基于泡间相互作用的空化模型研究及实验验证

Cavitation is a paramount topic of hydraulic machinery research, which could induce great pressure fluctuation and instability, affecting safe, stable and efficient operation of hydraulic systems. In this project, a cavitation model will be developed for the bubble cloud with high void fraction in order to reveal the characteristics of its nonlinear oscillations and associated pressure fluctuation. Theoretical investigation, numerical simulation and experimental study will be combined together to fulfill this target. For theoretical analysis, equation of bubble wall motion will be extended through considering terms representing bubble-bubble interaction and then the analytical expression of the force between oscillating bubbles will be obtained through solving above equation. Parameter analysis will be performed in great details to find the control parameters. For experimental study, combining PIV, high-speed camera and high-accuracy pressure sensor, the dynamic interacting process between multi-bubbles will be imaged and recorded together with their relative motion and fluid flow surrounding bubbles. The magnitude and direction of the interaction force between bubbles will be deduced based on the experimental data to verify the analytical modeling. Based on above results, the current cavitation model based on volume fraction transportation equation will be improved through incorporating force caused by the bubble-bubble interaction. And the evaporation term and condensation term in previous model will be revised accordingly. The new cavitation model will be verified using classical experimental data of hydrofoil cavitation.

空化是水力机械研究领域的核心问题，其引起的压力脉动和空蚀破坏严重影响水力机械及其系统的安全、稳定和高效运行。本项目拟发展针对高体隙率空化流的理论模型，研究其引起的压力脉动和非线性振荡的主要特征。研究方法上，本项目拟采用理论分析、数值模拟和实验研究相结合的方式进行。理论分析方面，将泡间相互作用力引入到泡动力学基本方程中，推导出准确描述泡间相互作用力的表达式并对相关重要物理参数进行详细分析。采用粒子图像测速技术，高速摄影和压力脉动测量相结合的方法，测量相互作用的多个空化泡的动态振荡过程，相对运动及周围流场的详细细节，并基于上述测量结果推断泡间相互作用力的大小和方向，用以验证理论表达式。基于上述成果，通过将泡间相互作用力表达式引入到体积分数输运方程空化模型中对现有的空化模型进行进一步改进，修正输运方程中表征空化泡产生和消亡的蒸发项和冷凝项的表达式，并选取有代表性的翼型空化实验数据对上述空化模型进行详细验证。

空化泡间相互作用是空化研究领域的核心问题之一，其对空化泡的动力学行为、空化引起的空蚀破坏及压力脉动均具有显著的影响。本项目采用理论分析、数值模拟和实验研究相结合的研究方法，获得了以下研究成果：揭示了两个空化泡的泡间相互作用对于空化泡动力学行为的影响，尤其是对于空化泡的溃灭、移动、射流等现象的影响，清晰展示了空化泡距离较近时泡间相互作用引起的聚并行为；理论分析和数值模拟方面，阐述了泡间相互作用力产生的根源及物理机制，发现空化泡半径等核心参数以及谐波、次谐波等非线性现象可显著影响泡间相互作用力的大小甚至方向。