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Centrifugal pumps (CP) are probably among the most often used machinery in industrial facilities as well as in common practice. Compared to other types of rotating pumps, CP yield higher efficiency. In aerospace application reducing the weight of the CP impeller has the advantage of reducing mechanical stresses and enable using the CP at high number of revolution. In order to minimize the impeller weight the requirements to study and develop the CP with semi-open impeller appears. Using this type of impeller results in clearance between the impeller blades and the casing which degrade the centrifugal pump performance. The impact of this side clearance has not been deeply investigated in open literature. The present paper is devoted to reveal more details about the impact of CP side clearance on its performance. This is done by numerically investigating the influence of the variation of the CP side clearance width (0:0.2 impeller width) on the CP performance parameters at different flow rates (0:5 Liter/s). These CP performance parameters include the pump head, efficiency, slip factor, blades loads and the internal flow structure. 3-D steady numerical simulation has been carried out using commercial software, ANSYS® CFX. The computational domain consists of four zones: inlet, side gab, impeller and volute with outlet. They are defined by means of the multi-reference frame technique. The impeller is situated in the rotating reference frame, while the inlet, side gab and outlet zones are in the fixed reference frame, and they are related to each other through the “frozen rotor” interface. The meshes of four computational domains are generated separately after performing mesh sensitivity analysis. The boundary conditions are set as total pressure at inlet and the mass flow at outlet. A no-slip condition is imposed at the wall boundary defined at the blade and casing. A turbulent, incompressible flow solver has been adapted using SST k–ω turbulent model. The numerical simulation has been compared with own experimental results and a published empirical formulas to verify the numerical solution. The CFD results show an acceptable agreement with the results of the experimental work and the empirical formulas. It has been shown that the impeller side clearance have a great regression effect on the centrifugal pump performance. An explanation to the performance regression has been proposed based on the flow field feature. Performance regression could be attributed to the drop in the pressure difference between the impeller inlet and outlet. And the redistribution of the velocity inside the impeller channel and the side clearance.

The effect of impeller backward blades with slot on the centrifugal pump performance has been investigated numerically. Impeller blades have been modified with different geometrical parameters of slot such as: slot radial position ሺܴ ௦ ሻ, slot height ሺ݄ ௦ ሻ and slot inclination angle ሺߠ ௦ ሻ. 3-D numerical simulation has been carried out using commercial software, ANSYS® CFX, to study the effect on the pump performance at different flow rates. The numerical simulation has been compared with previously published experimental results to verify the numerical solution. In addition, the results have been compared with the impeller without slots for the same operating conditions. It has been shown that the slot parameters have a significant effect on the centrifugal impeller performance.

The effect of impeller side clearance (the gap between the impeller face and the casing) on the centrifugal pump performance has been investigated numerically through monitoring the change of the pump head and efficiency at different flowrate. 3-D numerical simulation has been carried out using commercial software, ANSYS® CFX. The numerical simulation has been compared with experimental results to verify the numerical solution. In addition, the results have been compared with the closed impeller with front shroud at the same operating conditions It has been shown that the impeller side clearance have a great regression effect on the centrifugal pump performance. This regression on performance could be attributed to the drop in the pressure difference between the impeller inlet and outlet. And the secondary flow across the blade tip which impedes the core flow.

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