基于多相流LBM-VOF联合模式的水泵进水池漩涡流研究

This study focuses on some details and a mechanism for air-liquid two-phase vortex flows at free surface and vapor-liquid two-phase cavitating flows caused by wall-attached vortices in pump suction sumps using theoretic, parallel and testing techniques. Based on sub-grid scale models for large eddy simulation (LES) and mesoscopic multi-scale expansion method, LBM (lattice Boltzmann method) models combined with LES for air-liquid two-phase flows at the free surface are developed using LBM for single-component two-phase flows and VOF (volume of fluid) interface-reconstructed models, and then phase transitions with LBM for vapor-Liquid two-phase flows are described by equation of state for matter so that LBM models combined with LES for vapor-liquid two-phase cavitating flows caused by wall-attached vortices are proposed. High-resolution to capture the free surface and high-accuracy parallel methods are studied and designed for LBM, and thus a framework is formulated to quantitatively represent evolution processes of vortex flows at the free surface and a transformation regulation of mass and momentum caused by wall-attached vortex cavitations, which can be used to effectively and precisely simulate evolutions of various vortex flows in pump suction sumps. Finally, moedern high speed photography and visual particle image velocimetry (PIV) techniques are used to observe and measure experimentally various characteristic flows in pump suction sumps. The experimental data are used to validate the rationality and the reliability of the above-mentioned models and numerical schemes. In short, this investigation aims at putting forth a new technique for free-surface flows and vortex cavitations.

拟采用理论分析法、并行算法和现代测试手段，深入研究水泵进水池的自由表面气-液两相漩涡流和附壁漩涡空化两相汽-液流的若干细节及机理。基于大涡模拟(LES)亚格子模型和介观多尺度展开方法，利用单组分两相流格子Boltzmann方法(LBM)和VOF(volume of fluid)界面重构模型，发展自由表面气-液两相流LBM和LES的联合模式，然后，采用物质状态方程来描述汽-液两相流LBM相变，发展漩涡空化汽-液两相流LBM和LES计算模式。研究设计高分辨率自由界面捕捉算法和高精度LBM并行方法，建立一套方法来定量描述自由表面漩涡的动态演变和漩涡空化相变的质量和动量的转化规律，精确高效地模拟进水池各类漩涡的演变规律。最后，利用现代高速摄影、可视PIV来实验观测和测量进水池内流动特性，通过一系列实验数据验证上述模型和算法的合理性和可靠性。本研究将为自由表面流动和漩涡空化流动研究提供一种新方法。

进水池是通过进水管直接从中取水的水工建筑物，其内部的不良流态往往是引发水泵机组振动、汽蚀和效率降低等一系列问题的主要原因。针对不同流速条件下，利用现代高速摄影、PIV (Particle Image Velocimetry)实验研究了不同的后壁距、临界淹没水深、水中空气含量对进水池内流态的影响，发现了在喇叭管入口靠近后壁面附近出现了速度曲线分叉现象和后壁距与漩涡的数量和强度关系紧密；针对不同压力的封闭式进水池，实验研究了自由液面漩涡及液下漩涡数量、速度分布、涡量随压力变化的演化过程，发现了自由液面漩涡与液下涡的个数随着压力绝对值的升高而升高，概率统计分析了列各测量面上的流动形态漩涡形态并划分了无涡区、单涡区、过渡区、多涡区等四种涡区。基于大涡模拟(Large Eddy Simulation，LES)亚格子模型和介观多尺度展开方法，利用单组分两相流格子Boltzmann方法(Lattice Boltzmann Method，LBM)和VOF(Volume Of Fluid)，发展自由表面的LBM和LES的联合模式，然后，采用物质状态方程来描述液相相变，发展了空化两相流LBM的Carnahan-Starling-Shan-Chen联合模式。利用LBM-LES-VOF联合模型很好地预测到了进水池内湍流的数量不一的自由液面漩涡、侧壁涡、后壁涡及底面涡，预测的速度分布和涡旋位置与物理模型的实验数据吻合较好。利用空化流Carnahan-Starling-Shan-Chen模型成功地预测了三维气核空化的发生发展和收缩溃灭及复现过程，计算结果符合能障理论，并系统地分析了温度、气核内外压差和气核初始半径等影响。采用MPI (Message Passing Interface)消息传递接口和CUDA (Compute Unified Device Architecture)技术，通过C++开发了相关并行计算程序，研究分析了并行进程数的时间最短、加速比最大、具有较高通信等数值并行效率。本研究通过一系列实验数据验证上述模型和算法的合理性和可靠性，将为自由表面流动和漩涡空化流动研究提供一种新方法。