This paper aims at getting a better understanding of the simulative prediction of low engine order excitations in axial compressors. The focus is on the influence of inlet distortions on the forced response of a 4.5-stage research compressor rig. The papers starts with a brief description of the rig. After that the numerical setups required to conduct aerodynamic damping and forced response analyses are presented. Experimental data obtained during a rig test campaign show a significant response of a fundamental mode of the rotor 2 blisk to a low engine order 4. This resonance is studied throughout the paper. A superposition effect of different low engine order 4 sources was observed when changing the clocking of the inlet distortion. The vibrational amplitudes are computed using a subset of nominal system modes model incorporating a measured mistuning distribution. Measured amplitude versus blade patterns are compared with those computed by the aeromechanical models. The observed superposition effect is a key finding and is leveraged to establish comparability of the results.

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