3-D CFD analysis of flow in a mixed-flow pump diffuser

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Zhao, Yi
Mechanical engineering
thesis / dissertation description
The primary goal of the project was to gain insight into the flow pattern in a mixed flow pump diffuser by using FLUENT CFD code and k-e turbulence model, and improve the design of a diffuser for higher pump efficiency. The diffuser chosen in this thesis is used in a mixed flow multi-stage pump which collects the nearly radial flow (water) at impeller discharge and converts it to a nearly axial flow at the inlet of the following pump stage. A three-dimensional computational model was developed for three different diffuser designs labeled as Diffuser A, Diffuser B and Diffuser C. CFD results indicated that Diffuser C had better pressure recovery characteristics than both Diffuser A and Diffuser B. These results were confirmed by comparing with the experimental data for these diffusers provided by the pump manufacturer. The major conclusion resulting from the flow pattern study for Diffuser A, B and C is that the exit angle of the mean flow near the hub side of the diffuser has a strong effect on the diffuser performance. The greater the flow exit angle, the higher the degree of secondary flow formation which tends to reduce static pressure recovery. Based on that finding, several different diffuser geometries were modeled in an effort to reduce the exit flow angle. It can be concluded from this work that FLUENT CFD code can be used to model internal subsonic flows with a high degree of confidence. There was good correlation between model results and manufacturer's test data.