What is it about?
This article describes the noise sources in low speed fans (through a typical automotive engine cooling fan), and how these sources vary with the flow condition. Variations due to manufacturing are also tackled. Noticeably, the effect of flow conditions on subharmonic humps (broadband narrow humps that appear in the noise spectra at frequencies below the blade passing frequency) is studied, and the physical understanding of their origin is unveiled for the first time. It can also be concluded that the main broadband noise contributor at design and lower flow rates in such rotating machines is tip noise.
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Why is it important?
For the first time, the subharmonic humps in the acoustic spectra of low speed fans are explained. These humps can be the major noise contributors in such rotating machines even at the design condition. As a corollary, this article proves that tip noise is also the dominant brooadband and overall noise source in such machines.
Perspectives
The main perspective is noise control: by controlling the formation of coherent structures in the tip gap and possibly their rotational speed, this major noise source can be elininated or mitigated.
Professor Stéphane Moreau
Universite de Sherbrooke
Read the Original
This page is a summary of: Sub-harmonic broadband humps and tip noise in low-speed ring fans, The Journal of the Acoustical Society of America, January 2016, Acoustical Society of America (ASA),
DOI: 10.1121/1.4939493.
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