Imprint of Vortical Structures on the Near-Field Pressure of a Turbulent Jet

The distributions of turbulent scales in a Mach 0.9 isothermal round jet are investigated for the purpose of developing linear surface-based models for the noise source that can be informed by a Reynolds-averaged Navier-Stokes (RANS) solution of the flowfield. The jet is calculated by large-eddy simulation (LES), which enables the computation of two-point space-time correlations throughout the jet and its near-acoustic field. Time, length, and convective-velocity scales are examined on the surface of peak Reynolds stress (SPS), representing the location of the most energetic eddies, and on a radiator surface at the boundary between the rotational and irrotational fields. The nature of the space-time correlations is different for axial velocity fluctuations and pressure fluctuations. Velocity-based correlations appear to capture localized turbulent events, whereas pressure-based correlations appear dominated by the interaction of large eddies with the surrounding potential flow. The correlation length scales are larger on the radiator surface than on the SPS, thus indicating that small-scale eddies do not make a significant imprint on the radiator surface. The scales associated with an emulated RANS solution of the flow are compared to the LES-based scales. Simple relationships are inferred that may aid the development of rapid predictive models.

Automated summary

The study investigates the turbulent scales in a Mach 0.9 isothermal round jet to develop linear surface-based noise source models informed by a Reynolds-averaged Navier-Stokes (RANS) solution. Different space-time correlations are observed for axial velocity fluctuations and pressure fluctuations, with small-scale eddies showing minimal impact on the radiator surface. Simple relationships are inferred to aid the development of rapid predictive models.