Investigation of Strouhal number effect on acoustic fields

Understanding how jet flows respond to aerodynamic excitation helps constructing better understanding of the physical aspects of the problem. Also, this might lead to ideas and active techniques to control the induced noise. There are several approaches for noise computations, with different levels of accuracy and computational cost. In this study, we numerically simulate the acoustic field generated from supersonic axisymmetric jet flow. Aerodynamic excitation, or forced oscillatory flow signal, is introduced around the nozzle exit with different Strouhal numbers (nondimensional frequencies) below and above the critical value. Then, the acoustic fields are predicted at these different excitations by integrating the governing equations of the fluctuations. The adopted approach is very efficient in suppressing any spurious waves, except little oscillations during the transient development of the acoustic field at low Strouhal number. The effect of the Strouhal number on the acoustic field is investigated. Big differences in the acoustic fields exist between these cases. Theses differences are highlighted and discussed.