An Experimental Study on Broadband Noise of a Propeller Fan

概要

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The present research is a preliminary attempt towards the prediction of the broadband noise from the flow features, compatible with industrial constraints. In the case of low-solidity impeller, the wake rapidly expands in a wide outer part of the blades under the influence of the separation forced by the tip vortex. The broadband noise level in the low-frequency domain became large because the wake vortices with large scale in the low frequency domain were shed from the blade. Since the relative flow of the high-solidity impeller at the maximum efficiency point remains attached over the blades, the strength of vortex-shedding in the wake is reduced. Therefore the broadband noise at the maximum efficiency point is substantially decreased. At the off-design point in low flow rate, the number of blades has limited influence on the flow regime in the wake because separation likely occurs from the leading edge. In this case, the broadband noise increases with the number of blades.