Comparison of steady and unsteady simulation methodologies for predicting no-load speed in Francis turbines

- Journal title : International Journal of Fluid Machinery and Systems
- Volume 8, Issue 3, 2015, pp.155-168
- Publisher : Korean Fluid Machinery Association
- DOI : 10.5293/IJFMS.2015.8.3.155

Title & Authors

Comparison of steady and unsteady simulation methodologies for predicting no-load speed in Francis turbines

Hosseinimanesh, Hossein; Devals, Christophe; Nennemann, Bernd; Guibault, Francois;

Hosseinimanesh, Hossein; Devals, Christophe; Nennemann, Bernd; Guibault, Francois;

Abstract

No-load speed is an important performance factor for the safe operation of hydropower systems. In turbine design, the manufacturers must conduct several model tests to calculate the accurate value of no-load speed for the complete range of operating conditions, which are expensive and time-consuming. The present study presents steady and unsteady methods for calculating no-load speed of a Francis turbine. The steady simulations are implemented using a commercial flow solver and an iterative algorithm that relies on a smooth relation between turbine torque and speed factor. The unsteady method uses unsteady RANS simulations that have been integrated with a user subroutine to compute and return the value of runner speed, time step and friction torque. The main goal of this research is to evaluate and compare the two methods by calculating turbine dynamic parameters for three test cases consisting of high and medium head Francis turbines. Overall, the numerical results agreed well with experimental data. The unsteady method provided more accurate results in the opening angle range from 20 to 26 degrees. Nevertheless, the steady results showed more consistency than unsteady results for the three different test cases at different operating conditions.

Keywords

No-load speed;runaway speed;Francis turbine;steady-state simulation;unsteady state simulation;

Language

English

References

1.

Nicolet, C., Arpe, J., and Avellan, F., 2004, "Identification and Modeling of Pressure Fluctuations of a Francis Turbine Scale Model at Part Load Operation," Proceedings of the 22nd IAHR Symposium on Hydraulic Machinery and Systems.

2.

Vu, T. C., and Retieb, S., 2002, "Accuracy assessment of current CFD tools to predict hydraulic turbine efficiency hill chart," Proceedings of the 21st IAHR Symposium on Hydraulic Machinery and Systems, pp. 193-198.

3.

Vu, T. C., Devals, C., Zhang, Y., Nennemann, B., Guibault, F., 2011, "Steady and unsteady flow computation in an elbow draft tube with experimental validation," International Journal of Fluid Machinery and Systems, 4(1), pp. 85-96.

4.

Melot, M., Monette, C., Coutu, A., and Nennemann, B., 2014, "A new standard Francis runner design procedure to predict static stresses stresses at speed-no-load," Hydropower Dams (1).

5.

Hosseinimanesh, H., Vu, T. C., Devals, C., Nennemann, B., and Guibault, F., 2014, "A steady-state simulation methodology for predicting runaway speed in Francis turbines," IOP Conference Series: Earth and Environmental Science, 16(3), 032044.

6.

Ruprecht, A., Helmrich, T., Aschenbrenner, T., and Scherer, T., 2002, "Simulation of vortex rope in a turbine draft tube," Proceedings of the 21st IAHR Symposium on Hydraulic Machinery and Systems.

7.

Guo, C., Wang, G., and Xiao, J., 2009, "Numerical Simulation for Hydraulic Characteristics of Cylindrical Valve in Runaway Protection Process," Proceedings of Power and Energy Engineering Conference, APPEEC. Asia-Pacific, pp. 1-4.

8.

Levchenya, A. M., Smirnov, E. M., and Goryachev, V. D., 2010, "RANS-based numerical simulation and visualization of the horseshoe vortex system in the leading edge endwall region of a symmetric body," International Journal of Heat and Fluid Flow, 31(6), pp. 1107-1112.

9.

Nennemann, B., Vu, T. C., and Farhat, M., 2005, "CFD prediction of unsteady wicket gate-runner interaction in Francis turbines: A new standard hydraulic design procedure," HYDRO 2005 International Conference and Exhibition Villach, Austria.

10.

Kolsek, T., Duhovnik, J., and Bergant, A., 2006, "Simulation of unsteady flow and runner rotation during shutdown of an axial water turbine," Journal of Hydraulic Research, 44(1), pp. 129-137.

11.

Nicolle, J., Morissette, J. F., and Giroux, A. M., 2012, "Transient CFD simulation of a Francis turbine startup," IOP Conference Series: Earth and Environmental Science, 15(6), 062014.

12.

Cherny, S., Chirkov, D., Bannikov, D., Lapin, V., Skorospelov, V., Eshkunova, I., and Avdushenko, A., 2010, "3D numerical simulation of transient processes in hydraulic turbines," IOP Conference Series: Earth and Environmental Science, 12(1), 012071.

13.

Li, J., Yu, J., and Wu, Y., 2010, "3D unsteady turbulent simulations of transients of the Francis turbine," IOP Conference Series: Earth and Environmental Science, 12(1), 012001.

14.

Davidson, P. A., 2004, Turbulence: an introduction for scientists and engineers, Oxford University Press.

15.

Galvan S , Reggio M , and Guibault F, 2011, "Assessment study of k-E turbulence models and near-wall modeling for steady state swirling flow analysis in a draft tube using Fluent," Engineering Applications of Computational Fluid Mechanics, 5, pp. 459-478.

16.

Schlichting, H., and Gersten, K., 2000, Boundary-Layer Theory, MacGraw-Hill.

17.

Bilgen, E., and Boulos, R., 1973, "Functional Dependence of Torque Coefficient of Coaxial Cylinders on Gap Width and Reynolds Numbers," Journal of Fluids Engineering, 95(1), pp. 122-126.

18.

(IEC), I. E. C., 1999, "Nomencluture for hydroelectric powerplant machinery," IEC/TR 61364.