Numerical Simulation of Sound Emission from Supersonic Jet

TLDR: In this article, the behavior of a supersonic jet was analyzed by performing numerical simulation under various flow conditions to explore the mechanism of sound emission from the jet, and the results showed that the dynamics of vortices plays a key role in sound emission.

Abstract: The present paper addresses the behavior of supersonic jet by performing numerical simulation under various flow conditions to explore the mechanism of sound emission from the jet. In the simulation, an accurate numerical code is used; that is, the fourth order upwind scheme in spatial discretization to reduce numerical dissipation, and a third order Runge-kutta method in time integration. In this study we are interested in the effects of nozzle exit pressure on the breakdown of jet as well as the difference in jet properties between 2D and 3D calculations. Specifically, four cases were simulated. As a result, a clear shock-cell structure was observed with a Mach disk inside the jet in under-expanded cases. Furthermore, it was found that the dynamics of vortices plays a key role in sound emission. The discernible pressure waves commonly referred to as Mach wave emission are recognized, which stems from around a pair of moving vortices. Furthermore, another kinds of wave were found to propagate toward the upstream, which seems to be related with a screech tone. These waves interact with jet shear layer in a complicated manner We are also interested in the three-dimensionality intrinsic in jet. It is observed that the jet has some helical modes in its transition. These features affect the properties of radiated waves. Finally, one of the present results was well compared with the experimental data.