Challenges of numerical noise prediction in a lined turbofan nacelle

摘要

In this paper, the authors describe the challenges in numerically predicting turbofan nacelle noise propagation with an acoustic liner. The combination of modern high bypass ratio turbofans and nacelle is the current key in designing quieter technology. With evident and continual need to minimize the impact on community (mainly around airport) and interior (inside the cabin) noise, technical implementation and numerical prediction are more and more challenging. The paper will emphasize on numerical prediction of turbofan nacelle noise for ultimate quieter aircraft. As instance, complex difficulties appear when high speed flow is considered as during take-off and cut-back condition. At those conditions, nacelle designers have to deal with tiny acoustic wave length scale due the high speed flow regime, non-linear effect mainly due to the high sound pressure level as well as blade to blade difference responsible to buzz-saw noise generation. For aircraft manufacturing, everlasting battle with weight also stimulate new concept of acoustic liner. Smoothness of the acoustic treatment has been reported and shows great noise reduction, and will be also discussed as well as 3-D geometry effects. The prediction capabilities from simple to most complex models are made huge progress. The challenge becomes more and more fulfilled with several others aspects: 1) source assumptions made in measurement and in predictive tools 2) tone, broadband noise 3) wide range of frequencies 4) (turbulent) boundary layer, etc… Nevertheless, the authors will show examples of current research activities in dealing with such complexities.