Simulation and Modeling of Turbulent Jet Noise

Jet noise reduction remains an important long-range goal in commercial and military aviation. Comparedwith their early counterparts, modern, ultrahigh-bypass-ratio turbofans on commercial aircraft are very quiet, but evermore stringent noise regulations dictate further reductions. In addition, hearing loss bypersonnel and community noise issues are prompting the military to seek noise reduction on future tactical aircraft. Further increase in bypass ratio not being a practical option, military applications in particular call for nuanced approaches to noise reduction including mixing devices like chevrons or even active noise control approaches using unsteady air injection. In this paper, we briefly review some recent developments in theoretical, experimental and computational approaches to understanding the sound radiated by largescale, coherent structures in jet turbulence that might guide these noise reduction efforts.