Study On Simulation Of The Medium-High Specific Speed Francis Turbine Runner's Interblade Vortices

A hydraulic turbine is the core equipment of hydropower stations. The three most important performance indicators: efficiency, cavitation, and stability, are related to the use level of the water, the life and safely running. The runner is the most critical components, which performance will directly affect the turbine performances; and is one of the easily destructive parts in hydropower station accidents because of unsuitable design or irrational running, etc. Therefore,study of runner's flow field and analysis of velocity and pressure, will provide great significance for improving the efficiency and running stability, reducing cavitation and adapting to the development trend to huge scale of morden hydropower units.For a long period, vortex rope in draft tube and Karman vortex are believed to be the primary factor of stability violation. However,as huge Francis hydraulic turbines are widely used, other important factors, such as interblade vortices ,are found to respond the stability. violation.Velocity field, pressure field and pressure fluctuation are simulated based on a specific Francis hydraulic turbine under a number of typical working conditions, and interblade vortices of the runner are studied. The numerical simulation results agree well with the actual situation, which show that the the high head interblade vortices are produced by flow separation at pressure side of the blade near the crown when the turbine is operated at higher head, ,the low head interblade vortices are produced by flow separation at suction side of the blade near the crown when the turbine is operated at lower head. The pressure pulsations of all monitors versus time at diferent position and these amplitudes pectrums versusr fequency were analyzed by FFT to determine the pressure oscillationr fequencies.