Cavitating flow simulations and experiments on Francis turbine model
Wang Lei1, Lou Yu2, Wang Zhaofu1
1.Institute for Hydroelectric Technology, Huadian Electric Power Reasearch Institute, Hangzhou, Zhejiang 310030, China; 2. Science and Technology Promotion Center Ministry of Water Resources, Beijing 100038, China
Based on a two-phase cavitation flow model, both steady and unsteady cavitating flows in a model of 1 000 MW Francis turbine for Baihetan hydropower station are carried out, and the predicted cavitation performance and pressure pulsation are compared with the measured ones. In steady cavita-ting flow simulations, the total pressure of stream in the draft tube is lowered step by step, causing a steadily reduced cavitation coefficient available so as to mimic cavitation progress in an experiment on the model. The features of cavitation development, cavity locations and evaluation of cavitating vortex rope in the draft tube have been predicted well by means of pressure distribution, velocity vector and vapour volume fraction. Additionally, unsteady cavitating flow simulations can predict temporal variations of the cavities and vortex rope as well as the frequencies of pressure fluctuation precisely; consequently, the vibration frequency and amplitude estimated are consistent with the experimental data. It is shown that vortex rope in the draft tube can affect the pressure pulsation and instability of the turbine more significantly with the development of cavitation. In other words, the pressure pulsation is more sensitive to cavitation, i.e. the more serve cavitation, the more violent pressure pulsation, and cavitation intensifies the hydraulic turbine instability.
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