Noise of propeller fans used in air-conditioning units

Résumé et principaux résultats

Fans and compressors are the two main noise sources of air-conditioning equipment. This paper deals with the noise radiated by propeller fans of external units of split systems. These fans usually have 3 to 5 large chord blades and are mounted within the unit in front of a heat exchanger. The objective of this work is to improve the knowledge on the acoustic mechanisms of this kind of fans in order to predict and reduce the noise level, especially the broadband noise level which provides the major contribution to the A-weighted OASPL since the BPF tones occur at frequencies usually much lower than 100 Hz. After a short presentation of the main aerodynamic and acoustic characteristics of these fans the paper shows results of tests performed on two 400-mm propeller fans of quite different geometry. These fans have nearly the same performance but their sound power spectra, which depend on the operating point, show some differences which are analyzed. Tests also include the determination of mean flow velocity profiles in a plane closely downstream to the blade trailing edge in order to assess the repartition of the mean load and mean flow along the fan span and try to correlate this information with acoustic performance. Furthermore the measured profiles are compared with those predicted by Fluent code. This comparison appears quite good and confirms that CFD codes are well adapted today for fan performance and mean flow prediction. Flow velocity measurement with a fixed hot film downstream the trailing edge allows to determine the blade wake width at several radiuses along the fan span. These data are used to check the validity of the sound power level prediction from the analytical model of Fukano. This prediction on both fans proves not too bad provided that the tip chord length is accounted for in the model.

Commissions

Machines thermodynamiques

Thème

Conditionnement d'air

Mots-clés

Acoustique, Climatiseurs, Conditionnement d'air, Ventilateurs

Auteurs

GUEDEL Alain