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Development of experimental test setups for bladed disks and non-linear vibration

Öney, Eren
High-cycle fatigue is one of the most frequent reason of failure for turbomachines and in early design process, so it is crucial to predict the vibration levels. Various finite element modelling techniques for bladed-disk systems appear in the literature, including both reducing large size FEM and describing the frictional contact interface. However, not only having a large size FEM but also including the nonlinear friction to models makes the task very struggling and time consuming. In order to enhance the working life, resonances should be avoided but, it is not easy to avoid all critical resonances on turbomachinery due to the broad spectrum of aerodynamic excitation. Thus, decreasing the vibration amplitudes become necessary. The vibration amplitudes of the system can be reduced by the initial gap and friction between the shroud contact interface which is a nonlinear contact phenomenon. Therefore, calculating the dynamic properties of system is a major problem. This study is conducted in order to understand the nonlinear frictional contact behavior and gap nonlinearity which affects the damping characteristics of the shrouded blades. To do so, two experimental test setups are developed. First one consists of a shrouded blade to measure dynamic responses of stationary shrouded blade with gap nonlinearity. The effects of different shroud contact angle, shroud positions along radial direction, initial gap and different excitation forces are investigated on the first bending mode of the blade. In the second test, an under platform damper setup is prepared. The effect of friction and normal preload at the contact surface is investigated. During both tests, a modal shaker for excitation and a data acquisition system with accelerometers are used for measurement.