气液旋转流场中曲面壁面上液膜破碎行为研究

The liquid film on the circular wall of gas-liquid vane-type separators is unstable due to the shear effect of the swirling gas and impact of the liquid droplets. Droplet entrainment happens, which results in significant decrease of separation efficiency and is challenging for the designers. Reports on the stability and broken-up behavior of the liquid film on the curved wall of channels whose main steam is swirling, are rare. Therefore, in present study, the behaviors of the liquid film on curved wall are investigated. A transparent typical swirling channels representing the channels inside separator is developed with air-water as the working fluid. The velocity of air inside the test section are measured by Laser Doppler Velocimetry (LDV), while the behavior of the liquid film on the curved wall are recorded by high speed camera. Meanwhile, the thickness of the film on the curved wall is measured by two-parallel electronic conductance probes. The typical dynamic features of the liquid film and droplets are obtained, for example, film cavitation, droplet bouncing, droplet spreading and droplet splashing. The region for every typical features are specified. By using proper turbulent model and liquid-gas interface capturing method, numerical simulation for typical dynamic behavior of the liquid film on curved wall, swirling gas stream and droplets are carried out. Thereby, detailed velocity and phase distribution are obtained and analyzed. Moreover, the forces on the liquid film on curved wall and droplets are analyzed. The key non-dimensional parameters and inception criterion for the stability and broken-up behavior of the film on curved wall are deducted. The non-dimensional inception criterion of droplet entrainment is developed with the assistance of the force balance analysis. The size of the new born droplets will be recorded by high speed camera. The size and the amount of new born droplets will be correlated to non-dimensional parameters. These correlations with the droplet entrainment criterion could be used for developing models for predicting the film thickness and separation performance of the swirl-vane separator. Through these work, the mechanism of film broken-up and droplet entrainment for films on curved wall with a swirling main stream is obtained and the correlations could be used for developing the models for the analysis of the performance of gas-liquid vane-type separator.

气液旋叶分离器筒体圆形壁面的液膜在旋转气体剪切和液滴撞击下极易发生破裂，造成液滴二次夹带的现象，导致分离性能急剧下降，是气液旋叶分离器设计的主要挑战之一。目前针对旋转流场中曲面壁面液膜行为的研究匮乏。本项目以在旋转气流与液滴碰撞作用下曲面壁面液膜破碎行为为对象开展研究，构建典型旋转通道可视化实验模型，采用激光多普勒测速、可视化高速摄像和平行电导探针测量技术，获得旋转气流和液滴作用下曲面壁面液膜凹陷、液滴反弹、液滴延展、液滴飞溅等典型现象及分区边界，遴选恰当的湍流模型和气液界面捕捉模型对典型现象展开CFD数值模拟，获得典型现象详尽的速度场和相分布。进一步开展液膜理论动力学分析，推导表征曲面液膜稳定性和液膜破碎的无量纲准则数，建立典型现象分区的无量纲准则边界和二次液滴粒径、夹带量的无量纲关系式。本研究揭示旋转流场中曲面壁面液膜破碎液滴夹带的机理，为旋叶分离器内气液分离分析提供理论基础。

气液旋叶分离器筒体圆形壁面的液膜在旋转气体剪切和液滴撞击下极易发生破裂，造成液滴二次夹带的现象，导致分离性能急剧下降，是气液旋叶分离器设计的主要挑战之一。本项目针对对气液旋转流场中旋转气流或液滴碰撞作用下曲面壁面液滴飞溅和液膜破碎现象展开实验、动力学理论分析和数值模拟研究。通过液滴撞击干湿壁面可视化试验和小液量旋流作用液膜破碎可视化实验方法发现旋转气流充分发展区液膜不稳定主要存在丝带式破碎和液滴撞击湿壁的飞溅两种机制，旋转气流发展区主要存在壁面液膜不稳定主要是袋式破碎和丝带式破碎两种机制，而液滴撞击存在多种方向的铺展破碎行为，液滴撞击倾斜微针湿表面能够抑制液滴飞溅。通过图片提取技术获得了破碎飞溅形成二次液滴的粒径和破碎边界数据，结合旋流液膜力平衡分析获得液滴飞溅发生边界，形成现象分区特别是破碎发生无量纲准则边界，建立描述二次液滴夹带量和二次液滴粒径分布特性关系式。同时建立了采用单相表面自由能模型模拟气液界面和考虑重力、离心力的Guo外力模型形成适用模拟旋流中旋流液滴撞击液膜的格子玻尔兹曼模型，结合CFD数值模拟方法，获得液滴撞击液膜的精细特征以及旋气流详细的速度场和相分布信息。进一步基于试验和CFD数值模拟获得的旋叶下游气相场具有的双向涡特征，构造布拉格-霍桑方程（BHE）方程流函数实现旋叶下游双向涡气相流场的理论求解，通过离散液滴粒子受力模型获得液滴轨迹，并结合液膜破碎液滴夹带临界边界关系式和夹带量关系式，构建具有液滴夹带效应的旋叶分离器分离性能预测模型。通过考虑液滴夹带效应。本课题开展有助于深入认识旋气流和液滴撞击作用下液膜行为特征，揭示了旋转流场中曲面壁面液膜破碎机理，阐明影响旋流液滴夹带和气液分离主要机制，建立了液膜破碎液滴飞溅边界和粒径关系式，开发了双向涡特征和具有液滴夹带效应的分离器性能预测模型，为旋叶分离器内气液分离分析和分离器优化提供理论基础和分析工具。