Experimental and numerical analysis of cavitation and pressure fluctuations in large high head propeller turbine

In the last decades, Computational Fluid Dynamics (CFD) has played an important role in the numerical prediction of cavitation characteristics of different types of hydraulic turbines. Relative results of the characteristics curves for different hydraulic shapes can be predicted very accurately. Usually the prediction of the absolute values of various characteristics is still a challenge. In the paper, we would like to present the comparison between the results of the model testing and numerical analysis of the critical cavitation coefficient for propeller turbine and the results of pressure fluctuation for various operating regimes.

For the numerical analysis, the cavitation model is based on the barotropic state law which describes the density change when the pressure falls below the liquid saturation pressure. Barotropic means that the density depends only on the pressure. The model tests were performed according the IEC 60193 international standards.

The results of the research contain the diagrams with sigma break curves obtained with model test and numerical analysis for different operating regimes. Furthermore, a visual observation of the cavitation on the runner blades is also presented and compared with numerically obtained cavitation regions inside the computational domain. According to the pressure fluctuations full range of operating points has been analysed and are presented. (paper)