Investigation of Sound Generation and Transmission Effects Through the ACAT1 Fan Stage using Compressed Sensing-based Mode Analysis

Abstract

In an extensive measurement campaign at the UFFA test rig of AneCom AeroTest in Wildau, Germany, the sound field generated from the ACAT1 fan stage was measured by several dynamic pressure sensor arrays of different geometrical arrangements at the inlet, interstage and bypass section. The sparse ring arrays with irregular and optimised geometries are utilised in combination with the Compressed Sensing-based mode analysis in order to investigate the tonal and broadband sound generation and transmission with high resolution. From the azimuthal mode spectra, the relation between the cut-on mode range at the sources and the dominant modes at the measurement sections is observed and used to determine the contribution of different sound generation mechanisms. With the help of interstage mode analyses strong rotor-coherent contributions due to rotor wake irregularities are identified and the rotor-shielding effect is assessed. The dependencies of the broadband mode spectra with respect to the operation points and working lines are shown and the contribution of stator and rotor bound sources is investigated. Results indicate that mode scattering at the stator vane row has a significant influence on the downstream radiated sound field. Evidence is further found for the occurrence of the acoustic tunnel effect, where cut-off modes excited at the stator leading edge become cut-on during the propagation through the inter-vane channels. This effect triggers mode scattering towards rotor counter-rotating modes and increases the sound radiation from fan stages.