Fatigue Performance Investigation of Centrifugal Water Pump Shaft.

Abstract

Pump is a mechanical device that applies energy to move liquids from one place to another at increased pressure, flow rate and to an elevated height. The pumps can be divided into two general categories, namely dynamic pumps and displacement pumps. This study deals with centrifugal pump shaft which is one of dynamic pump type. Centrifugal pumps are widely used for irrigation, water supply plants, and steam power plants. From one of centrifugal water pump components, shaft is the rotary component used to support rotating components or to transmit power from motor to the ro tating components like impeller of the pump. Shafts may be subjected to a variety of loads such as tension, torsion, compression bending or a combination of these. For given geometries of impeller and volute, the global mechanical load acting on the shaft can be defined as the sum of the elementary loads including: axial load, radial load and bending moment and torsional load. The shaft of the rotor experiences both cyclic flexural load and torsional load during the pumping operation. The objective of the study is to investigate the fatigue performance of centrifugal water pump shaft under varying load conditions. In order to achieve the objective of the study, numerical and analytical static structural analysis of three stage centrifugal pump shaft was performed. Analytical and numerical result of static structural analysis of the shaft were in good agreement. In order to investigate fatigue performance of the shaft under varying load conditions, CFD analysis of three stage centrifugal water pump was carried out using ANSYS 19.0 CFX to get the pressure distribution of the impeller at different flow rate from 0.6Qd to 1.4Qd flow rates. For the fatigue analysis of the shaft one way Fluid Structural Interaction (FSI) analysis of three different materials was performed. Dynamic analysis of centrifugal pump shaft was also carried out by using the ANSYS 19.0 software to determine the mode shapes and natural frequencies of the shaft to investigate resonance conditions of the rotor shaft. In addition FSI stress analysis of impeller were also conducted for three different materials of impeller under different flow rates. The finding of the study shows that the fluid pressure on the impeller has great impact on the shaft causing high stress and deformation. The result of the study also reveals that the shaft of the pump experiences high stress at off-design operating conditions of the pump. Dynamic analysis of the pump shaft shows the pump is free of resonance condition and the critical speed of the shaft is greater than the operating speed of the pump