设计工况下离心泵作液力透平内部流动耗散特性研究

Analysis of the Flow Loss Characteristics of the Centrifugal Pump as Turbine(PAT)under the Design Operation Conditions

离心泵反转作液力透平是一种能量回收装置,但缺点是即使在设计工况下的效率也相对较低。为揭示液力透平的流动耗散特性,文章首先通过流体动能方程构建了涡量与流动耗散之间的关系。随后,基于拟涡能耗散理论对设计工况下的流动耗散进行了定量计算。最后,对主要损失部件内的拟涡能耗散分布特性与局部主要流动特征进行了关联分析,进而揭示了透平内部流动耗散的发生位置和产生原因。结果表明:拟涡能耗散评估方法能够较为准确地计算透平的流动损失,设计工况下各部件损失占比大到小排列分别为:叶轮、蜗壳、腔体、出口段和进口段。叶轮内局部拟涡能耗散主要发生在吸力面的前缘下游及叶片尾缘附近,叶片前缘冲击、回流、旋涡等不稳定流动是导致叶轮内局部拟涡能耗散的主要原因。蜗壳的拟涡能耗散主要由出口回流、隔舌前缘及壁面处的附着旋涡粘性耗散引起,腔体的拟涡能耗散主要由前腔间隙射流所引起的旋涡耗散及壁面旋涡粘性耗散组成。出口管的流动耗散特性主要受叶轮出流条件的影响,前腔间隙射流会对出口管内的主流产生冲击并引起局部水力耗散。研究结果可为高性能液力透平的设计提供参考。

The centrifugal pump as turbine(PAT)is an energy recovery equipment with relatively low efficiency even under its design operation condition.To reveal the flow loss characteristics of PATs,we firstly obtained the relationship between the vortexes and the flow dissipation from the momentum equation of fluid.Subsequently,based on the enstrophy dissipation theory,the flow loss of the PAT under the design operation condition was quantitatively calculated.Finally,the correlation analysis between the enstrophy dissipation distribution characteristics and the main local flow features was carried out in the main flow domains of PAT,and further revealed the location and cause of flow dissipation in the PATs.The results show that the flow loss in the PAT can be calculated comparatively accurately using the enstrophy dissipation method,and the flow loss proportion in the PATs under the design operation condition from large to small was arranged as follows:impeller,volute,chamber,outlet section and inlet section.The local enstrophy dissipation rate in the impeller under the design operation condition was mainly generated at the downstream of the suction side front edge and near the blade trailing edge.Unsteady flow such as blade leading edge shock,backflow,flow separation and vortices are the main causes of local flow loss within the impeller.The volute enstrophy is mainly caused by the backflow on the outlet,bound vortex near the leading edge of the volute tongue and walls.The chamber enstrophy is generated from the leakage flow inner the front chamber wear ring and bound vortex near the walls.The outlet condition of the impeller determines the enstrophy of the outlet pipe,and the leakage flow from the front chamber will shock the main flow of the outlet pipe and cause local flow dissipation.The results can give references to the design of excellent performance PATs.