Investigation of a High-Mach-Number Overexpanded Jet Using Large-Eddy Simulation

An initially laminar overexpanded round jet at an exit Mach number of 3.30 and a Reynolds number of 105 is calculated by compressible large-eddy simulation. The near field obtained by large-eddy simulation is also propagated to the acoustic far field by solving the full Euler equations to take into account the nonlinear propagation effects. Both computations are performed using low-dissipation finite differences in combination with an adaptive shock-capturingmethod. The jet originates from a straight pipe nozzle of radius re, including lips of thickness 0:05re. At the pipe exit, Blasius mean flow profiles are imposed, and static pressure and temperature are equal to 0:5 105 Pa and 360K, resulting in fully adapted and acousticMach numbers, respectively, of 2.83 and 3.47. The jet flowfields, as well as the acoustic near and far fields, are described in detail and compared with data of the literature. The turbulent mechanisms developing in the jet are investigated, using spectral and azimuthal decompositions of the velocity fluctuations along the shear layers. Same analyses are applied to the acoustic fields, in order to discuss the properties of jet noise components. In this way, Mach waves, shock-associated noise, screech tones, and turbulent mixing noise are identified. Nomenclature an = relative contribution of azimuthal modes n c = local sound speed c1 = ambient field sound speed f = frequency fc = cutoff frequency fshock = central frequency of the broadband shock-associated noise fup = frequency of the upstream-propagating shock-associated noise LVS = first shock length from vortex sheet,