Influence of Wake and Background Turbulence on Predicted Fan Broadband Noise

Abstract

Next-generation fan designs featuring large bypass ratios have the potential to reduce rotor-stator interaction noise of fans. However, these designs pose new challenges and long-held beliefs regarding the acoustic benefit of such concepts that need to be evaluated. At off-design operating points, the increase in nozzle area serves to maintain the stall margin by reducing the fan loading. To an extent, this may lower the contribution of wake turbulence to fan broadband noise. Therefore, investigating the relative contribution of other noise sources becomes relevant. In this paper, the authors examine the contribution of wake and ingested turbulence to fan broadband noise levels at approach for the ASPIRE fan, which is a next-generation fan concept. To enable the investigation of background turbulence, a Reynolds stress turbulence model is used. The computational fluid dynamics solution then provides inputs for a two-dimensional cyclostationary synthetic turbulence method. The noise predictions are improved by performing simulations at three spanwise positions and by introducing a correction technique to account for the three-dimensional interstage flow. For the investigated case, it is shown that broadband noise generated at the stator is as high as for conventional concepts. Furthermore, both wake and background turbulence contribute significantly to the overall fan broadband noise.