On coherent structures in the compressible turbulent round jet

TL;DR

This study uses semi-deterministic modeling to simulate compressible round jets, analyzing how Mach number influences coherent structures, flow instability, and vortex evolution, with results aligning well with experimental data on Strouhal number.

Contribution

It applies a semi-deterministic modeling approach to compressible jets, capturing unsteady flow features and large-scale structures without flow excitation, extending understanding of compressibility effects.

Findings

Strouhal number evolution matches experimental trends across Mach numbers.

Large-scale vortex behavior correlates with previous DNS and experimental results.

The method effectively captures flow unsteadiness and coherent structures in compressible jets.

Abstract

The presence of two-dimensional coherent structures in the near-field of the round jet has been established by several experimental investigations and direct Navier-Stokes simulations (DNS). Their study has a great importance to improve the prediction of unsteady flows dominated by large scale structures. Indeed, coherent structures play a determinant role on turbulence and flow evolution. The goal of this numerical study is to apply the semi-deterministic modelling, a method close to the large eddy simulation (LES), to the simulation of compressible round jets. This allows the simulation of natural unsteadiness without any flow excitation. A free jet configuration is computed for three Mach numbers of 0.3, 0.96 and 1.5 to evaluate the influence of compressibility effects on instability, Strouhal number and expansion rate. There is not quantitative comparisons on flow quantities with experimental data, except for the Strouhal number, due to the discrepancies between the configuration computed here and those experimentally investigated in past studies. The numerical results on coherent structures are validated across a comparison on the Strouhal number of the preferred mode. The results on the evolution of the Strouhal number with the Mach number are in excellent agreement with previous experiments. Moreover, the evolution of the large scale vortices in the flow is well correlated by experimental and DNS results obtained on other configurations.