NONLINEAR DYNAMIC MODEL OF A TURBINE BLADE CONSIDERING VIBRATION AND CRACK COUPLING

In order to further investigate dynamic characteristics of turbine runner blades under the coupling effect of vibration and crack, in this article, a runner blade with a crack was taken as the research object. The coupling effect of vibration and crack was analyzed, a nonlinear dynamic model considering the coupling of the runner blade was developed, and the vibration and fatigue characteristics were investigated. First, based on the contact characteristics of the breathing crack surfaces in the runner blade under hydraulic excitation, a breathing crack surface contact model was established. Subsequently, a nonlinear dynamic model considering the coupling effect of vibration and crack was obtained. The crack surface contact force and crack stiffness matrix were established and the vibration and fatigue characteristics were analyzed. Finally, the feasibility of the dynamic model was verified by a case study, and the dynamic and vibration fatigue characteristics under the coupling effect of vibration and crack were revealed. The research results show that with propagation of the crack, the crack surface contact force increases and the dynamic stress amplitude at the crack tip increases contact force acting on the runner blade is close to the natural frequency of the runner blade, a combined resonance will occur. When the coupling effect of vibration and crack is taken into consideration, the vibration fatigue crack propagation model is more accurate and can provide a basis for fatigue strength and life prediction of runner blades.