Transition from shear-dominated to Rayleigh-Taylor turbulence
Artikel i vetenskaplig tidskrift, 2021

Turbulent mixing layers in nature are often characterised by the presence of a mean shear and an unstable buoyancy gradient between two streams of different velocities. Depending on the relative strength of shear versus buoyancy, either the former or the latter may dominate the turbulence and mixing between the two streams. In this paper, we present a phenomenological theory that leads to the identification of two distinct turbulent regimes: an early regime, dominated by mean shear, and a later regime dominated by buoyancy. The main theoretical result consists of the identification of a cross-over timescale that distinguishes between the shear- and the buoyancy-dominated turbulence. This cross-over time depends on three large-scale constants of the flow, namely, the buoyancy difference, the velocity difference between the two streams and the gravitational acceleration. We validate our theory against direct numerical simulations of a temporal turbulent mixing layer compounded with an unstable stratification. We observe that the cross-over time correctly predicts the transition from shear- to buoyancy-driven turbulence, in terms of turbulent kinetic energy production, energy spectra scaling and mixing layer thickness.

shear layer turbulence

stratified turbulence


Stefano Brizzolara

Eidgenössische Technische Hochschule Zürich (ETH)

Swiss Federal Institute for Forest, Snow and Landscape Research

Jean-Paul Mollicone

Imperial College London

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

Maarten van Reeuwijk

Imperial College London

Andrea Mazzino

Università degli Studi di Genova

Istituto Nazionale di Fisica Nucleare

Markus Holzner

Swiss Federal Institute for Forest, Snow and Landscape Research

Eawag - Swiss Federal Institute of Aquatic Science and Technology

Journal of Fluid Mechanics

0022-1120 (ISSN) 1469-7645 (eISSN)

Vol. 924 A10


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