Wake instability past a sphere settling in a strongly stratified fluid
Abstract
The wake of a body moving across the isopycnals of a strongly stratified fluid is characterised by the presence of an intense jet which, under certain circumstances, may become unstable. To get insight into the phenomenology of this instability and the underlying mechanisms, we conduct fully resolved three-dimensional time-dependent simulations of the flow past a rigid sphere settling steadily through a linearly stratified fluid over a wide range of flow parameters which include the case of salt-stratified water. Results reveal a rich dynamics characterised by distinct wake symmetries, vortical structures and transverse force signatures. Simulations evidence the existence of varicose and sinuous instability modes that arise from distinct physical mechanisms. Thanks to several metrics, we build a phase map delineating the bounds of each instability regime as a function of the three control parameters of the problem, namely the Froude, Reynolds and Prandtl numbers. We show that the instability mechanism results from a subtle interplay between baroclinic vorticity generation, vortex tilting and radial transport of the mean density gradient within the jet.
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BibTeX
@article{mo2026wake,
title = {{Wake instability past a sphere settling in a strongly stratified fluid}},
author = {Changfan Mo and Matthieu J Mercier and Jacques Magnaudet and Jie Zhang},
journal = {Journal of Fluid Mechanics},
year = {2026},
month = sep,
doi = {10.1017/jfm.2026.11816},
url = {https://hal.science/hal-05733753v1},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - JOUR
TI - Wake instability past a sphere settling in a strongly stratified fluid
AU - Changfan Mo
AU - Matthieu J Mercier
AU - Jacques Magnaudet
AU - Jie Zhang
PY - 2026
DA - 2026/09/01
JO - Journal of Fluid Mechanics
DO - 10.1017/jfm.2026.11816
UR - https://hal.science/hal-05733753v1
AB - The wake of a body moving across the isopycnals of a strongly stratified fluid is characterised by the presence of an intense jet which, under certain circumstances, may become unstable. To get insight into the phenomenology of this instability and the underlying mechanisms, we conduct fully resolved three-dimensional time-dependent simulations of the flow past a rigid sphere settling steadily through a linearly stratified fluid over a wide range of flow parameters which include the case of salt-stratified water. Results reveal a rich dynamics characterised by distinct wake symmetries, vortical structures and transverse force signatures. Simulations evidence the existence of varicose and sinuous instability modes that arise from distinct physical mechanisms. Thanks to several metrics, we build a phase map delineating the bounds of each instability regime as a function of the three control parameters of the problem, namely the Froude, Reynolds and Prandtl numbers. We show that the instability mechanism results from a subtle interplay between baroclinic vorticity generation, vortex tilting and radial transport of the mean density gradient within the jet.
SN - 0022-1120
SN - 1469-7645
ER -