多级螺旋轴流式多相泵叶轮内气液两相流型及动静叶栅耦合机理研究

The helico-axial multiphase pump,which has the advantages of compact structure, have the capacity to pump more gas-liquid mixture fluids than the positive displacement technologies, represents the domianting development direction of offshore and subsea applications. However, gas liquid phase separation, which results in pressure differential and pump efficient declining, is apt to occur in the impeller of helico-axial multiphase pump due to the centrifugal force during impeller rotating. In order to resolve this question, some theoretical investigations will be carried out in this project. First of all, the visualization experiment on the basis of high-speed photography will be done to explore the gas liquid phase separation features in the helico-aixal impeller in the suction conditions of different gas void fraction (GVF). The purpose of the experiment is the uncover the position, scale and development regularity of gas liquid phase separation in the impeller. Furthermore, the calculating method of gas bubble average diameter and interfacial momentum transfer models under differential GVF will be discussed so as to improve the reliability of numerical simulation on the flow field of multiphase pump based on the result of visualization experiment. Finally, the validated numerical simulation method will be used to simulate the inner flow field of multiphase pump. On account of the result of numerical simulation, some desired conclusions will be uncovered are as followed: the relationships between the extent of gas liquid separation and suction conditions (such as, GVF, liquid viscosity and suction pressure) and geometric parameters of pump impeller (for instance, number of blade, impeller outlet blade angle, change rule of airfoil shape and hub angle of inclination), the flow rules of gas liquid two phase in the pump defuser, the effect of defuser geometric parameters on the gas liquid mixed ability of defuser as well. At the same time, the coupling between impeller and diffuser will be discussed in the project be means of CFD. The research outputs of this project have higher academic value with regard to develope the hydraulic design theory of helico-axial multiphase pump.

螺旋轴流式多相泵结构紧凑、排量大、可输送高含气流体，是深海油气混输设备的理想选择。本项目针对该泵叶轮内易发生气液分离，形成气囊，造成泵性能异常等问题，拟采用高速摄影、CFD与理论分析方法，研究多因素作用下多级叶轮内的流型特征、气囊产生机理及动静叶栅的耦合机理。首先以一台三级螺旋轴流式多相泵叶轮为研究对象，采用LED背景光源高速摄影技术研究不同工况下黏性气液混合物在叶轮内的两相流型与非定常特性，探索影响流型的介质与操作参数，明确多级叶轮内气囊的位置、规模与发展规律，及其对叶轮性能、压力脉动的影响程度；在实验的基础上，采用大涡模拟方法模拟多相泵内流场，揭示相态分离及气囊产生的机理；最后分析不同叶轮/导叶进出口角、轴向间距匹配关系下上游叶栅尾迹对下游叶栅内两相流场的影响，阐明动静叶栅耦合机制。研究成果推动深入认识螺旋轴流式多相泵叶轮内气液两相流动规律，为完善叶轮水力设计方法奠定理论基础。

螺旋轴流式多相泵叶轮采用大包角设计思路，结构紧凑、排量大、可输送高含气流体，是深海油气混输设备的理想选择。项目针对该类型泵叶轮运转过程中易发生气液分离，形成气囊，造成泵性能异常等问题，以一台自主研发的三级螺旋轴流式多相泵为对象，开展内流场可视化实验、流场数值模拟与理论分析，研究了不同介质参数与操作参数等多因素作用下多相泵入口段及三级叶轮内的流型特征，揭示了叶轮内部气囊产生的机理。研究发现：在不同来流含气率工况下，泵入口段（缓冲均化器出口）均表现为泡状流，验证了自主设计的缓冲器的可行性；入口段平均气泡直径随含气率的增加不断增大，随着转速增加而减小；及与实验数据，绘制了气泡平均直径随入口含气率及转速的变化规律曲线；随着入口含气率的逐渐增加，叶轮内气液两相流型主要表现为孤立的气泡流、泡状流、气囊状流和乳化状流四种类型，由于离心力和压力梯度的作用，气囊主要位于叶轮叶片压力面2/3弦长到出口附近，建立了两相流型与叶轮水力性能之间的关系，孤立的气泡流型下泵的增压变化较小，泡状流型下泵的增压下降较明显，气囊状流型下泵的增压急剧下降，而在乳化状流型下增压下降趋势较平缓；基于孤立气泡的受力分析，探索了叶轮内气泡的运动轨迹，结合可视化实验和流场数值模拟，揭示了多相泵叶轮内气囊的形成机理；在动静耦合研究方面，同一级内动静结合处监测点的压力脉动峰峰值与功率谱密度均较小，相邻两级之间动静结合处监测点的压力脉动峰峰值与功率谱密度最大，说明相邻两级之间动静干涉引起的压力脉动最大，有必要对导叶结构、叶轮进口结构或相邻两级之间的轴向间距进行优化，以便降低这里的压力脉动；在同一转速工况下，压力脉动系数随进口含气率的增加整体上呈现先下降后上升的趋势，说明含气率的增加在一定程度上可以减缓压力脉动的程度，过高的含气率则增强压力脉动；将三元水力设计方法与涡动力学诊断、遗传算法相结合，提出了多相泵叶轮优化设计方法，采用边界涡量流的均匀分布度作为适应度值的评价方法，采用遗传算法不断迭代实现多相泵叶轮的不断优化，优化后提高了多相泵叶轮的增压，拓宽了高效区的范围。项目研究成果可以推动深入认识该类型多相泵叶轮内气液两相流动规律，为完善该类型泵叶轮逐级水力设计方法提供理论参考。