Links Between Steepened Mach Waves and Coherent Structures for a Supersonic Jet

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Links Between Steepened Mach Waves and Coherent Structures for a Supersonic Jet

Pineau, Pierre / Bogey, Christophe

The links between coherent structures in the shear layer of an isothermal Mach 2 jet and steepened Mach waves just outside the jet are investigated using large-eddy simulation. Conditional averages triggered by the detection of high-intensity pressure peaks on a conical surface near the jet flow are computed. Averages obtained for peaks of different intensities are presented to identify the factors favoring the steepened aspect of the waves, which are not likely due to nonlinear propagation effects given the surface radial position. The Mach waves just outside the jet are shown to be correlated with coherent structures in the supersonic side of the mixing layers. Their steepened aspect is found to increase with their intensity. The variations of the wave properties with the convection speed, strength, and geometrical shape of the mixing layer structures are then discussed. These properties do not depend much on the convection speed but are closely related to the two other parameters. The wave intensity and steepened aspect increase because the shear-layer structures are stronger, but also because they are more inclined relative to the jet direction. In the latter case, the asymmetric shape of the structure appears to promote the formation of positively skewed Mach waves.