Yu Qidong, Ma Xiaojian, Xu Zhicheng, Zhao Jing, Wang Dapeng, Huang Zhenwei
Department of Research and Development, China Academy of Launch Vehicle Technology, Beijing 100076, China.
Department of Research and Development, China Academy of Launch Vehicle Technology, Beijing 100076, China.
Ultrason Sonochem. 2021 Mar;71:105396. doi: 10.1016/j.ultsonch.2020.105396. Epub 2020 Nov 13.
The objective of this paper is to numerically investigate the thermodynamic effect during bubble collapse near a rigid boundary. A compressible fluid model is introduced to accurately capture the transient process of bubble shapes and temperature, as well as corresponding pressure, and velocity. The accuracy of the numerical model is verified by the experimental data of bubble shapes, and Keller-Kolodner equation as well as its thermodynamic equation. The results show that a bubble near the rigid boundary presents high-speed jet in collapse stage and counter jet in rebound stage, respectively. In the collapse stage, the bubble margin will shrink rapidly and do the positive work on the compressible vapor inside the bubble, then a significant amount of heat will be generated, and finally the generation of high-speed jet drives the low-temperature liquid outside the bubble to occupy the position of high-temperature vapor inside the bubble. In the rebound stage, the counter jet moving away from the rigid boundary takes part of heat away from the sub-bubble, which avoids the external work of the expansion of the sub-bubble and the temperature reduction caused by the dissipation effect of the vortex structure. In addition, the initial standoff has a significant effect on the thermodynamics of bubble oscillation. The temperature keeps increasing with the increase of the initial standoff in the collapse stage, while it shows a downward trend with the increase of the initial standoff in the rebound stage. That's because the high-speed jet and counter jet of bubble gradually disappear when the initial standoff increases, which is the important reason for the opposite evolution trend of temperature in collapse and rebound stage.
本文的目的是对刚性边界附近气泡坍缩过程中的热力学效应进行数值研究。引入了可压缩流体模型，以准确捕捉气泡形状、温度以及相应压力和速度的瞬态过程。通过气泡形状的实验数据、凯勒 - 科洛德纳方程及其热力学方程验证了数值模型的准确性。结果表明，刚性边界附近的气泡在坍缩阶段和反弹阶段分别呈现高速射流和反向射流。在坍缩阶段，气泡边缘会迅速收缩，并对气泡内的可压缩蒸汽做正功，进而产生大量热量，最终高速射流的产生驱使气泡外的低温液体占据气泡内高温蒸汽的位置。在反弹阶段，远离刚性边界的反向射流将部分热量从子气泡带走，避免了子气泡膨胀的外部做功以及涡旋结构耗散效应导致的温度降低。此外，初始间距对气泡振荡的热力学有显著影响。在坍缩阶段，温度随初始间距的增加而持续升高，而在反弹阶段，温度则随初始间距的增加呈下降趋势。这是因为当初始间距增大时，气泡的高速射流和反向射流逐渐消失，这是坍缩和反弹阶段温度呈现相反演变趋势的重要原因。
