Abstract
Axial fans operate in large numbers, often in the close vicinity of humans, therefore reducing their noise is a primary concern. In this paper, beamforming is applied to get information about the location and strength of noise sources on the rotor. This information is invaluable, however, difficult to interpret because of some limitations of the beamforming method. The broadband noise radiated in the upstream direction by an axial fan rotor has been examined by means of a phased array microphone system, and the recorded data have been processed with the use of the Rotating Source Identifier beamforming algorithm. In order to reduce the complexity of the source maps, spatial Fourier analysis has been applied to the beamforming-based circumferential source strength distribution taken at the tip radius of the rotor, where the complexity of the local aerodynamic phenomena makes the evaluation of the aeroacoustic noise source data especially challenging. As part of the processing method, a criterion has been introduced for identifying the significant components of the noise sources. The Fourier analysis enabled the effective enhancement of distinct noise sources out of the beamforming database, despite the presence of signal perturbations and limitations. The noise sources have been located and quantified with use of the Fourier transformation and with help of a criterion based on the physical properties of the noise generation mechanisms.
Highlights
Reducing the noise of axial fans is an important task because of the large numbers of such devices operating in the close vicinity of humans
The broadband noise radiated in the upstream direction by an axial fan rotor has been examined by means of a phased array microphone system, and the recorded data have been processed with the use of the Rotating Source Identifier beamforming algorithm
In order to reduce the complexity of the source maps, spatial Fourier analysis has been applied to the beamformingbased circumferential source strength distribution taken at the tip radius of the rotor, where the complexity of the local aerodynamic phenomena makes the evaluation of the aeroacoustic noise source data especially challenging
Summary
Reducing the noise of axial fans is an important task because of the large numbers of such devices operating in the close vicinity of humans. The phased array microphone technique, supplemented by an appropriate beamforming algorithm, is a valuable tool that uses simultaneously recorded acoustic pressure signals to deliver information on the spatial distribution of noise sources [1, 2]. Using the Rotating Source Identifier (ROSI) [3] algorithm, beamforming can be applied to rotating objects, and spatial source distributions can be obtained e.g. for axial fan rotors. By modifying the geometry, one may be able to reduce noise. Such analysis is reported in [4, 5] suggesting simple design guidelines for noise reduction and efficiency improvement for axial fans. The present investigation, to the aforementioned references, focuses on broadband noise sources
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