A Numerical Study on Fan Tonal Noise Induced by Rotor-Stator Interaction

Abstract

For high-accurate prediction of fan tone noise, unsteady flow-field around single stage fan used in an experiment was numerically analyzed with a CFD code based on Unsteady Reynolds-Averaged Navier-Stoke equations. The pressure fluctuations with Blade Passing Frequency (BPF) and their higher order components were extracted by Fast Fourier Transform (FFT). These pressure fluctuations were decomposed into circumferential acoustic modes and radial modes by FFT and Bessel functions. It was confirmed that the circumferential mode of the pressure waves generated by the interaction between the rotor wakes and the stator vanes agreed with theoretical one. By the radial mode analyses, it was found that the waves propagating upstream of the stator vanes decayed and scattered into higher order BPF waves while when those waves interacted with the rotor blades. From these results, the behavior and structure of three-dimensional waves are revealed.