Noise emissions from excited jets

Abstract

Exhaust gases emitted from breathing and non-breathing engines are examples of free jet flows, which are encountered in different industrial applications, such as gas turbine engines and rocket motors. Better performance in these applications is associated with higher jet speeds, which implies more noise emissions. This motivated a lot of research to predict and mitigate noise emissions from free jets.

Computational aeroacoustics simulations typically involve issues that might not be significant in traditional computational fluid dynamics. Special attention should be paid to the numerical implementation as we are interested in the noise emission rather than the flow motion or the thermal field. This study numerically investigates the generated noise and perturbations from excited high-speed jets, which are modeled by the linearized Euler equations. We use a fourth-order numerical method, which eliminates any spatial bias in the calculations. The mean flow is prescribed by experimental-analytical approach. Harmonic hydrodynamic excitation is applied at the nozzle exit. The propagation of this excitation is investigated for the pressure (acoustic), velocity, and density waves. We investigate the characteristics of these waves and the differences between them, specially the saturation and decay phenomena. Some features of the noise emission pattern are identified and discussed.

Keywords: noise, excited jets, computational fluid dynamics