Numerical Simulation of Three-Dimensional Cavitating Turbulent Flow in Francis Turbines with ANSYS

Authors: Raza Abdulla Saeed

Abstract:

In this study, the three-dimensional cavitating turbulent flow in a complete Francis turbine is simulated using mixture model for cavity/liquid two-phase flows. Numerical analysis is carried out using ANSYS CFX software release 12, and standard k-ε turbulence model is adopted for this analysis. The computational fluid domain consist of spiral casing, stay vanes, guide vanes, runner and draft tube. The computational domain is discretized with a threedimensional mesh system of unstructured tetrahedron mesh. The finite volume method (FVM) is used to solve the governing equations of the mixture model. Results of cavitation on the runner’s blades under three different boundary conditions are presented and discussed. From the numerical results it has been found that the numerical method was successfully applied to simulate the cavitating two-phase turbulent flow through a Francis turbine, and also cavitation is clearly predicted in the form of water vapor formation inside the turbine. By comparison the numerical prediction results with a real runner; it’s shown that the region of higher volume fraction obtained by simulation is consistent with the region of runner cavitation damage.

Keywords: Computational Fluid Dynamics, Hydraulic Francis Turbine, Numerical Simulation, Two-Phase Mixture Cavitation Model.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1109995

References:

[1] U. Dorji, R. Ghomashchi, “Hydro turbine failure mechanisms: An overview,” Engineering Failure Analysis, vol. 44, pp. 136-147, 2014.
[2] P., Kumar, R. P. Saini, “Study of Cavitation in Hydro Turbines a Review,” Renewable and Sustainable Energy Reviews, vol. 14, no. 1, pp. 374–83, 2010.
[3] L., Zhang, J. T. Liu, Y. L. Wu and S. H. Liu, “Numerical simulation of cavitating turbulent flow through a Francis turbine,” 26th IAHR Symposium on Hydraulic Machinery and Systems, pp. 1-7, 2012.
[4] X. Escaler, E. Egusquiza, M. Farhat, F. Avellan, “Detection of cavitation in hydraulic turbines”. Mechanical Systems and Signal Processing 20, pp. 983-1007, 2006.
[5] H.-J. Choi, M. A. Zullah, H.-W. Roh, P.-S. Ha, S.-Y. Oh, and Y.-H. Lee, “CFD validation of performance improvement of a 500 kW Francis turbine,” Renewable Energy, vol. 54, pp. 111–123, 2013.
[6] D. Jošt, A. Lipej, P. Mežnar, "Numerical prediction of efficiency, cavitation and unsteady phenomena in water turbines," ASME 2008 9th biennial conference on engineering systems design and analysis, pp.157- 166, 2008.
[7] S. Bernad, S. Muntean, R. Resiga, I. Anton, “Numerical analysis of the cavitating flows,” Proceedings of the Romanian Academy A, vol. 7, no. 1, pp. 33-45, 2006.
[8] R. Resiga, S. Muntean, S. Bernad, I. Anton, “Numerical Investigation of 3D Cavitating Flow in Francis Turbines.” Proceedings of the Conference on Modelling Fluid Flow 2, pp. 950-957, 2003.
[9] M. Sedlar, P. Zima, M. Muller, "CFD Analysis of Cavitation Erosion Potential in Hydraulic Machinery," Proc. 3rd IAHR WG Meeting, pp. 205-21, 2009.
[10] F. Avellan, “Introduction to cavitation in hydraulic machinery”, Proceedings of 6th International Conference on Hydraulic Machinery and Hydrodynamics, Timisoara, Romania, pp.11-22, 2004.
[11] G. Wang, I Senocak, W. Shyy, “Dynamics of attached turbulent cavitating flows,” Progress in Aerospace Sciences, pp. vol. 37, pp.551– 581, 2001.
[12] R. A. Saeed, A. N. Galybin, V. Popov, “3D fluid-structure modelling and vibration analysis for fault diagnosis of Francis turbine using multiple ANN and multiple ANFIS,” Mechanical Systems and Signal Processing, Vol. 34, no. 1-2, pp. 259-276, 2013.
[13] D. Jost, A. Lipej, “Numerical prediction of non-cavitating and cavitating vortex rope in a Francis turbine draft tube,” Strojniski vestnik-Journal of Mechanical Engineering, Vol. 57, no. 6, pp. 445-456, 2011.