Effects of non-uniform elbow inflow on the unsteady flow and energy development characteristics of a centrifugal pump

Abstract

A non-uniform inflow caused by an elbow structure is one of the main reasons for the low energy transformation efficiency of a centrifugal pump. Prototype experiments for the centrifugal pump are used to analyze the transformation rule of pump energy characteristics under the uniform inflow and non-uniform elbow inflow. The non-uniform elbow inflow increases the hydraulic losses in the centrifugal pump to reduce the pump head and operation efficiency. The pump efficiency decreases by 8% under the design flow condition. The large eddy simulation with a shear-modified eddy viscosity model is applied to simulating flow excitation characteristics and energy development features. The non-uniform inflow increases the impact loss at an impeller inlet and produces unsteady flow excitation in the impeller passage. The elbow inflow affects the pressure fluctuation frequency, and the main frequency is twice the blade-passing frequency (250 Hz). The high entropy production regions are mainly concentrated at the suction surface of the blade and the interface of impeller and volute, coinciding with the unsteady flow areas in the pump. The asymmetrical entropy yield distribution in the elbow inflow pump is intensified because of the increase in the flow loss caused by the non-uniform inflow.