Efficient forced response analysis for asymmetric vane spacing

Abstract

In the context of forced response analysis, we present a com- putationally efficient method to capture the effect of inflow distor- tions caused by intentional variation of cyclic vane spacing. Ap- plying such configurations is a typical mitigation strategy when unforeseen critical blade vibrations occur due to synchronous excitation by wakes of an upstream row. Altering the circum- ferential distance in a section-wise pattern effectively distributes the fluctuations among several engine order frequencies, thereby reducing their amplitudes. The rotationally asymmetric configu- rations initially call for multi-passage simulations. We show that the circumferential spectrum can be well approximated using single passage results only, without significant additional costs. Our approach is based on an analytically computed Fourier transform of a synthesis functional. For validation, we consider a turbine test case with transonic and subsonic operating points. We determine the reduction in amplitude of dominant inflow modes for an explicitly constructed instance with asymmetric vane spacing and compare our analytical predictions to full-wheel simulations. Furthermore we assess the impact on aerodynamic excitation of downstream rotor blades using both a frequency and a time domain solver.