Dynamic Characteristic Study On Fluid-Structure Interaction For Francis Turbine Runner

Dynamic characteristic of Fluid-Structure interaction (FSI) for Francis Turbine has important influence on optimum design and stable operation of hydraulic turbine both in theory and actual fields. This dissertation mainly studied the rigidity of turbine blade and the effect of deformed runner to the flow field.(1) 3D model of Francis turbine is constructed, the model data file is transferred to rigidity analysis software ANSYS and flow analysis software CFX of CFD, and the computation domain of Francis turbine runner is proposed.(2) Applying the fluid software CFX, based on Navier-Stokes equations and standard turbulence model water pressure on the runner is calculated, by using the method of piecewise computation, the flow field distribution of Francis turbine runner is derived. The blade pressure is loaded onto the runner in ANSYS using APDL language with least error. By CFD research, the stress values at different operating points are obtained, based on which, the water turbine runner rigidity is studied. The research shows that the maximum equivalent stress is observed at such areas as: the joint of crown and outlet of blade, the joint of band and inlet of blade. The stress gradients at these areas are quite large, it tends to cause fatigue failure. The maximal distortion area is the joint of outlet of the runner blade and band, the distortion gets larger from crown to band gradually. In other words this area is the sensitive area of blade vibration. Along with the change of guide vane or turning speed, the maximum equivalent stress position and the stress of runner blade changed greatly.(3)By testing the vibration for the blades of different diameter runner and measuring the frequency, we can get the mode parameters. The turbine runner's frequency was measured in the test, which indicated the blades nature frequency has strong relations with the size and mass distribution of runner. In order to study the vibration mode of blade and runner, vibration mode of the Francis turbine is analyzed with ANSYS. The results shows that the turbine's low-frequency mode shape mainly consists of contortion and swing by crown and band's encircling the shaft, which is the key dynamical parameters in analyzing stress distribution of the dynamical stress for the turbine blades, while the high-frequency mode shape mainly displays the band contorting vibration.(4) New runner model reconstructed by using the distortion plot at every operation point is transferred to CFX , in the later flow field simulations, observe the influence of the distortion. Thus achieve the FSI purpose. The results show that the runner distortion has great effects to the pressure and velocity field of the blade, it can aggravate draft tube turbulence, increase cavitation field.