Influence of foam-resin lining on the reflections and scattering of acoustic modes at pylons in a flow duct

Kurzfassung

In the exit duct of a fan test bench, unwanted reflections and scattering of the acoustic modes radiated by the fan occur at three construction-related pylons. These lead to a distorted analysis of the fan sound excitation. The aim of an experimental study is to develop a cost-effective measure to reduce the reflections and scattering. The effect of various sound-attenuating linings made of melamine resin foam on the pylons, optionally in combination with a duct liner, was investigated. To do this, individual duct modes were generated using a loudspeaker array and radiated onto the object under investigation. The achieved attenuation was determined by applying a radial mode analysis to a microphone array placed between the loudspeaker array and the object under investigation. The presentation shows that the reflections depend strongly on the propagation angle of the modes and that the scattering increases in particular near cut-on frequencies. The different effects of the examined configurations are discussed.