Table of Contents
ISRN Mechanical Engineering
Volume 2012, Article ID 212358, 9 pages
http://dx.doi.org/10.5402/2012/212358
Research Article

Experimental Characterisation of the Far-Field Noise in Axial Fans Fitted with Shaped Tip End-Plates

1Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza University of Rome, 00184 Rome, Italy
2Fläkt Woods Ltd, Colchester CO4 5ZD, UK

Received 29 December 2011; Accepted 24 January 2012

Academic Editor: S. C. M. Yu

Copyright © 2012 S. Bianchi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The authors investigate the far-field noise emissions of a datum fan blade fitted with tip end-plate geometries, originally designed to control the leakage vortex swirl level. The end-plate geometries influence the tip-leakage flow, vortex formation, and swirl level. In doing so, the end-plate geometries influence the sound-power levels. After an evaluation of fan rotors' aerodynamic performance, the study compares the rotors' far-field noise signature characterised in terms of sound-power and pressure-level spectra to enable and assess the end-plate acoustic pay-off. The investigation attempts to establish a cause-and-effect relationship between the tip-flow dynamics and the radiated sound fields, exploring the diverse directivity patterns. The authors found a tonal reduction, due to the enhanced blade-tip end-plates and clarified the relevance of the tip features influencing the radial distribution of the noise sources using coherence analysis. The modified multiple-vortex breakdown end-plate design was effective in reducing the broadband noise, giving an improvement in the frequency range of the turbulent noise.