Experimental development of a measurement technique to resolve the radial distribution of fan aero-acoustic emissions

This paper presents an experimental technique developed to assess the performance of a family of axial fans for compact cooling units. It is used to study fan rotor noise sources to enable the effectiveness of design modifications to be assessed. By varying the radial positions of a near field microphone, correlations with a far field microphone are used to study noise source signatures along the blade span. The correlations reveal distinctive acoustic signatures that are described in detail. The methodology has been shown to be effective in identifying: (i) the blade tip feature with the best acoustic performance; and (ii) other significant noise sources along the blade span.