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Effect of stand-off distance on “counterjet” and high impact pressure by a numerical study of laser-induced cavitation bubble near a wall
International Journal of Multiphase Flow ( IF 3.8 ) Pub Date : 2021-05-27 , DOI: 10.1016/j.ijmultiphaseflow.2021.103706
Ju Zhang

In experiments of the collapse and rebound of a laser-produced cavitation bubble near a wall, a so-called “counterjet”, i.e., a jet in the direction away from the bubble and the wall, was typically observed during the rebound phase for a certain range of stand-off distances. It was previously suggested that a mechanism for the formation of the counterjet might be cavitation inception that follows the self-penetration of the jet torus shock wave. Numerical simulations in the current work show that this counterjet may in fact be part of the bubble spiral trailing behind the main part as the bubble is distorted by the ring vortex and becomes toroidal in shape after the initial collapse. Since the spiral is trailing behind the main bubble, it appears to be a jet in the direction away from the bubble and the wall, giving the impression of the formation of a counterjet. However, the simulations show that the velocities in the spiral are also towards the wall. The effects of phase transition on various aspects of bubble collapse dynamics are also examined. It is found that the experimental bubble-wall distance evolution can only be better captured through the inclusion of phase transition modeling. Without phase transition, the bubble-wall distance history in the simulations diverges from the experimental one upon the first collapse. After these validations, the effects of stand-off distance on the impact pressure are studied systematically with results compared with experiments. It is found that the largest impact pressures can be as high as 1–2 GPa as a result of the strong focus of a nearly spherical shock onto the symmetry axis and along the wall that occurs when the stand-off distances are low with Ho/Ro<0.1. The impact pressure of 0.1 GPa at Ho/Ro<0.7 on the other hand is found to be the result of the focus of the ring-vortex-focusing shock onto the symmetry axis. Both the magnitude of the impact pressure and the respective stand-off distance range are consistent with previous experimental results.



中文翻译:

通过壁面附近激光诱导空化气泡的数值研究,距离对“反喷”和高冲击压力的影响

在靠近壁面的激光产生的空化气泡坍塌和回弹的实验中,通常在回弹阶段观察到所谓的“反射流”,即远离气泡和壁面方向的射流。一定范围的隔离距离。先前有人提出,形成反射流的机制可能是随着射流环面激波的自穿而产生的空化开始。当前工作中的数值模拟表明,由于气泡被环形涡旋扭曲并在初始坍塌后变成环形,因此这种反射流实际上可能是尾随在主要部分后面的气泡螺旋的一部分。由于螺旋尾随在主气泡的后面,因此它似乎是朝着远离气泡和壁的方向喷射,给人一种形成反喷的印象。然而,模拟显示螺旋中的速度也朝向壁。还研究了相变对气泡破裂动力学各个方面的影响。发现只有通过包含相变模型才能更好地捕获实验气泡壁距离演化。在没有相变的情况下,模拟中的气泡壁距离历史在第一次坍塌时与实验中的不同。在这些验证之后,系统地研究了间隔距离对冲击压力的影响,并将结果与​​实验进行了比较。H/电阻<0.1. 冲击压力0.1 GPa at H/电阻<0.7另一方面,发现是环涡聚焦激波聚焦在对称轴上的结果。冲击压力的大小和各自的间隔距离范围都与之前的实验结果一致。

更新日期:2021-06-07
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