National Institute of Cancer Research, National Health Research Institutes, Tainan 70456, Taiwan.
Ann Biomed Eng. 2010 Oct;38(10):3162-72. doi: 10.1007/s10439-010-0070-y. Epub 2010 May 20.
When studying mechanical heart valve cavitation, a physical model allows direct flow field and pressure measurements that are difficult to perform with actual valves, as well as separate testing of water hammer and squeeze flow effects. Movable rods of 5 and 10 mm diameter impinged same-sized stationary rods to simulate squeeze flow. A 24 mm piston within a tube simulated water hammer. Adding a 5 mm stationary rod within the tube generated both effects simultaneously. Charged-coupled device (CCD) laser displacement sensors, strobe lighting technique, laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and high fidelity piezoelectric pressure transducers measured impact velocities, cavitation images, squeeze flow velocities, vortices, and pressure changes at impact, respectively. The movable rods created cavitation at critical impact velocities of 1.6 and 1.2 m/s; squeeze flow velocities were 2.8 and 4.64 m/s. The isolated water hammer created cavitation at 1.3 m/s piston speed. The combined piston and stationary rod created cavitation at an impact speed of 0.9 m/s and squeeze flow of 3.2 m/s. These results show squeeze flow alone caused cavitation, notably at lower impact velocity as contact area increased. Water hammer alone also caused cavitation with faster displacement. Both effects together were additive. The pressure change at the vortex center was only 150 mmHg, which cannot generate the magnitude of pressure drop required for cavitation bubble formation. Cavitation occurred at 3-5 m/s squeeze flow, significantly different from the 14 m/s derived by Bernoulli's equation; the temporal acceleration of unsteady flow requires further study.
在研究机械心脏瓣膜空化时，物理模型允许直接进行流场和压力测量，而这在实际瓣膜中很难实现，并且可以单独测试水锤和挤压流效应。直径为 5 和 10 毫米的可移动棒撞击相同尺寸的固定棒，以模拟挤压流。管内的 24 毫米活塞模拟水锤。在管内添加 5 毫米的固定棒会同时产生这两种效应。电荷耦合器件 (CCD) 激光位移传感器、频闪照明技术、激光多普勒测速 (LDV)、粒子图像测速 (PIV) 和高保真压电压力传感器分别测量冲击速度、空化图像、挤压流速度、涡旋和冲击时的压力变化。可移动棒在 1.6 和 1.2 m/s 的临界冲击速度下产生空化；挤压流速度分别为 2.8 和 4.64 m/s。孤立的水锤在 1.3 m/s 的活塞速度下产生空化。组合活塞和固定棒在 0.9 m/s 的冲击速度和 3.2 m/s 的挤压流下产生空化。这些结果表明，挤压流单独导致空化，特别是在接触面积增加时，冲击速度更低。水锤单独也会导致更快的位移空化。这两种效应是相加的。涡心的压力变化仅为 150 毫米汞柱，这不能产生形成空化气泡所需的压力降幅度。空化发生在 3-5 m/s 的挤压流中，与伯努利方程得出的 14 m/s 显著不同；非定常流的时间加速度需要进一步研究。
