Study on vibration characteristics of damping blade with snubber and shroud based on fractal theory

Snubber and shroud have been widely adopted in steam turbine last stage blades to decrease the vibration stress. The contact surfaces between snubber and shroud own obviously fractal geometry characteristics. Based on fractal geometry theory and finite element nonlinear vibration theory, the fractal friction model that describes friction damping contact could be accurately established. In this paper, the contact fractal elements are set up and the nonlinear vibration response characteristics of a long steam turbine last stage blade with snubber and shroud are calculated. The results show that, with the increase of shroud normal force, the resonant amplitude of the blade experiences a decreasing period followed by an increasing period while the modal damping ratio increases first and then decreases when there is only shroud contact. The regulations are similar when there are both shroud and snubber contacts. The resonant frequency increases until the normal contact forces increase to some degree