Experimental Study of theTrailingEdge Noise Generated by Axial Flow Fans.pdfVIP

American Institute of Aeronautics and Astronautics 1 Experimental study of the trailing edge noise generated by axial flow fans Alessandro Bongiovì 1 and Andrea Cattanei 2 DIMSET – University of Genova, I-16145 Genova, Italy and Riccardo Ghio 3 Johnson Electric – GATE, I-14100 Asti, Italy An experimental rotor has been expressly realized to study the trailing edge noise generated by axial flow fans and has then been tested in a hemi-anechoic chamber. The rotor blades have has radially stacked profiles based on a NACA 0012 airfoil, resulting in a simple geometry, which prevents complex flows and eases comparisons with noise predictions. Several working points and rotational speeds have been considered yielding a complete data base. The SPL spectra have been scaled according to the similarity rules and then analyzed resulting in typical trends: a broad peak at low blade loading, which grows and moves towards low frequency as the blade loading increases. Finally, the experimental SPL spectra have been compared with those predicted by the Brooks, Pope and Marcolini (BPM) method. The comparisons show a good agreement at the lower blade loadings and rotational speeds but the agreement becomes poorer as both parameters increase. The effect of the rotational speed was unexpected and seems to indicate that, for the present application, some of the BPM correlations should be modified. Nomenclature A = area of the rotor cross section a0 = speed of sound b = blade span c = blade chord, index relative to the blade chord D = shroud diameter, index relative to the shroud diameter D = directivity function d = hub diameter des = index relative to the design conditions F = non-dimensional source spectral function g = function in Eq. (8) f = frequency H = function in Eqs. (3) and (4) I = acoustic intensity K = function in Eq. (5) k = index relative to the k-th 1/3 octave band Ma = Mach number max = index relative to the maximum in the 1/3 oct