Numerical Simulation for Design Improvement in Diffuser of Multistage Centrifugal Pump

Abstract

AbstractA multistage centrifugal pump is generally a type of common centrifugal pump which contains number of impellers in series on single shaft. A regular centrifugal pump consists of volute casing, whilst in multistage pump, it has diffuser whose function is same as that of volute casing. To guide the flow to next succeeding impeller, a return passage channel is used. The efficiency of a multistage centrifugal pump depends upon the number of impeller blades, blade profile, diffuser profile, rotational speed of the impeller. In this paper, performance analysis of multistage centrifugal pump is carried out by increasing the vaned diffuser outlet heights with different rotational speeds to investigate their effect on the head and efficiency. A model is prepared in Ansys design modular, and each domain, i.e. impeller, diffuser, and return passage is made separately and then imported in ICEM CFD where meshing of each domain is done. The model is imported to CFX—PRE where boundary condition at inlet and outlet is applied, and domains are interfaced with each other. The flow simulation is carried out under k–ε turbulence model. It is observed that with the increase of rotational speed, the head developed by the pump increases up to 20% increment in vaned diffuser outlet height, and it is then decreases because of increase in spiral flow (vortex formation) in the diffuser. It is also found that the pump gives the best head of 117.37 m at a 20% increment in existing height of vaned diffuser at 1900 rpm, but there is decrease of the efficiency is about 1.82%.KeywordsHydraulic machineMultistage centrifugal pumpVaned diffuserComputational fluid dynamics (CFD)Standard k–ε turbulent equation