Hydro Turbine Fluid-solid Coupling Vibration Analysis

The fluid flow induced strong vibrations of Francis hydro turbine unit occur frequently both at domestic and foreign water-power stations. They are ubiquitous that induced structure failure and reduction of turbine operating life, and finally endangered the safety operation of the turbine unit. However, an effective way to solve these problems has not been obtained so far.As a nonlinear dynamic fluid-structure interaction that coupled multi-fields, the vibration problems of Francis hydro turbine unit are extremely complex. The fixed components of Francis hydro turbine play a main role to keep the system work steadily. Therefore, study on the dynamic characteristics of the fixed components is of great significance to understand the flow-induced vibration mechanism, to prevent resonance of the system, and to ensure the safety and stability of the unit.The main works of this thesis are as follows:1. Based on the traits of fixed components of Francis hydro turbine that their geometrical structures are different from each other, this thesis divided the geometry model from its central for several parts to separately build finite element model with software ANSYS. By this way, the whole three-dimensional finite element model can be easily obtained by assembling the separate parts.2. Described and discretized the coupled system that are composed of fixed components of Francis hydro turbine and the incompressible fluid flow in displacement-velocity finite element formulation. And the fluid-structure interaction governing equation was developed by using the Galerkin method. Then, the advancing of added mass and the effect factors of added mass were discussed in detail in terms of the equation's physical meanings.3. According to the vibrating features of the fixed components, the linear coupled system that are composed of fixed components and the compressible fluid flow was described in displacement-pressure finite element formulation and discretized by using Galerkin method to develop governing equations. Took advanced use of the fluid-structure interacting analysis function of software ANSYS, the natural frequencies and mode shapes of the whole fixed components both in air and in water were calculated and the compared. For several characteristic vibration sources, the possibilities of the fixed components to occur resonance under normal operating condition were discussed. Moreover, the effects of the hydraulic pressure on the dynamic characteristics of the system were discussed in detail. The results show that the influence of hydrostatic pressure on the dynamic characteristics of the fixed structure were small, and may be neglected.4. According to the actual damage condition, this thesis reached the conclusion that the possible vibration reason for the turbine is due to the side collision induced by inhomogeneous clearance of the hydro-turbine runner crown seal rings. For this reason, the dynamic responses of fluid-structure interaction system under side collision forces were simulated and analyzed.5. Based on the modal analysis results of fluid-structure interaction system and the influence of water added mass, a new simplified method to calculate the water added mass, which could be obtained by using the interaction system's frequencies in the air and water, was developed with the energy theory and mechanical vibration theory. Moreover, by secondary development technology of ANSYS, the dynamic characteristics of added mass model with variable-mass modal analysis method were realized and the feasibility of added mass method was also further discussed.