Prediction of the tonal noise radiation of an axial flow fan located downstream of a Bluff Body

Abstract

This paper investigates the tonal noise radiated by a subsonic axial flow fan when installed downstream of a bluff body. Typically industrial axial flow fans operate in cluttered environments, and are usually driven through direct coupling from an engine. For this investigation, the fan is located in a knife-edged shroud and placed downstream of a bluff body having representative dimensions of a typical engine. Axial flow fans in general radiate broadband and discrete frequency noise, the latter of which modelling efforts are maturing. The numerical simulation is based on the aero-acoustic analogy where the unsteady flow is first computed using CFD and then passed to a BEM solver to compute the acoustic radiation. URANS and DES methods are examined for the turbulence modelling. The time-varying force on a single blade in the CFD solver over one complete rotation is used to construct the equivalent fan source in the BEM model. Experimental measurements of Sound Pressure Level are performed in a hemi-anechoic chamber, and a comparison between numerical predictions made. This numerical procedure can be used to further aid designers in understanding the effects of fan tonal noise in cluttered environments.