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

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.

Authors:

• Raza Abdulla Saeed

Keywords:

• Computational Fluid Dynamics
• Hydraulic Francis Turbine
• Numerical Simulation
• Two-Phase Mixture Cavitation Model.

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.