Experimental Study on the Aeroacoustic Behavior of a Forward-Curved Blades Centrifugal Fan

In this paper, an aeroacoustic study on a forward-curved blades centrifugal fan has been carried out. As a first step, the fan performance curves, i.e., total pressure, power, efficiency and sound power level versus flow rate were obtained, showing its unstable behavior over a wide operating range. Second, the fan sound power level spectra for several working conditions were determined. For this purpose a normalized installation for testing in laboratory was designed and constructed. Afterwards, the velocity and pressure fields, both at the inlet and outlet planes of the impeller were measured using hot wire probes and pressure transducers, for different operating conditions. Finally, the aeroacoustic behavior of the fan was determined measuring the vorticity field at the impeller outlet, which is known to be related to tonal noise generation. This relation is worked out using the theory of vortex sound, developed by several authors during the second half of this century. The paper shows that the generation of tonal noise is produced at the blade passing frequency and it increases with the flow rate. Although the main contribution to fan noise generation is due to mechanical sources, the bands in which aerodynamic noise is generated by these fans correspond to frequencies especially unpleasant to the human ear. Therefore, the research presented in this paper may be of considerable interest, establishing a starting point for the design of quieter and more efficient fans.