Numerical Study Of Vibration Of Hydraulic Turbine Base On Fluid-Structure Coupling

The strong vibrations of Francis hydro turbine unit occur frequently both at home and abroad due to excitation by flowing fluid and the problems of blade cracks of a runner with middle and high specific speed are commonly observed. The vibrations are possibly endangering the safety operation of the unit. However, an effective way to solve the problems has been not obtained so far. Therefore, the study on the hydraulic turbine stability is of great significance. The runner is the key part in the turbine, so the topic mainly studies the runner stability.The interaction between hydraulic turbine blades and viscous flow field is the causes of the vibrations of the blades, and the strong vibrations can lead to the occurrence of fatigue fracture and dynamic loss stability of the blades. Therefore, the study on the dynamic characteristics of the blades is of great significance to understand the flow-induced vibration mechanism, to prevent resonance of the blades, and to ensure safety and stability of the unit.The main works of this thesis are as follows:(1) We build the flowing parts with software UG and numerical simulate the turbine inner flowing. At the same time we get the three kinds of working condition flowing field: large flow,design discharge and small flow. We export the pressure load on the blade to the software ANSYS. Then we translate the model into the ANSYS and obtain the runner and single blade finite element model with the free mesh technology.(2) We analyze the runner and the single blade's static and modal characteristic adopting the sequential coupling method with the software ANSYS. We analyze the possibility which runner and single blade appear resonance in the running state and comparative analysis was done. The results indicate the nature frequencies of runner and single blade is smaller in the water than in the air. The degree of decline is different with the runner structural and vibration mode difference. The decline degrees of single blade's low and high-order nature frequencies are smaller than the middle-order. But the decline degrees of runner's high-order nature frequencies are larger than low and middle-order. The interaction between the fluid and solid not only affect the structural nature frequencies but also change the single blade vibration mode at the same frequencies .In conclusion the interaction between the fluid and solid should be considered when we analyze the hydraulic turbine structural.(3) The affect of centrifugal force and the flow were calculated with the software ANSYS and the results show that the kinds of order frequencies and vibration mode have evident change. The frequencies of single blade and the runner increase with the rotation speed increasing .Moreover, the frequencies change with the flow especially the small flow. The flowing calculation results show that the unit is not steady in the small flow working condition.(4) The software Adina may fulfill the direct interaction. We make full use of the ALE algorithm method, which is good at following the moving boundary between the fluids and solid, to computer the runner's frequency and mode variety under the interaction between the stress and the structural displacement with the software Adina. Comparing the calculation results with the previews research achievement, it approves the reliability of the ALE algorithm method.(5) We discuss several sorts of excitation force which can evoke the unite vibration such as the small vortex in the spiral case, the uneven flowing field after the guide vane, the distribution force of guide vane flow separation vortex and tube vortex band etc. So the above aspects should be seriously considered when we construct the new power station and reform the old power station.