Noise prediction of a shortcowl jet using energy transfer rate time-scale

Frequency dependency of the defining parameters in aero-acoustics has been a controversial issue and many theoretical and experimental studies have been directed towards its understanding and modelling. In this paper a new time scale based on the turbulent energy transfer rate is introduced and used along with the MGBK method for a short-cowl nozzle. The required CFD results for noise prediction are obtained using a modified k ? e turbulence model. Numerical results are provided for two flow working conditions, bypass velocity ratio 1 and 0.9. Besides the comparisons of the new time scale against the traditional time scale, namely dissipation time scale, corresponding noise prediction results at ninety degrees as well as other angles are compared and discussions are provides. Generally, results show that the new time scale is capable of performing the anticipated frequency dependency and has significantly improved noise prediction, particularly at low and high frequencies