Investigation of under-platform damper kinematics and dynamics

Under-platform damper is a device used in turbo engines to attenuate forced vibration amplitude and prevent high cycle fatigue of turbine blades, which are caused by hot gas flow and the vibration of engine rotor. The device itself is a piece of metal and during service it is loaded by centrifugal force against the platform underside of two adjacent blades. The relative movement of the blade platforms produces possible slip on the damper surfaces that dissipates the vibration energy through heat induced by friction. Although the damper is a simple device, it is difficult to predict and optimize its performance in the blades system by combining blade FE model, contact model and kinematic model due to marked nonlinearity of friction force, geometry coupling of two contact surfaces and uncertainties of contact surface conditions. As concluding from literature, the important parameters controlling damper effectiveness include damper mass, friction coefficient, contact stiffness and damper geometry. All numerical models require knowledge or information of contact and friction parameters, which are established either through direct single interface frictional measurements, done with the help of correct test arrangements or by fine tuning the parameters in numerical model and comparing the calculated response against the experimental response of damped blade(dummy or real) in vibration. What happen in detail on the damper kinematics and contact forces on the interface are not experimentally observed. In this thesis, an alternative experimental way of investigating and evaluating under-platform damper behavior is proposed. By measuring relative movement between two simulated platforms, the movement of damper and forces transmitted through the damper, a record of the contact events(stick, slip, separation) which take place during the cycle is expected to provide information of friction coefficient, contact stiffness to better understand the damper behavior. It is paid attention to guarantee that the response determined by damper itself and contact interfaces should not be disturbed by test rig structure. The test rig is a trial to experimentally observe the damper kinematics and contact details , and furthermore reduce the ambiguity and complexity in optimizing damper geometry and performance .