Integral aerodynamic excitations (i.e. forced response) in multi blade row turbomachinery are attributed to a multitude of excitation sources. In a common forced response analysis often only integral excitation orders directly connected to single blade row aerofoil counts and their sums and differences are considered. For the blade row of interest various rotating pressure patterns can occur at a single frequency, which are generated by up- and downstream rotor-stator interactions. These spinning modes - termed Tyler-Sofrin modes - have been described by Tyler and Sofrin [1] from an aero acoustic point of view. The present work considers Tyler-Sofrin modes in axial high pressure compressor forced response analyses. In the first part the effect of rotor stator interactions according to Tyler and Sofrin [1] is presented in detail and put into the context of a forced response analysis of an aerofoil dominated modeshape. This involves the calculation of affected frequencies and nodal diameters. The relevance of considering Tyler-Sofrin modes in the computation of the aerodynamic forcing is described based on the observation of varying blade individual forcing amplitudes over the circumference. In the second part the results of numerical analyses of high pressure compressor multi blade row forced responses addressing the aforementioned set of problems are presented. The results are obtained using unsteady 3D CFD for the computation of the modal forces coming from classical and rotor-stator interaction sources. Vibration responses are calculated using a reduced order model employing a subset of nominal modes (SNM) [2], [3], [4] for a rotor blisk. Various implications of Tyler-Sofrin mode excitations are discussed for tuned and mistuned aerofoil vibrations.
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