Jets in stratified flows are ubiquitous in geophysics. A fundamental question is whether the instabilities and coherent structures generated by the flow interact with the physical boundaries and, if so, how. To this end, a simple canonical model flow is employed: a parallel Bickley jet confined between walls in a uniformly stratified fluid. We first show that short wavelength Kelvin-Helmholtz instability can generate asymmetry in the mean flow. Although the fluctuations decay rapidly away from the jet, the asymmetric mean flow does not. We then examine long-wavelength coherent structures that can emit internal gravity waves, which decay slowly towards the walls or, in some cases, radiate away from the jet. These waves transport momentum and distort the mean flow, reducing the jet centreline velocity significantly. When radiation occurs, whether the instability persists at high Reynolds numbers depends strongly on the boundary conditions imposed at the walls. Moreover, we found an instability and associated nonlinear coherent structures that persist at Richardson numbers above the Miles-Howard criterion. The existence of this viscous mode does not rely on the presence of the walls.
Internal solitary waves (ISWs) are known to induce material transport through various mechanisms, with important implications for physical and ecological processes. We report direct numerical simulations of an ISW under conditions favorable for the development of a subsurface core, a situation particularly suitable for...
Chi-Chi Zhou, M. Stastna· The Physics of Fluids· 0 citations
Abstract Content of image described in text. In the ocean, internal wave beams are generated by the barotropic tide passing over steep topography. Observations suggest that these wave beams are dissipated as they propagate into the upper ocean. This differs from idealised numerical simulations of wave propagation, in w...
Arefe Ghazi Nezami, Alexis K. Kaminski, D. Lecoanet et al.· Journal of Fluid Mechanics· 0 citations
Abstract Content of image described in text. In Hass & Lele (2026 J. Fluid Mech. 1037, A20), we looked at the statistical structure (self-similarity) and entrainment rate of a shear-free turbulent layer bounded by a net zero momentum source layer above and a stable density interface below and found agreement with oscil...
Ryan Hass, S. Lele· Journal of Fluid Mechanics· 0 citations
Abstract Content of image described in text. Pipe flow controlled by streamwise-travelling waves of azimuthal wall velocity is studied using direct numerical simulations at a bulk Reynolds number italic Re Subscript b Baseline equals 4900 Reb=4900
$\textit{Re}_b=4900$
. A comprehensive analysis of drag reduction shows...
E. Gallorini, D. Massaro, Philipp Schlatter et al.· Journal of Fluid Mechanics· 0 citations
Abstract Content of image described in text. A weakly nonlinear theory is developed for shock cells in an imperfectly expanded axisymmetric supersonic jet. By adopting a jet profile with a finite-thickness shear layer and a high-Reynolds-number asymptotic formalism, the shock cells are treated at leading order as a sup...
Zheng-Xuan Song, Yi-Hong Fang, Zhongyu Zhang et al.· Journal of Fluid Mechanics· 0 citations
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