Combined acoustic and aerodynamic investigation of the effect of inlet geometry on tip leakage flow noise of free-inlet free-exhaust low-speed axial flow fans

The performance and the emitted noise of a free inlet - free exhaust axial flow fan are influenced by the inlet geometry. In the present paper, the effect of bellmouth entries with various sizes on the tip leakage flow (TLF) noise is discussed. The aerodynamics phenomena are investigated using inlet velocity profile measurements and computational fluid dynamics (CFD) simulations. Noise source maps have been derived from phased array microphone measurements using the Rotating Source Identifier (ROSI) beam forming algorithm. The aerodynamic and acoustic data are evaluated in a combined manner. The results showed that with the use of a bellmouth entry of proper size, the TLF can be moderated, the double leakage flow (DLF) can be eliminated, and the sound pressure level of the emitted noise can be reduced by 5-6 dB. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the impact of varying sizes of bellmouth entries on tip leakage flow noise of a free inlet - free exhaust axial flow fan, utilizing measurements of inlet velocity profile and CFD simulations to analyze aerodynamic phenomena. The results demonstrate that employing a properly sized bellmouth entry can mitigate tip leakage flow, eliminate double leakage flow, and reduce the emitted noise level by 5-6 dB.