High-frequency wavepackets in turbulent jets

• Published in: Journal of fluid mechanics 2017-11, Vol.830, Article R2
• Main Authors: Sasaki, Kenzo, Cavalieri, André V. G., Jordan, Peter, Schmidt, Oliver T., Colonius, Tim, Brès, Guillaume A.
• Format: Article
• Language: English
• Subjects: Acoustics; Computational fluid dynamics; Computer simulation; Decomposition; Dynamics; Flow equations; Fluid mechanics; Formulas (mathematics); Growth rate; Jets; Large eddy simulation; Linear waves; Mathematical models; Noise; Oceanic eddies; Rapids; Solutions; Stability; Strouhal number; Turbulence; Turbulent jets; Velocity; Vortices; Wavelengths; Yields
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2017.659

Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement, in terms of amplitude and phase, with those educed from turbulent jets. Compelling agreement has been demonstrated, for the axisymmetric and first helical mode, up to Strouhal numbers close to unity. We here extend the range of validity of wavepacket models to Strouhal number $St=4.0$ and azimuthal wavenumber $m=4$ by comparing solutions of the parabolised stability equations with a well-validated large-eddy simulation of a Mach 0.9 turbulent jet. The results show that the near-nozzle dynamics can be correctly described by the homogeneous linear model, the initial growth rates being accurately predicted for the entire range of frequencies and azimuthal wavenumbers considered. Similarly to the lower-frequency wavepackets reported prior to this work, the high-frequency linear waves deviate from the data downstream of their stabilisation locations, which move progressively upstream as the frequency increases.