Numerical simulation of different forms of cavitation in Francis turbines
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The document discusses numerical simulation of cavitation in Francis turbines. It presents (1) different forms of cavitation that can occur, such as leading edge cavitation, (2) methods used to model cavitation including the homogeneous model and Zwart mass transfer model, and (3) results showing the model can predict the shape and extent of cavitation and its effects on efficiency and pressure pulsation compared to experiments. The research was funded by the European Union and Slovenian government.
Numerical simulation of different forms of cavitation in Francis turbines
- 1. ANSYS Convergence Conference Ljubljana, 25th of May 2016 Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile Kolektor Turboinštitut, Ljubljana, Slovenia University of Trieste, Italy
- 2. • Turbines – Development of water turbines – Model acceptance testing in accordance with IEC 60193 standard – Site testing • Pumps – Development of pumps – Production, refurbishment and consultancy • Small Hydro Power Plants – Design, manufacturing and installation of small turbines and electro mechanical equipment Kolektor Turboinštitut ACTIVITIES Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 3. Primary aim: to develop reliable, high-fidelity methods for accurate prediction, and optimization, of the performances of hydro-machinery and marine propellers Kolektor Turboinštitut, Slovenia - Company - Development & testing of hydro- machinery (water turbines & pumps) - Manufacturing of small water turbines - CFD/HPC (supercomputer with 2000 cores) University of Trieste, Italy - Experts in num. prediction of cavitation on marine propellers - Experts in optimization - HPC computing ACCUSIM project = Accurate Simulations in Hydro-Machinery and Marine Propellers www.accusim.eu; 1/2/2014-31/1/2018 Knowledge Research Community & Public Dissemination of knowledge + Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 4. Forms of cavitation in Francis turbines: • Leading edge cavitation • Travelling bubble cavitation • Draft tube swirl • Inter-blade vortex cavitation Consequences of cavitation: • Instable flow conditions • Vibrations • Noise • Damage of material surface • Reduction of efficiency Cavitation in Francis turbines Cavitation coefficient: H HHH vsa Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016 Damages of blades due to cavitation
- 5. l M vl m t SP t m )( )( )( 11 U τUU U U volumetotal vapourvolume volumetotal liquidvolume 1 vl vl )1( )1( Homogeneous two-phase model Flow equations: Liquid and vapour volume fractions: Density and dynamic viscosity of the vapour-water mixture: Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 6. Cavitation Zwart mass transfer model Rayleigh-Plesset equation: v l v B v v l v B vnuc PP P PP R PP P PP R r m if 3 23 F if 3 2)1(3 F- c e rnuc=5×10-4, RB=2×10-6 m, Fe=50, Fc=0.01 Fe=300, Fc=0.03 Nucleation site volume fraction: Radius of a nucleation site: Default evaporation and condensation constants: On NACA66 hydrofoil calibrated constants: (Morgut, M., Nobile, E. and Biluš, I. Comparison of mass transfer models for the numerical prediction of sheet cavitation around a hydrofoil. Int. Journal of Multiphase Flow. Vol. 37. No. 6. 2010. pp. 620- 626. Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 7. Cavitation at full load: • leading edge cavitation, • traveling buble cavitation • draft tube swirl Absolute pressure Experiment The shape and extend of extent of cavitation (Iso-surface of Vapour Volume Fraction = 0.3) σ = 0.154 σ = 0.115 σ = 0.098 Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016 The shape and extent of cavitation Isosurfaces of Vapour Volume Fraction =0.3
- 8. σ = 0.180 σ = 0.154 σ = 0.128 σ = 0.115 σ = 0.098 Standard constants Tuned constants Figure 6: Distribution of water and vapour at the suction side of one runner blade Regions of cavitation on suction side of runner blades Standard constants (CFX): Evaporation coefficient Fe = 50, Condensation coefficient Fc = 0.01 Tuned constants: Fe = 300, Fc = 0.03 Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 9. Draft tube swirl - Cavitating vortex rope in the draft tube at different operating regimes Part Load High Load Q/QBEP = 0.66 Q/QBEP = 0.8 Q/QBEP = 0.85 Q/QBEP = 1.15 Experiment Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016 Numerical simulations without cavitation modeling Previous results without cavitation modeling: LIPEJ, Andrej, JOŠT, Dragica, MEŽNAR, Peter, DJELIĆ, Vesko. Numerical prediction of pressure pulsation amplitude for different operating regimes of Francis turbine draft tube. V: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27-31, 2008, Foz do Iguassu, Brazil.
- 10. Configuration Spiral casing, stay and guide vanes Runner Draft tube Total 1 1,400,000 1,500,000 900,000 3,800,000 2 1,400,000 12,600,000 3,000,000 17,000,000 3 - 12,600,000 12,400,000 25,000,000 Number of nodes in particular geometry configuration Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile Ljubljana, 25th of May 2016 Operating point Exp. values Numerical values for different configurations 1 2 3 OP1 3,20 Hz 3,09 Hz 3,22 Hz - OP2 4,00 Hz 4,01 Hz 3,95 Hz 3,80 Hz OP3 4,10 Hz 3,80 Hz 3,82 Hz - OP4 4,45 Hz - - - Pressure pulsation at part load Previous results without cavitation modeling: LIPEJ, Andrej, JOŠT, Dragica, MEŽNAR, Peter, DJELIĆ, Vesko. Numerical prediction of pressure pulsation amplitude for different operating regimes of Francis turbine draft tube. V: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27-31, 2008, Foz do Iguassu, Brazil. Pressure pulsation frequency
- 11. Cavitating vortex rope at part load • Operating point: Q/QBEP = 0.8, y/yBEP = 0.97 • Turbulence model: SAS SST • Advection scheme: HRS • Time step: 2 deg. of runner revolution • Homogeneous model, default evaporation and condensation constants Input data: geometry, head, rotating speed Output: flow rate, torque on the shaft, efficiency, pressure pulsation Pressure pulsation measurement Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016 Number of nodes Spiral casing, stay and guide vanes Runner Draft tube Total 1,400,000 1,500,000 2,500,000 5,400,000
- 12. Experiment Simulation without cavitation modelling Simulation with cavitation modelling Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 13. Conclusions: • Different types of cavitation in Francis turbines can be numerically predicted. • The effect of cavitation on turbine efficiency is quite accurately predicted, with slightly premature drop of efficiency curve. • The accuracy of calculated amplitudes of pressure pulsation, caused by cavitating vortex rope at part load is improved if cavitation is included in simulation. Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 14. Acknowledgements The research was funded by the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013/ under REA grant agreement n°612279 and Slovenian Research Agency ARRS, Contract No. 1000-09-150263 Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016
- 15. Thank you for your attention ! Numerical simulation of different forms of cavitation in Francis turbines D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile ANSYS Convergence Conference, Ljubljana, 25th of May 2016