环形破坏;当气泡在高速水流中溃灭时将产生逆流斜向射流,这可能是水力机械过流部件产生鱼鳞坑和波纹状破坏的主要原因.

Collapse processes of a vapor bubble which was near or on the wall under the condition in stationary water or high speed water were simulated by numerical calculation. The results show that the stability of a bubble was influenced by the distance between the bubble and the wall as well as the flow velocity. The collapse time of the bubble on the wall was shortest in the high speed water and longest in the stationary water. The instability of the bubble was increased when it was apart from the wall. When a bubble collapsed at a certain distance to the wall, the jet could not impact the wall directly so the wall suffered only from the shock wave. Moreover, the pressure to the wall was less than the maximum pressure generated in the time of the bubble collapsed completely due to the rapid attenuation of the shock wave. When the collapse center was just on the wall, the micro pit damage was produced by jets impacting the wall directly and the ring damage was formed due to the alternate stress generated by the shock waves. The bevel jet was generated contrary to the flow direction when the bubble collapsed in the high speed water, which may cause the ripple and fish-scale pit damage on the transition parts of many hydraulic systems.