近壁声空泡溃灭微射流冲击流固耦合模型及蚀坑反演分析

超声场下液体环境中近壁空泡溃灭会产生强烈的微射流,为探究微射流冲击壁面流固耦合效应,利用流体力学及冲击动力学,考虑了率相关的J-C材料本构模型,建立并分析了微射流冲击壁面流固耦合三维模型,并通过超声空化试验和基于球形压痕试验理论的反演分析进行了验证。结果表明:微射流冲击下材料表面出现微型凹坑,凹坑深度由微射流速度和微射流直径共同决定且随其增大而增大,凹坑直径主要与微射流直径正相关,而凹坑径深比则主要与微射流速度负相关;壁面压强基本呈对称分布且最大压强出现在微射流冲击边缘;超声空化试验验证了微射流冲击下材料表面出现的微型凹坑,反演分析方法表明,在16~18的径深比下,微射流冲击强度为420~500MPa,对应的微射流速度为310~370m/s。试验及反演分析结果与理论分析结果相符,验证了流固耦合模型及反演分析方法的合理性及准确性,为后续工程应用中空化强度、微射流速度等的控制提供了理论参考。

Fluid-solid coupling model of micro-jet impact from acoustic cavitation bubble collapses near a wall and pit inversion analysis

Bubble collapse near a wall will generate strong micro-jet in a liquid environment under ultrasonic field. To explore the fluid-solid coupling effect of micro-jet impinging on a wall, hydrodynamics and impact dynamics were employed, and the J-C rate correlation material constitutive model was applied, then a three-dimensional fluid-solid coupling model of micro-jet impact on a wall was established and analyzed numerically based on the Euler-Lagrange coupling method. Finally, an ultrasonic cavitation test and inversion analysis based on the theory of the spherical indentation test were conducted for validation. Pit depth is decided jointly by micro-jet velocity and micro-jet diameter, and increases with their increases, while the ratio of diameter to depth of a pit is negatively correlated with the micro-jet velocity. Wall pressure distribution is mostly symmetric and the maximum pressure appears on the edge of micro-jet impinging. The maximum wall pressure clearly increases with the micro-jet velocity. The increase of the pressure can lead to the increase of the shock wave intensity and velocity in liquid, which can reach 682 MPa and 2 435 m/s, respectively,when the micro-jet velocity is 479 m/s. Micropits appearing on the material surface impacted by micro-jet were demonstrated by ultrasonic cavitation test, and the pits’ ratio of diameter to depth vary from 16 to 68. Inversion analysis results indicate that equivalent stress, equivalent strain of the pit and impact strength, velocity of the micro-jet are closely related with the ratio of diameter to depth of the pit. When it is 16-68, the micro-jet impingement strength is 420-500 MPa, and the corresponding micro-jet velocity is 310-370 m/s. Test and inversion analysis results are consistent with the theoretical analysis, which verifies the rationality and accuracy of a fluid-solid coupling model considering the J-C rate correlation material constitutive model and inversion analysis method. This work provides a theoretical reference for the control of cavitation intensity and micro-jet velocity in the following engineering applications.