Lim W L, Chew Y T, Low H T, Foo W L
Department of Mechanical Engineering, Faculty of Engineering, 9 Engineering Drive 1, National University of Singapore, 117576, Singapore, Singapore.
J Biomech. 2003 Sep;36(9):1269-80. doi: 10.1016/s0021-9290(03)00161-1.
In this study, the closing dynamics of two impinging rods were experimentally analyzed to simulate the cavitation phenomena associated with mechanical heart valve closure. The purpose of this study was to investigate the cavitation phenomena with respect to squeeze flow between two impinging surfaces and the parameter that influences cavitation inception. High-speed flow imaging was employed to visualize and identify regions of cavitation. The images obtained favored squeeze flow as an important mechanism in cavitation inception. A correlation study of the effects of impact velocities, contact areas and squeeze flow velocity on cavitation inception showed that increasing impact velocities results in an increase in the risk of cavitation. It was also shown that for similar impact velocities, regions near the point of impact were found to cavitate later for those with smaller contact areas. It was found that the decrease in contact areas and squeeze flow velocities would delay the onset and reduce the intensity of cavitation. It is also interesting to note that the squeeze flow velocity alone does not provide an indication if cavitation inception will occur. This is corroborated by the wide range of published critical squeeze flow velocity required for cavitation inception. It should be noted that the temporal acceleration of fluid, often neglected in the literature, can also play an important role on cavitation inception for unsteady flow phenomenon. This is especially true in mechanical heart valves, where for the same leaflet closing velocity, valves with a seat stop were observed to cavitate earlier. Based on these results, important inferences may be made to the design of mechanical heart valves with regards to cavitation inception.
在本研究中，对两根碰撞杆的闭合动力学进行了实验分析，以模拟与机械心脏瓣膜关闭相关的空化现象。本研究的目的是研究关于两个碰撞表面之间的挤压流动以及影响空化起始的参数的空化现象。采用高速流动成像来可视化和识别空化区域。所获得的图像表明挤压流动是空化起始的一个重要机制。对冲击速度、接触面积和挤压流动速度对空化起始影响的相关性研究表明，增加冲击速度会导致空化风险增加。还表明，对于相似的冲击速度，接触面积较小的碰撞点附近区域空化较晚。发现接触面积和挤压流动速度的减小会延迟空化的开始并降低空化强度。同样有趣的是，仅挤压流动速度并不能表明是否会发生空化起始。这一点得到了已发表的空化起始所需临界挤压流动速度的广泛范围的证实。应该指出的是，文献中经常忽略的流体的时间加速度，对于非定常流动现象的空化起始也可能起重要作用。在机械心脏瓣膜中尤其如此，在相同瓣叶关闭速度的情况下，观察到带有座止动装置的瓣膜空化更早。基于这些结果，可以对机械心脏瓣膜在空化起始方面的设计做出重要推断。
