Influence of an Inlet Rotating Axial Device on the Cavitation Processes in a Low Specific Speed Centrifugal Pump

Abstract

The paper is devoted to the analysis of the cavitation processes in the flow section of the low specific speed centrifugal pump. A new conception of double-entry hermetic pump leads to the application of special shaped inlet device, which is a part of an electrical motor rotating element. Four flow geometrical models of the axial inlet device were taken into consideration. The first model, treated as referential and basic, has a cylindrical shape with small diffuser and a cone in front on the impeller. Other three models consist of the motionless cone, which was part of the housing, straight pipe, and diffuser section rotating analogously to the impeller and a spherical fairing. The research was conducted using physical experiments and numerical simulations of the workflow in the ANSYS CFX software environment. The analysis of the results shows that the pump with the basic model of the inlet device has NPSH 3 % above the average values. The comparison between CFD and experiment of the cavitation curves shape showed its similarity but determined by means of the physical experiment have higher values. Cavitation in the impeller starts earlier than in the axial inlet device. The zones of the cavitation in the axial inlet device are located after the cone, at the beginning of the diffuser section and near the fairing at the outlet of the diffuser section. The cavitation zone, which is located after the cone, is separated from the walls of the axial inlet device. The value of the NPSH 3 % increases, when the diameter of the axial inlet device decreases, as the result of the raise of head loses in the inlet structure.