Dynamic Characteristic Analysis Of Kaplan Turbine Blade In Fluid-Structure Interaction

With the size of the kaplan turbine are increasingly growing, the stress of hydraulic turbine transition parts will greatly enhance, and blade cracks increased significantly, which is a serious threat to the safe operation of power plant, so the crack problem and dynamic stress characteristics of turbine blade have widely been paid attention to. Therefore, it is necessary to analyze the dynamic stress characteristics of flow passage components in the hydraulic turbine under the internal flow field to improve operation stability of the unit.In this paper, transient flow field distribution, the dynamic stress and displacement deformation of guide vane and blade based on fluid-structure interaction were carried out, by using three-dimensional unsteady flow field simulation and transient dynamic analysis of the structure, with two way fluid-structure interaction calculation method for single-cycle flow passage on different operating conditions.After considering the effect of fluid-structure interaction, the pressure of the middle section on guide vane pressure surface and suction surface has decreased, with varying degrees of reduction on different working conditions. The pressure difference on blade compared with non-coupling case has been reduced, and the lowest pressure values on blade also decline, which makes the energy performance of blade decreased and will have adverse effects on cavitation performance. In addition, clearance flow in kaplan turbine has been simulated, and a comparative analysis of the changes in flow field before and after the coupling was made.According to calculation results, the maximum equivalent stress on guide vane occurred in the upper and lower face of its junction with the pivot surface by suction or pressure surface side. The maximum displacement deformation of guide vane occurred in the middle of its outlet edge, and the value is very small. The maximum equivalent stress on blade occurred in the junction of propeller shank and flange pivot by the side of blade outlet. Its maximum deformation is at the leaf margin close to the outlet edge of blade. Meanwhile, there are greater differences in the change of dynamic stress on guide vane and blade under various combination operating condition. However, at the condition with the same head and revolving speed, the maximum dynamic stress amplitude of guide vane and blade are different but the same frequency, and their frequency values do not alter following with the changes of guide vane opening and blade angle.Vibration analysis of the model guide vane and blade in the air and water were carried out. The results show that every vibration mode of them in the water is basically the same as its in the air. However, each order frequency in the water decreased, lower than in the air, and the reduction ranges all have non-linear changes in characteristics. The size of the rotation speed has little effect on the natural frequency of blade. So, during the actual running of the unit, we should consider the effect of fluid-structure interaction for hydrodynamic pressure in flow field, and make the natural frequency of flow passage components is far from the excitation force frequency as soon as possible to avoid resonance.