Broadband sound power determination in aeroengine duct with respect to modal decomposition

In this paper an experimental technique for the decomposition of broadband ducted sound fields into their mode constituents is applied to a real low speed fan test rig, which enables not only the calculation of in-duct transmitted sound power for dominant tones, but also broadband noise over a wide frequency range. The broadband mode analysis technique is based on spectral coherences using wall-flush installed pressure sensors as well as radial sensor rakes in the flow. The broadband sound power determination method was experimentally verified in a low speed fan test rig in Northwestern Polytechnical University. The experimental setup consists of a single-stage compressor in a flow duct. For mode detection 16 microphones were installed in the duct, a microphone mounted near the rotor was used as a reference sensor. Experimental results are presented for four operating conditions.