Blade Design Effects on the Performanceof a Centrifugal Pump Impeller

John S. Anagnostopoulos

Abstract This work performs numerical simulations of the flow in a centrifugalpump impeller in order to investigate the influence of blades parametric design onthe impeller performance and efficiency for a wide operation range. The combineduse of orthogonal unstructured grids and of a specific cut cell boundary methodenhances the results accuracy and provides a fully automated computational envi-ronment suitable for numerical design optimization. The results showed the poten-tial of remarkable increase in efficiency by optimizing the impeller design.

1 Numerical Methodology

The flow simulation in the impeller (Fig. 1a) is performed by solving the RANSequations with the finite volume method, while turbulence closure is obtained by thestandard k- model. Key feature of the present approach is the use of unstructuredorthogonal grids that can be constructed in a fast and fully automated way. Theaccuracy of the results at the flow boundaries is enhanced by the use of a conser-vative cut-cell sharp-interface approach [3], along with an adaptive grid refinementtechnique [1], applied here at the blades region (Fig. 1b).

The impeller is parameterized using a reduced number of geometric variables,while Bezier polynomials are used for the blades design (Fig. 1c). The hydraulicefficiency of the impeller equals to the net energy (head) added to the fluid, dividedby the energy given at the shaft. The net fluid head is obtained by energy balancingat the inlet and outlet, whereas the calculation of torque developed on the bladesis computed from the resulting pressure field. The region and the magnitude of theminimum pressure are also monitored to assess the suction efficiency of the impellerin respect to cavitation.

J.S. Anagnostopoulos (B)School of Mechanical Engineering, National Technical University of Athens, Athens, Greecee-mail: anagno@fluid.mech.ntua.gr

A. Kuzmin (ed.), Computational Fluid Dynamics 2010,DOI 10.1007/978-3-642-17884-9_109, C Springer-Verlag Berlin Heidelberg 2011

859

860 J.S. Anagnostopoulos

(a) (b) (c)

P1P2 P3

P4P5

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Fig. 1 Sketch of the centrifugal pump impeller (a); computational domain and the adaptivelyrefined grid (b); blade shape parameterization (c)

2 Application and Results

The numerical method is applied to study the flow development in the impellerfor various designs and operation conditions (nominal and off-design). The resultscan provide detailed pictures of the flow, facilitating the analysis of the impellerperformance (Fig. 2). The algorithm is then used to conduct various parametricstudies of the effect of blades geometry on the impeller performance characteristics.Blade length and chord angle, number of blades, and solidity factor are among thetested design variables, whereas inlet and outlet blade angles and height are fixed tooptimum values from previous studies [2].

Figure 3 shows the resulting impeller performance curves for different bladelength. This parameter affects both the maximum efficiency and the BEF point loca-tion (Fig. 3a). On the other hand, the minimum pressure data in Fig. 3b represent

(d) (a) (b) (c)

Fig. 2 Computed pressure field (a, c) and velocity field (b, d) for: off-design (low load) conditions(a, b), and near BEF operation (c, d)

Fig. 3 Effects of blades length: (a) Hydraulic efficiency curves; (b) Minimum pressure values inthe impeller

Blade Design Effects on the Performance of a Centrifugal Pump Impeller 861

the cavitation characteristics of the corresponding impellers, which may be consid-erably different in some operation regions.

From the above and the rest parametric studies it is concluded that a remarkableincrease in hydraulic efficiency of the impeller can be achieved by adjusting thevalue of certain design parameters, hence there is a potentiality to improve furtherthe hydrodynamic performance of centrifugal pumps. The fully automated param-eterization and grid construction techniques used in this work are very suitable forsuch numerical design optimization.

References

1. Anagnostopoulos, J.: Discretization of transport equations on 2D Cartesian unstructuredgrids using higher-order schemes for the convection terms. Int. J. Num. Meth. Fluids 42(3),297321 (2003)

2. Anagnostopoulos, J.: CFD analysis and design effects in a radial pump impeller. WSEASTrans. Fluid Mech 1(7):763770 (2006)

3. Anagnostopoulos, J.: A Cartesian grid method for the simulation of flows in complexgeometries. Proceedings of the 3rd International Conference ADMOS 2007, Gteborg, Swe-den (2007)

Blade Design Effects on the Performance of a Centrifugal PumpImpellerJohn S. Anagnostopoulos1 Numerical Methodology2 Application and ResultsReferences

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