Validation of a Modal Work Approach for Forced Response Analysis of Bladed Disks

The paper describes a numerical method based on modal work approach to evaluate the forced response of bladed disks and its validation against numerical results obtained by a commercial FEM code. Forcing function caused by rotor/stator interactions are extracted from CFD unsteady solution properly decomposed in time and space to separate the spinning perturbation acting on the bladed disk in a cyclic environment. The method was firstly applied on a dummy test case with cyclic symmetry where the forcing function distributions were arbitrarily selected: comparisons for resonance and out of resonance conditions revealed an excellent agreement between the two numerical methods. Finally, the validation was extended to a more realistic test case representative of a low pressure turbine bladed rotor subjected to the wakes of two upstream rows: an IGV with low blade count and a stator row. The results show again a good agreement and suggest to compute the forced response problem on the finer CFD blade surface grid to achieve a better accuracy. The successful validation of the method, closely linked to CFD environment, opens the opportunity to include the tool on an integrated multi-objective procedure able to account for aeromechanical aspects.