Measurements of fan inflow distortion noise generation in a low speed fan - part II: acoustic analyses

Kurzfassung

In a low speed fan test rig aeroacoustic measurements with different inflow distortions were conducted. The objective of the experimental study is to analyse and better understand the aerodynamic dependencies of the fan noise sources. The mean flow and turbulence characteristics of the inflow distortions are discussed in a companion paper. The present work focuses on acoustic analysis of the inflow distortions as measured with axial and azimuthal microphone arrays. The circumferential position of the axial array is discussed regarding propagation effects in non-uniform flows and turbulent wall pressure fluctuations. In the context of the non-homogeneous turbulence properties, the sound pressure and sound power spectra are interpreted with regard to the dominant broadband noise sources from rotor-stator interaction and inflow-rotor interaction.