An Improved Correlation for the Broadband Noise of High-speed Fans

Broadband noise data have been obtained from tests on a wide variety of transonic design speed fans. These fans show considerable differences in noise level at a given tip speed which are often inconsistent with trends expected from previous correlations; in particular, fan loading does not appear to be of primary importance. A new correlation has been developed using rotor blade incidence and relative Mach number as primary parameters. The use of incidence accounts for variations in noise between the fans and also for the effects of throttling at constant tip speed, resulting in a good collapse of data. However, the remaining scatter shows that some second-order effects do exist, and these are discussed.