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Influence of Blade Wrap Angle on Centrifugal Pump Performance by Numerical and Experimental Study

The pressure distributions in centrifugal pumps are shown in Fig. 7, Fig. 8 and Fig. 9. The pressure gradually increases from the impeller inlet to the volute outlet, with the minimum value at the leading edge of the suction
surface on the blades. The pressure distribution in each flow passage is not periodic due to the asymmetric geometry of the volute and the interaction between the impeller and the volute. The detailed scrutiny into pumps A, B and C indicates that the pressure distributions are
different at small flow rate. It is more uniform at the volute inlet of pump C than that of pumps A and B. For the design and large flow rates, the pressure increase in centrifugal pump C is more regular than that of pumps A and B.

3.5 Performance prediction
To further analyze the hydraulic performance of centrifugal pumps, their heads and efficiencies are also computed. The head of centrifugal pump is defined as the head difference between the outlet and inlet of the pump.
The head data is the flow-rate weighted value in terms of the computational results that calculated as follows:

The heads and efficiencies of pumps A, B and C are nearly the same at the low flow rate. At the design and large flow rates, the head and the efficiency of pump C are greater than the pumps A and B by maximum values of 3.6% in head and 1.6% in efficiency respectively. The pump characteristics show that the blade wrap angle has an effective influence on the centrifugal pump performance, which is in consistence with the analysis of the internal flow fields.
4 Experiment
To verify the numerical result and analysis, the performance test apparatus for the centrifugal pumps is designed and built, as shown in Fig. 10. It consists of a water supply section (parts 4–5), a pump section (parts 1–3)
and an exhaust section (parts 6–8).

Fig. 11 shows the performance curves of centrifugal pump C, where the square symbol denotes the head H, triangle symbol denotes the efficiency η, and circle symbol the shaft power P, all of which vary with flow rate Q. The results show that the highest efficiency of centrifugal pump C is 77.4% at flow rate of 225.81 m3/h and the head of 30.52 m. The centrifugal pump C has a wide range of high efficiency around the design point and a wide stable operation. The good quantitative agreement between the experimental and numerical results is shown in Fig. 11 which verifies the accuracy of the numerical simulation.

5 Conclusions
(1) Three centrifugal pump impellers with blade wrap angles of 100°, 110°, 120° are designed using the direct and inverse iteration design method, which calculates the meridional velocity by iterating the two stream surfaces and draws the blade shape by controlling the blade wrap angle.
(2) The internal flow fields in three centrifugal pumps with different blade wrap angles are numerically simulated.Compared with pumps A and B with blade wrap angles of 100° and 110°, the pump C with blade wrap angle of 120°has a better flow characteristic on both velocity and pressure distributions. The head and efficiency of pump C are higher than those of pumps A and B by maximum values of 3.6% in head and 1.6% in efficiency respectively.
(3) The experimental results show that the pump with the largest wrap angle has wide area for high efficiency and stable operation. Both numerical and experimental results verify the design method and numerical analysis, and
demonstrate that the blade wrap angle is a very important parameter in pump designing and has a great influence on pump performance.

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