Modeling and Testing Friction Flexible Dampers: Challenges and Peculiarities

This paper deals with the dynamic of blades with strip dampers. The purpose is 1) to present the results of the dynamic numerical calculation, 2) to demonstrate the need for the experimental data on the blade-strip contact to be used as input to the calculation, 3) to propose a new test rig design to obtain them and 4) to test the key components of the new test rig. The forced responses of two blades coupled by a strip damper are calculated at different excitation and centrifugal force values. The dependence of the numerical results on the contact parameter values is confirmed in this significant reference case. The design of a new test rig is then proposed: both the blade frequency response function and the contact hysteresis cycles at the blade-strip contact are measured. It is shown how contact parameters can then be derived from experimental data. The main novelty of the test rig here proposed is the strip loading system, which simulates the uniform pressure distribution provided by the centrifugal force in real operating conditions. This loading system is non-contact and uses compressed air. Classical loading systems which see dead weights directly connected to the strip are assessed and their expected inadequacy is confirmed. The compressed air system is tested by measuring the pressure produced between strip and blades: pressure is uniform across the contact patch, constant in time and its mean value corresponds to realistic pressure values actually experienced by strip dampers during service.