Investigation of circumferentially non-uniform noise distribution in inlet duct of a one-and-a-half stage axial compressor and its generation mechanism

Accurate measurement of compressor noise imposes specific requirements on number and positions of microphones. However, the effect of microphone number and placement within the pressure field—typically inside the compressor inlet duct—has received little attention. In this study, acoustic experiments were conducted on a 1.5-stage axial compressor—comprising inlet guide vanes (IGVs), a rotor, and a stator—using two pressure-field microphones and thirteen free-field microphones. The noise measurements revealed a circumferentially non-uniform distribution of sound pressure level (SPL) along the inlet duct wall, despite the presence of uniform inlet and outlet boundary conditions. To complement the experiments, unsteady Reynolds-averaged Navier–Stokes (URANS) simulations were performed to predict the unsteady flow field and analyze the superposition of multiple rotor–stator interactions. The results indicate that the coupling of the two rotor–stator interactions in localized regions enhances the local pressure fluctuation. This localized enhancement of pressure fluctuation is identified as the primary mechanism responsible for the circumferential SPL variations in the inlet duct of the IGV–rotor–stator configuration. This finding provides evidence that a single pressure-field microphone at a fixed circumferential position is insufficient for accurately capturing compressor inlet noise levels—even under distortion-free inlet conditions—particularly in multi-row or multi-stage axial compressors.