Abstract

Perfect detuning of bladed disks is often unfeasible due to their high modal density and the wide spectrum of the excitation forces. An alternative design option to limit resonant blade vibration is the addition of damping originating from dry friction. In the present case, friction damping originates from shrouding at the top of the blade, which interlocks with that of adjacent blades. While the presence of the shroud increases damping, it also affects the dynamic response which becomes nonlinear due to the presence of the displacement-dependent friction contact forces.

In order to assess numerically the damping level of the system during the design phase, ad-hoc numerical tools capable of computing the non-linear forced response of frictionally damped structures must be developed.

For the calculation times to be affordable especially if parametric analyses need to be performed, the size of the original finite element model of the bladed disk is typically reduced through component mode synthesis techniques. The output of such numerical tools is the response at key locations on the blade, but no further indication on the stress levels is obtained. While the response-based evaluation is effective for a comparative analysis, a direct indication of the stress levels is still needed. This work presents a procedure aiming at estimating the stress levels on the blade starting from the result of the nonlinear forced response computation. A stage of a shrouded disk coming from a power generation turbine is used as a test case. Operating conditions including centrifugal load and temperature field are carefully reproduced.