The Influence Of Pump Impeller Diameter On The Hydraulic Performance Of Low Lift Vertical Flow Pump System

Pump stations of The East-Route Project of South-to-North Water Transfer have three characteristics: low head, large discharge and long operational time. Based on the characteristics, how to select pump system type reasonably to increase the efficiency of the pump system is an extremely important work for the project construction.Axial flow pump system, as a mature type, has been applied widely by hundreds of large pumping stations. Compared to other types of pump system, it has advantages of more steady-operation, higher reliability, more convenient installation and reparation, lower investment and maintenance cost. Furthermore, it is much more experienced in design, manufacture, operation and management. In order to make this mature type of pump system be applied more perfectly, it is necessary to break down the traditional opinion on the pump nD value and to study on hydraulic performance of axial flow pump system deeply and systematically.Based on primary dimension and water level combination of a certain large low-head pumping station, the numerical computations of 3D turbulent flow for the inlet and outlet conduits, which are matched with different pump impeller diameters, are completed respectively in this paper by the help of CFD theory and technology. According to the numerical computation results, the interior flow patterns are analyzed and the influence of different impeller diameter on the hydraulic loss of inlet and outlet conduit are quantitatively compared.The numerical computation of 3D turbulent flow for the model pump section is completed by the help of CFD theory and technology. The comparison between numerical computation and model test results indicates that it is feasible and has a certain accurate to simulate interior flow pattern in pump section and forecast the performance of pump section by the help of numerical computation. And the computation is also a necessary step for the numerical computation of interior 3D turbulent flow in a vertical axial pump system.The numerical computations of 3D turbulent flow for the pump systems with different diameter are completed by the help of CFD theory and technology, the flow pattern and hydraulic loss of both inlet and outlet conduit of the pump system are compared with the corresponding results, obtained by separate numerical computations for inlet and outlet conduits respectively. The results make it clear that the two results are consistent with each other.In order to verify the results of numerical computations, model tests for inlet and outlet conduits matched with different impeller diameters are completed to compare the difference between the numerical and test results on the flow pattern and hydraulic loss. It indicates that the two results are consistent with each other.It is beneficial to the selection of hydraulic model and improvement of cavitation performance for the low-head pump system to reduce pump nD value. The research in paper also indicates that:(1) The hydraulic loss of inlet and outlet conduit will be significantly reduced with the increasing of pump impeller diameter(inverse ratio to the 4 power of impeller diameter ).(2) The efficiency of a pump system will be remarkably increased by increasing pump impeller diameter appropriately, and the lower the head, the more notable the influence of pump impeller diameter.(3) Vertical axial flow pump system with appropriately increased impeller diameter could be acceptable as one of considerable scheme for low head pump system.