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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 the high number of revolutions. In order to minimize the impeller weight the requirements to study and develop the CP with semi-open impeller appear. The present paper is devoted to revealing 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 L/s). These CP performance parameters include the pump head, efficiency, slip factor, blade loads and the internal flow structure. The numerical simulation has been compared with own experimental results and a published empirical formula 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 has a great regression effect on the centrifugal pump 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.

The effect of impeller blades shape modification on the centrifugal pump performance has been investigated numerically. Impeller blades’ shape have been modified by new technique called “bladelet”. This technique has been called the “bladelet” after the name of the aeroplane winglet because of the great similarity between them in shape and function. The shapes of the blade trailing edge greatly affect the performance of the turbomachines. So, the purpose of the blade tilting (bladelet) is to decrease the recirculating flow at the pump trailing edge due to the high pressure difference and enhance the hydraulic performance of the centrifugal pump. The bladelet technique has two main geometrical parameters: radial position RBL and bladelet inclination angle θBL. 3-D validated numerical simulation model has been carried out using commercial software, ANSYS® CFX, to study the effect of the bladelet technique and its different parameters on the pump performance at different flow rates. In this study nine cases with different bladelet parameters have been numerically simulated in order to check its effect on the centrifugal pump performance. These nine cases have been chosen by considering the geometrical constrain of the bladelet parameters. The results of these nine cases have been compared with the basic impeller (the same impeller but without bladelet) at the same operating condition in order to discuss the effect of the bladelet parameters variation on the centrifugal pump performance. It was found that the use of the bladelet technique decrease the pressure difference between the pressure and the suction side at the blade trailing edge. This decrease in pressure difference at the blade trailing edge decreases the flow recirculation at the impeller outlet from pressure side to suction side. Also, bladelet technique improves the hydraulic efficiency at the part-load operating zone. In addition, the bladelet has a regression effect on the pump head for some cases with high inclination angle and low radial position. However, the bladelet technique increases the impeller blades’ overlap.

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 centrifugal pump performance depends to great extent upon the flow pattern in the impeller passages. When the pump operates at small flow rates, the problem of circulation due to vortex formation in the impeller passages is found. A new method is introduced to control and reduce the size of generated vortices in the impeller passages. Slots are opened in the impeller vanes to allow fluid to flow from the pressure side to the suction side of the vane. The bleeding fluid could reduce the size of the vortices. It is found to depend mainly upon the length and the position of the slot. In the present work, the flow field is solved in the radial impeller passages using the stream function and the primitive variable approaches, to solve the flow equations. The flow pattern is used to compare the vortex size and the pump head for both cases with and without slotted impeller vanes at different slot sizes and at different positions. The slot position that produces the highest pump head, the slot length has been changed until the smallest vortex size is achieved. The numerical solution is introduced in a code program form, which is written in the Microsoft Visual C++ 6 language. Finally the optimum position and length of the slot is obtained at Rs/R2 = 0.4981, and with L /(R2-R1)= 0.2291. The model has been validated by comparison to a published experimental result of the same pump (for the same research program).