Author(s)

A. M. Martins & A. C. Mendes

Abstract

This paper deals with the assessment of aerodynamic noise level generated by an industrial ventilation system. The system incorporates an axial flow fan operating with airfoil rotor blades. Measurements were performed using a modular digital sonometer of high precision, equipped with a microphone and a frequency analyser. The procedure that was followed enabled us to account for both the global level and the equivalent frequency level of noise, in the intermediate range of audible frequencies, using a filter of 1/3 of the octave. Keywords: aerodynamic noise, axial flow fans, industrial ventilation systems. 1 Introduction Sound is a form of energy associated with the vibration of material particles in a medium. The displacements of the oscillating particles are transferred throughout the matter as acoustic energy, which travels under the form of a sound wave. Acoustics is the science that studies the generation and transmission of such sound waves. It concerns not only the phenomenon that occurs in air, which is audible to humans, but also other phenomena governed by the same basic laws. Sound may as well be transmitted through solids, liquids and gases. In all cases we are mainly concerned with the study of a wave motion which is, however, very distinct from the motion of the individual particles in the medium. Sound is effectively a mechanical wave motion whose propagation depends on the physical properties of matter. To be transmitted, sound relies on the elasticity and inertia of the material in question [1]. Noise, on the other hand, is a sonorous stimulus that is unpleasant to our hearing and without significant information to its receptor. It can become nevertheless an issue of primary importance in what refers to human health and

Keywords

aerodynamic noise, axial flow fans, industrial ventilation systems.