Sig Turbomachinery / ERCOFTAC centrifugal pump with a vaned diffuser

1 The ERCOFTAC centrifugal pump with a vaned diffuser

Maryse Page, Hydro-Québec, Montréal, Canada

Hakan Nilsson, Chalmers University of Technology, Gothenburg, Sweden

1.1 Testcase description and experimental results

The testcase was presented by Combès [1] at a Turbomachinery Flow Prediction ERCOFTAC Workshop. The simplified model of the centrifugal pump has 7 impeller blades, 12 diffuser vanes and 6% vaneless radial gap. More information about the geometry and the operating conditions are described in the paper of Ubaldi, Zunino, Barigozzi and Cattenei [2]. The geometry is illustrated in Figure 1.

Figure 1: Impeller and vaned diffuser geometry (Image taken from Ubaldi, Zunino, Barigozzi and Cattanei [2])

The experimental data was provided by Ubaldi et al. [2][3][4]. The model operates in an open circuit with air directly discharged into the atmosphere from the radial diffuser. The pump operates at the nominal operating condition, at a constant rotational speed of 2000 rpm. (Reynolds number: 6.5x10^5, incompressible flow regime). Phase locked ensemble averaged velocity components have been measured with hot wire probes at the impeller outlet. The data includes the distribution of the ensemble averaged static pressure at the impeller front end, taken by means of miniature fast response transducers mounted at the stationary casing of the impeller. LDV measurements were also performed in the impeller and in the diffuser.

It is interesting to note that two-component LDV measurements of the vane unsteady boundary layer were recently published by Canepa, Cattanei, Ubaldi and Zunino [5]. Also, detailed flow measurements within the impeller and the vaneless diffuser have also been published [6]. It is the same impeller used in the measurements of the pump [2][3][4].

1.2 Published computational results

Computations have been performed by Bert, Combès and Kueny [7][8][9], Torbergsen and White [10], Sato and He [11][12][13], and Théroux et al [14][15]. A 2D model corresponding to a meridional plane with a radial inlet, and a 3D model were initially analyzed by Bert. His work showed that relevant information could be recovered from 2D simulations although the real flow has 3D features. Torbergsen also made computations with a 2D model. Sato and He performed a 3D simulation of a single impeller and two (2/14 instead of 2/12) diffuser blade passages, and a complete 3D model. Théroux analyzed two unsteady 2D models: complete (7 rotors/12 stators) and simplified (1 rotor/2 stators). The simplified 2D model yielded pressure fluctuations caused by rotor-stator interactions that were comparable to those of the complete 2D model.

Preliminary results have shown that OpenFOAM can produce similar results as other CFD codes for frozen rotor computations [16].

1.3 References

[1] Combès, J.F., "Test Case U3: Centrifugal Pump with a Vaned Diffuser", ERCOFTAC Seminar and Workshop on Turbomachinery Flow Prediction VII, Aussois, jan 4-7 , 1999.

[2] Ubaldi, M., Zunino, P., Barigozzi, G. and Cattanei, A., "An Experimental Investigation of Stator Induced Unsteadiness on Centrifugal Impeller Outflow", Journal of Turbomachinery, vol.118, 41-54, 1996.

[3] Ubaldi, M., Zunino, P., Barigozzi, G. and Cattanei, A., "LDV Investigation of the Rotor-Stator Aerodynamic Interaction in a Centrifugal Turbomachine", 8th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 1996.

[4] Ubaldi, M., Zunino, P. and Cattanei, A., "Etude expérimentale de l'écoulement instationnaire dans le diffuseur aubé d'une turbomachine centrifuge", La Houille Blanche, no 3/4, 31-37, 1998.

[5] Canepa, E., Cattenei, A., Ubaldi, M. and Zunino, P., "Wake-boundary layer interaction on the vaned diffuser of a centrifugal state", Proc. IMechE, vol. 219, Part A: J. Power and Energy, 401-411, 2005.

[6] Ubaldi, M., Zunino, P. and Ghiglione, A., "Detailed flow measurements within the impeller and the vaneless diffuser of a centrifugal turbomachine", Exp. Thermal and Fluid Sci., vol.17, 147-155, 1998.

[7] Bert, P.F., "Modélisation des écoulements instationnaires dans les turbomachines par une méthode éléments finis", Doctoral Thesis, Institut National Polytechnique de Grenoble, 1996.

[8] Bert, P.F., Combès, J.F. and Kueny, J.L., "Unsteady Flow Calculation in a Centrifugal Pump Using a Finite Element Method", Proceedings of the XVIII IAHR Symposium on Hydraulic Machinery and Cavitation, 371-380, 1996.

[9] Combès, J.F., Bert, P.F. and Kueny, J.L., "Numerical Investigation of the Rotor-Stator Interaction in a Centrifugal Pump Using a Finite Element Method", Proceedings of the 1997 ASME Fluids Engineering Division Summer Meeting, FEDSM97-3454, 1997.

[10] Torbergsen, E. and White, M.F., "Transient Simulation of Impeller/Diffuser Interactions", Proceedings of the 1997 ASME Fluids Eng Division Summer Meeting, FEDSM97-3453, 1997.

[11] Sato, K., "Blade Row Interaction in Radial Turbomachines", Ph.D. Thesis, Durham University, 1999.

[12] He, L. and Sato, K., "Numerical Solution of Incompressible Unsteady Flows in Turbomachinery", Proceedings of the 3rd ASME/JSME Joint Fluids Eng Conf, FEDSM99-6871, San Francisco, 1999.

[13] Sato, K. and He, L. "Numerical investigation into the effects of a radial gap on hydraulic turbine performance", Proc. Instn Mech Engrs, vol. 215 Part A, 99-107, 2001.

[14] Théroux, E., "Modélisation numérique des écoulements instationnaires dans les turbomachines radiales", Master Thesis, École Polytechnique de Montréal, 2003.

[15] Page, M., Théroux, E. and Trépanier, J.-Y., "Unsteady rotor-stator analysis of a Francis turbine", 22nd IAHR Symposium on Hydraulic Machinery and Systems, June 29 – July 2, 2004 Stockholm - Sweden.

[16] Page, M. and Beaudoin, M., "Adapting OpenFOAM for Turbomachinery Applications", Second OpenFOAM Workshop, Zagreb, 7-9 June 2007 (slides)

1.4 How to get the files

Work in progress ...

1.5 Cases