Prediction of the influence of the cavitation on the performance of a Kaplan turbine
PhD thesis under the supervision of:
- Régiane FORTES PATELLA (LEGI) ;
- Guillaume BALARAC (LEGI) ;
- Antoine BOMBENGER (GE Renewable Energy-Grenoble).
Abstract
The presence of cavitation phenomena in hydraulic machines cause several structural damages and alter the machine performances. Hence, the investigation of the cavitation in hydraulic turbine is of great industrial interest. Among the hydraulic turbine, Kaplan turbine are known for their flexibility. The guide vane opening and the runner blade position can be continuously regulated during machine operation maximizing the efficiency for a large range of operating conditions. This implies the presence of shroud and hub gaps that leads to additional cavitation structures in the runner. In this context, the principal aim of this thesis is the development of a numerical methodology able to predict and characterize the cavitation in Kaplan turbine and its impact on the machine performance. The analysis refers to a scale model of a 5-blades Kaplan turbine. RANS/URANS equations have been solved modeling the cavitating flow by using a homogeneous approach and a barotropic state law. The methodology have been defined for optimal operating conditions and, after has been tested also on the full load operating point. Experimental data have been used to validate the developed numerical method of cavitation prediction. The numerical predictions of the performances and the vapor structures obtained by applying the new cavitation calculations strategy are in very good quantitative and qualitative agreement with the available experimental data. Once the numerical methodology has been defined in-deep analyses of the cavitating flow evolution in the machine have been performed. The developed approach appears to be very reliable, robust and precise.
Keywords:
Kaplan turbines, Cavitation, Performance analysis, RANS/URANS simulations, Hydroelectric energy