基于计算流体力学的串列轴流泵空化性能分析

Analysis of Cavitation Performances of an Axial Flow Tandem Pump Based on Computational Fluid Dynamics

对一串列轴流泵内部空化流场进行计算,研究设计流量下串列泵内部空化发展过程,分析串列泵的空化性能。湍流模型采用一种RANS/LES的混合模式FBM模型,通过二次开发引入到计算软件;采用Zwart空化模型处理相间质量传输过程。基于一普通轴流泵的试验空化特性数据对上述计算方法进行验证,结果表明上述计算方法可以较好地预测轴流泵的空化特性。研究结果表明,在设计流量下,串列泵内部空化发展可以分为四个阶段:空化初生阶段、首级叶轮空化发展阶段、次级叶轮空化发展阶段和空化充分发展阶段。在首级叶轮空化发展阶段和次级叶轮空化发展过程中,串列泵的能量特性存在一个过渡阶段。在该过渡阶段,串列泵整体外特性仍具有较高水平,这是由于首级叶轮外特性下降的同时次级叶轮外特性稍有上升。

Computations of the cavitating flows in an axial flow tandem pump are conducted to analyze the cavitation performances.FBM turbulence model is adopted to close governing equations,which combines RANS and LES together.Turbulent model is introduced to the CFX commercial code using re-developing method.Zwart cavitation model is used to process the mass transfer in the cavitation process.Cavitating flows in a conventional axil flow pump are calculated to get the model validation and predicted cavitation performance compared well with experimental data.The results of tandem pump demonstrate that with the decrease of available net positive suction head（NPSHa）,the cavitation development in tandem pump can be divided into four stages：Inception cavitation,developing cavitation in front impeller,developing cavitation in back impeller and developed cavitation in the whole pump.During the second and third stages,transitional energy performances of the tandem pump can be observed.In this transitional process,no obvious decrease for the head and efficiency of the tandem pump can be observed.It＇s because the energy performance of the back impeller increases slightly while that of the front impeller decreases.