NUMERICAL STUDY ON FLOW FIELD INSIDE A CENTRIFUGAL IMPELLER PASSAGE

Abstract

The aim of this thesis work is to numerically simulate the three dimensional flow in a centrifugal slurry pump. A centrifugal slurry pump having an impeller of six twisted blades surrounded by volute casing has been selected for numerical simulation work. A commercial three-dimensional Navier-Stokes equation solver code called `FLUENT', with standard k-s two equation turbulence model is used to simulate the flow inside the pump at design and off-design conditions. The steady-moving reference frame (MRF) model is used for simulation of flow inside the rotating impeller. Finite-Volume method and unstructured grid system are used for solution of the discretized governing equations. The numerical results of performance characteristics have been compared with the manufacturer's data and also with the predictions by loss analysis procedure proposed by Gandhi (1998). Comparison of results obtained by various turbulence models has shown that the standard k-s model is more appropriate for simulation of flow in turbomachinery. The present work shows that the performance characteristic of pump can be numerically predicted in 3 days time periods at 1.8 GHz Pentium 4 processor with 512 MB RAM computer. The time period may be further reduced by using of high speed CPU. The unequal flow distribution in vane channels has been found at best efficiency point (BEP) and higher than BEP flow rate. The internal circulation of flow at outlet of vane has been observed at low delivery flow rates. Separation zone near the volute tongue and low pressure zone in one of the vane channels have been observed at flow rate higher than BEP. Comparison of computational results for various flow rates has showed good agreement with manufacturer's data. However loss analysis procedure shown much difference at very low (0.3 m3/min) and very high (.6 m3/min) flow rates