Studies On Stick-Slip Periodic Vibration Of Dry-Friction Damper Turbine Blades

Blades are the heart of turbomachinery. Their credibility is responsible for the safety of the turbomachinery, even the whole power plant. One of the common structural failures of blades is due to excessive stresses caused by large amplitude vibrations. Friction damper has been used widely to reduce the resonant vibration of turbine blades. More and more manufacturers adapt the damped blades with integral wire or shroud. As the dry friction between the dampers dissipates the vibratory energy, the vibration of blades is reduced. The stick-slip dynamics of dry friction damped blades are discussed in this paper. Part one, the usually problems of turbine blades and the present situation and remaining problems on dry-friction damper are summarized. The model of dry-friction is established and the equations of motion of blade are deduced for forthur analysis.Part two, for a single-dof vibration system excited by a periodic force, friction force is described by a hysteretic model. The method is based on a procedure that uses analytical solution forms for the response within the four intervals where the system possesses a linear vibration characteristic and combines these solutions to form an exact, periodic motion of the system. Numerical simulations show that the resonant vibration of the blade can be well controlled in case the normal pressure applied between damper contacting surfaces is in a suitable value. In addition, introducing the friction damper can also modulate the natural frequency of the blade system, which can avoid the system operated in resonance.Part three, taking into account the coupling of flexion-torsion, the two-dof blade model is studied by the numerical method to obtain the response equations. The influences of the system parameters on the amplitude- frequency curves are discussed. The response of turbine blades under two-phase short circuit is discussed, and find the optimum preload.The normal force between the rubbing surfaces can influence the damping effect of blades. Through the study we found that there is an optimum value for the normal force, under which the vibration of blades can be damped effectively. The damped blades is a nonlinear dynamic system, so its natural frequency can be influenced by external force. The results in this paper show that the dry friction in blades plays a very important role in reducing vibration amplitude of the blades.