Experimental determination of the tonal noise sources in a centrifugal fan

In this work, an experimental study about the aerodynamic tonal noise sources in a centrifugal fan with backward-curved blades has been carried out. Acoustic pressure measurements at the fan exit duct and pressure fluctuation measurements on the volute surface have been made for different flow rates. A correlation study of both pressure signals has been made in order to explain some of the features of the aerodynamic tonal noise generation. A strong source of noise caused by the interaction between the fluctuating flow leaving the impeller and the volute tongue is appreciated. The unsteady forces exerted on the fan blades constitute another noise generation mechanism, which affects the whole extension of the impeller, thus transmitting pressure fluctuations to the entire volute casing. The relative importance of this mechanism compared to the impeller–tongue interaction depends on the flow rate.