群振动气泡的非线性声响应及空化分析

Nonlinear acoustic response of bubbles in a cluster and cavitation analysis of bubble-liquid mixture

在多泡系统中考虑了气泡间次级声辐射和群振动引起的边界振动,进而得到群振动气泡动力学方程。通过逐级近似法对群振动气泡动力学方程进行了非线性分析,得到了二分频和三分频分振动幅值随频率和基频振动幅值变化关系。并基于分频振动产生条件进行了数值分析,发现稳态空化阈值相对较低,且三分频振动只存在于大于三倍气泡共振频率的区间内。利用空化气泡崩溃辐射声强表征空化强度,分析了群振动气泡相关的惯性空化特征,数值分析结果表明:对初始半径相同的气泡,惯性空化气泡能量转换能力要高3个数量级以上,气泡初始半径在3~10μm区域声响应和能量转换能力较强;低频区声波作用下空化气泡的惯性空化阈值约为1 atm(1 atm=101325 Pa);对空化气泡分布区内的气泡,初始半径越大,惯性空化阈值越低。在一定的声作用环境下,调控驱动声波频率和强度可实现空化区域内空化强度的有效调控。

The oscillation of bubbles inside a cluster is affected by many factors,such as the interaction caused by the secondary radiation of neighboring bubbles,the liquid pressure distribution inside the cluster.A model is developed to describe the coupled oscillation of uniform gas bubbles in a cluster by considering the pulsation of the boundary of the cluster and the secondary radiation of bubbles.Based on the nonlinear analysis of the model by use of progressive approximation,the 1/2 and 1/3 subharmonic responses are investigated.The stable cavitation threshold can be obtained by use of the activating condition of 1/2 subharmonic vibration,and a small value of the threshold can be got for a stable oscillating bubble-liquid system.The 1/3 subharmonic responses can be activated in the region of over three times of resonant frequency.In order to explore the inertial cavitation of a bubble cluster,the radiation acoustic intensity of cavitation bubble in the collapse phase is introduced to describe the cavitation intensity.The numerical analysis results show that the energy transfer ability of the inertial cavitation bubble is three order higher than the stable oscillating bubble.For cavitation bubbles of 3~10μm initial radius,there are higher acoustic energy transfer level and the inertial cavitation threshold is about 1 atm in the low-frequency region.The larger bubble has a lower inertial cavitation threshold relatively.Therefore,the cavitation intensity can be controlled by mediating the amplitude and frequency of the ultrasound wave in the cavitation field.