Prediction of Turbulent Noise Generated from Counter-Rotating Axial Flow Fans.

Abstract

There are two mechanisms which give rise to turbulent noise radiated from a counter- rotating axial flow fan. 0ne is the strong turbulence induced by the front rotor during the incoming main flow to the rear rotor, which, in turn, induces random force fluctuation on the rear rotor blade. The other is the shedding of vortices from the trailing edge of the both front and rear rotors. In this paper, we take these two mechanisms into consideration to theoretically estimate the turbulent noise level. The estimated values agree well with the measured levels of turbulent noise generated from the counter-rotating fans. It is theoretically clarified that the noise generated from the rear rotor is higher than that from the front rotor. The noise due to the turbulence during the incoming main flow is nearly equal to that due to the vortex shedding from the trailing edge of the rotor.