空化对多相混输泵内流动特性的影响

Effect of Cavitation on Flow Characteristic of Multiphase Pump

为揭示螺旋轴流式多相混输泵的空化性能及不同空化阶段下多相混输泵性能的变化规律,基于标准κ-ε湍流模型和Rayleigh-Plesset空化模型,对螺旋轴流式多相混输泵空化性能进行数值模拟,分析不同空化阶段空泡的发展对流速和压力分布的影响,揭示空化现象造成泵扬程下降的主要原因。结果表明,在螺旋轴流式多相混输泵内,在空化初生阶段,空泡主要集中在叶片吸力面进口处,随着空化余量的减小,空泡沿叶片吸力面流线方向逐渐延伸,当空化余量为0.8m时,空泡同时出现在压力面和吸力面上;当空化发展到压力面时,易导致混输泵的做功能力急剧下降;空泡体积分数越大,空泡末端区域的压力梯度变化就越大,会造成边界层分离和回流现象,加速空化的发展;空化会干扰叶轮内部流体的流动,使得空化区域流体的流速变化较大,从而导致流动的稳定性变差。研究结果可为多相混输泵性能的改善提供参考。

In order to reveal the cavitation performance of multiphase pump and the evolution mechanism of the performance of multiphase pump under different cavitation stages,numerical simulation is performed on cavitation performance of multiphase pump by coupling the standardκ-εturbulence model with Rayleigh-Plesset cavitation model.The influence of development of bubbles on velocity and pressure distribution under different cavitation stages is studied,and the main reason for decrease of head caused by cavitation is revealed.The results show the vapor mainly concentrates at the suction side near leading edge in incipient stage of cavitation.With the decrease of net positive suction head(NPSH),the bubbles extend gradually along the streamlines of the suction side of blade.When the NPSH value is 0.8 m,the bubbles appear on the pressure side and suction side simultaneously.When cavitation develops to the pressure side,it will easily lead to a sharp decline of the pump lift.With the increase of volume fraction of bubbles,the greater pressure gradient at the rear of the bubbles region causes boundary layer separation and back-flow,and then accelerates the development of cavitation.The cavitation interferes the flow of the impeller,leading to the velocity of the fluid sharply varies in cavitation region,and the flow becomes unstable.The results can provide a reference for improving the performance of multiphase pumps.