ACTRAN numerical study on the effects of intake geometry and length on fan tone noise propagation and radiation

Abstract

In this study, the geometry of a drooped intake of a scale rig for typical turbofan engines is artificially modified to create fictitious shorter intake geometries in order to investigate the impact of the intake length on the forward radiated fan noise. The study has been conducted by using three-dimensional ACTRAN TM models, and computations were performed over a wide range of frequencies. The noise source of interest is buzz-saw tones, hence rotor-locked single mode at the fan plane at integer-multiples of the engine shaft rotation speed at each engine order was used to define the noise source. In parallel, ACTRAN TM predictions by using the axisymmetric models generated based on the sideline profile of the drooped intake have also been performed for comparison and understanding the three-dimensional effect on the radiation directivities. The ACTRAN results show that the impact of the intake length is quite small if the intake is not acoustically lined. In case of lined intake, however, the far-field directivity can be significantly modified by the change of the intake length. <br/