泡状入流条件下离心泵叶轮内气泡滞留动力学机理及模型

When the centrifugal pump operates under the bubble flow inlet, the bubbles may aggregate around the impeller shaft in the form of big bubbles or air mass, and will stagnate in the impeller channel. Based on this phenomenon, a new concept named “bubble stagnation” is proposed in this project. The bubble stagnation affects the pump performance and even results in the surging and gas lock of the pump. However, the dynamic mechanism of the bubble stagnation in the impeller is not yet clear and an appropriate model to predict the bubble stagnation is still to be developed. In the present project, the process, the dynamic mechanism and the prediction model of the bubble stagnation in the impeller are investigated through experimental and numerical methods. The dynamic behavior of bubbles flowing in the impeller is investigated, the collision, break up and coalescence of bubbles and their motion in the impeller channel are observed and analyzed. We establish a numerical simulation method to accurately obtain the gas-liquid interface in the impeller channels, and by which the reasons of bubble stagnation are explored; then corresponding mechanisms are revealed. According to the process and mechanisms of the bubble stagnation in the channel, we determine the dimensionless parameters those affect the bubble stagnation; obtain the dynamic conditions of the bubbles to be stagnated, and develop a model to predict the bubble stagnation. The results provide theoretical support for the optimal design and safe working of the turbomachinery, including the multiphase flow pump and the reactor coolant circulating pump, and also contribute to the interdisciplinary research between the fluid machinery and the multiphase flow thermal physics.

泡状入流条件下，气泡可能在离心泵叶轮转轴附近以大气泡或气团的形式聚集，进而滞留在叶轮流道内，基于这一现象，申请人提出“气泡滞留”这一新概念。叶轮流道内的气泡滞留直接影响泵的性能，严重情况下引起泵喘振和气锁，然而气泡滞留的动力学机理尚未明确，亦缺乏合适的预测模型。本项目采用机理实验和数值模拟相结合的方法，从叶轮流道内气泡滞留过程、动力学机理、预测模型三个层次开展研究。系统考查气泡在离心泵叶轮流道内的动力学行为，探究气泡碰撞、破碎、聚并等形态变化和运动规律，掌握气泡滞留的过程；建立准确捕捉叶轮流道内气液相界面的数值模拟方法，结合机理实验，查明气泡滞留原因，揭示气泡滞留机理；进而确定影响气泡滞留的无量纲参数，获得气泡滞留的动力学条件，建立气泡滞留预测模型。研究成果不但可为多相流泵、核反应堆冷却剂主循环泵等叶轮机械优化设计和安全运行提供理论支撑，还有助于促进流体机械与多相流热物理间的学科交叉融合。

针对叶轮流道内的气泡滞留的动力学过程和机理及对泵性能的影响，开展了叶轮流道内气泡形态变化与运动规律、气泡滞留的动力学机理、动力学条件与模型三方面的研究。获得了离心泵叶轮内气液两相分布特性，绘制了相应的流型图，揭示了入口参数对叶轮内流型的影响规律；查清了四种流型下气泡动力学行为，揭示了气泡形态变化和动力学过程对气液相分布的影响规律；建立了基于CFD-PBM耦合模型的离心泵气液两相流数值模拟方法，与传统数值方法相比，能够更加有效的模拟气泡在离心泵内的聚并、破碎、分离等动力学行为，进而准确预测泵的“喘振”特性；获得了泡状流入口条件下离心泵气液两相外特性变化规律，揭示了气液两相流动特性及入口参数与泵性能变化的关联机制；阐明了离心泵扬程和效率等外特性的变化规律与泵内截面含气率及气泡尺寸分布的关联，对比了典型的截面含气率和气泡尺寸预测模型的准确性。项目研究结果可为多相泵的设计和安全运行提供理论支撑。以第一作者或通讯作者发表SCI检索论文5篇，EI检索论文7篇，国际国内会议论文报告共6篇；授权发明专利2项，实用新型专利2项，公示发明专利3项；培养硕士毕业生2名，在读博士生1名，在读硕士生2名；项目负责人贺登辉于2019年入选“西安理工大学优秀青年教师”培养计划，并于2020年12月晋升副教授。

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