气液两相流下离心泵内部流动机理及其流动诱导特性研究

Pumping system involving gas-liquid two-phase flow can be found widely in the nuclear powers, chemistry, petroleum and related high-end technology. With the increase of gas void fraction, the performance of centrifugal pump could deteriorate gradually till zero flow, which seriously affects the system security and operation stability. Due to the complex structure of centrifugal pump, the flow characteristics and the performance deterioration mechanism under gas-liquid two-phase flow condition has not yet been revealed, and therefore, it is still a hot spot in the research field of hydraulic machinery at present. In this project, the combined method of theoretical analysis, numerical simulation and experimental study will be used to explore the internal flow mechanism and flow induced characteristics of the centrifugal pump under gas-liquid two-phase flow condition. Firstly, the gas-liquid two-phase flow test rig for centrifugal pump will be built to realize integrated synchronous measurement for pump performance, inner flow visualization and flow-induced time-frequency characteristics. Secondly, the existing turbulence and multiphase flow model will be improved to establish the numerical method of gas-liquid two-phase flow in centrifugal pump. Then, based on the obtained numerical simulation and experimental results, the flow mechanism and flow induced characteristic of centrifugal pump under gas-liquid two-phase flow condition will be revealed to explain the performance deterioration under high gas void fraction, and the sensor-less flow monitoring technology will be developed. Finally, three prototype pump models with low, middle and high specific speed will be tested for validation, which can provide theoretical and practical basis for the reliable operation of high-end centrifugal pump system in China.

在核电、石化和油气开采等高端技术领域经常会碰到泵送气液两相流的现象，随含气率的增加，离心泵的性能逐渐恶化，直至断流，严重影响系统的安全稳定和运行。由于离心泵结构复杂，气液两相流下其内部流动特性和性能恶化机理至今仍未揭示，是水力机械领域的学术热点。本项目拟采用理论分析、数值模拟和实验研究相结合的方法，探求气液两相流下离心泵内部流动机理并掌握其流动诱导特性。首先搭建专用气液两相流实验台，实现可视化模型泵外特性、内部流动结构及其诱导时频域特性的一体化同步测量；其次对现有数值模型进行改进，构建离心泵气液两相流数值计算方法；然后基于数值模拟和实验结果，获得离心泵气液两相流下的内部流动规律及流动诱导特性，揭示高含气率下离心泵性能恶化机理，建立离心泵气液两相流无传感器流态监测方法；最后进行低、中、高三种比转数离心泵气液两相流条件下的真机测试和验证，为我国高端离心泵系统可靠运行提供理论基础和实践依据。

随含气率的增加，离心泵的性能逐渐恶化，直至断流，严重影响系统的安全稳定和运行。项目搭建了离心泵多场同步测试台，实现了模型泵外特性、内流可视化、以及压力脉动、定子电流、振动等的同步测量。基于该实验台测量入流含气条件下，高、中、低三种比转速离心泵的性能和流动诱导特性，研究发现叶轮出口圆周速度的影响泵输送最大含气率的重要因素，相同的u2下泵不同入流含气率下的性能相同，可输送的最大含气率由转速决定，转速越高，可输送的最大含气率越大。测试的中、高比转速离心泵在2900r/min泵设计流量工况，均可在含气率10%时运行，低比速离心泵入流含气率5%以后性能即急剧恶化。离心泵气液两相流条件下压力信号和振动信号均服从正态分布；当进口含气率超过5%时，发现低频区压力脉动幅值明显增大；振动信号的整体幅值会随着含气率的增大明显增大，尤其是在低频段区域，随着含气率逐渐增大，振动呈先减小后增大再减小的趋势，在进口含气率5%时振动最大，进口含气率超过5%后，低频区振动能量也会成为泵系统振动能量重要组成部分。分析比较了传统欧拉-欧拉气液两相流模型与Musig模型在计算入流含气工况下离心泵内部流场的优劣并开发一种考虑气泡直径变化的气液两相流粒子模型。通过与内流可视化实验结果对比，发现随着入流含气率的增加，叶轮和蜗壳流道内逐步出现均匀泡状流、聚合泡状流、气穴流和分离流等不同的气液两相流流型分布，不同流型的转化伴随着气泡的聚并和破碎，进而严重影响到流场内部能量的波动，导致泵内流场的不稳定性加剧和性能恶化，最终流道堵塞发生断流。项目还发展了基于定子电流信号分析的离心泵气液两相流态监测技术。项目研究可为高端离心泵系统可靠运行提供理论基础和实践依据。