通气空泡流特性及减阻机理的多尺度研究

Experimental research have proved that high efficent drag reduction (over 90%) could be achieved for ventilated cavitating underwater vehicle. However, due to the accompanied multiscale, strong turbulent and highly non-linear phenomenas such as the free-surface fluctuation, free-surface air entrainment and unstable gas leakage during the formation of ventilated cavity, the influence of ventilated cavity acting on the hydrodynamics, stability and noise for underwater vehicle requires further research. In this project, fundamental study on the flow characteristics and drag reduction mechanisms for the ventilated cavitating flow is carried out using incorperated experimental, numerical and theoretical methods. Multiscale simulation model for gas-liquid flow is established to predict the detail flow characteristics. Meanwhile, the cavity shape and bubbly flow parameters is measured using the high speed camera and partical/droplet image analysis (PDIA) system in order to validate the numerical model. Furthermore, the free-surface air entrainment mechanism for ventilated cavity is explored, and the interactions between macroscale cavity, microscale bubbles and the vehicle body are revealed. The variation of cavity shape and bubbly flow parameter distributions is summarized, based on which the theoretical model to predict the cavitating vehicle performance parameters is established. The obtained results will provide theoretical guidance for achieving high velocity, stability, and low noise of the ventilated cavitating underwater vehicle.

实验研究表明通气空泡可以实现水下航行体高效减阻（减阻90%以上），然而，由于通气空泡形成过程中存在界面波动、自由面掺气、非定常泄气等多尺度、高湍流度、高度非线性现象，其对航行体水动力、稳定性和噪声特性的影响仍有待深入研究。本项目拟采用实验研究、数值模拟和理论分析相结合的方法对通气空泡流特性及其减阻机理进行多尺度研究。建立气液两相流多尺度数值计算模型对精细流场结构进行预测，同时，采用高速摄影仪和颗粒/液滴图像分析（PDIA）系统对空泡形态和气泡流参数等进行准确测量，验证数理模型，进而分析通气空泡自由面掺气机理，揭示大尺度空泡、微尺度气泡及航行体间相互作用规律，总结空泡形态变化和气泡流参数分布特性，建立与航行体水动力和噪声特性相关的性能参数预估模型，为通气空泡航行体的高速、稳定、低噪运行提供理论指导。

实验研究表明通气空泡可以实现水下航行体高效减阻（减阻90%以上），然而，由于通气空泡形成过程中存在界面波动、自由面掺气、非定常泄气等多尺度、高湍流度、高度非线性现象，其对航行体水动力、稳定性和噪声特性的影响仍有待深入研究。本项目综合运用数值模拟、理论分析和数值模拟相结合的方法开展了通气空泡流特性及其减阻机理的多尺度研究。建立了考虑湍流作用、表面张力、重力作用的自由面掺气过程理论计算模型；基于欧拉-欧拉多流体模型和VOF界面追踪方法建立了气液两相多尺度数值计算模型，实现了自由面掺气过程中大尺度气液界面形成、微尺度气泡生长与扩散过程的耦合计算；基于OpenFOAM平台和序列近似优化算法建立空化模型参数辨识方法，计算精度提高12%；基于多尺度数值计算模型开展了水跃流和局部通气空泡掺气过程数值模拟，准确捕捉了掺气过程中大尺度气液界面演化过程，揭示了空泡与微气泡耦合减阻机理，提出通过合理设计尾部外形有效降低压阻系数的方法；提出了一种新型带动力超空泡试验方法，采用空化水翼和小水线面双体船外形设计，具有航速高、试验不受航迹和尺寸约束、易于发射和回收等特点。项目研究成果对于深入揭示多相湍流演化机理，促进空泡减阻技术的发展具有重要意义。