Potential-enstrophy lengthscale for the turbulent/nonturbulent interface in stratified flow
File(s)
Accepted version
Author(s)
Boetti, Marco
van Reeuwijk, Maarten
Liberzon, Alexander
Type
Journal Article
Abstract
We study properties of the turbulent/nonturbulent interface (TNTI) between two layers of stratified fluids through direct numerical simulations (DNSs). Zero mean shear forcing creates moderate turbulence in one of the layers with the Taylor microscale Reynolds numbers in the mixed region of
Re
λ
=
35
,
44
. We focus on the similarities and differences of the properties of stratified TNTIs due to two distinct types of forcing: (a) convection due to a boundary heat source and (b) agitation resembling a vertically oscillating grid experiment. Similarly to other stratified flows, the small scale dynamics of the TNTI in the present DNSs differ from what would be expected in comparable yet unstratified TNTIs. The interface cannot be indeed uniquely identified by the commonly used vorticity
ω
. Instead, the potential enstrophy
Π
2
is shown to be the most appropriate marker in these flow cases. It is emphasized that the Kolmogorov lengthscale
η
K
∼
√
ν
/
ω
is not representative of the small scale dynamics of the interface. Hence, an alternative lengthscale,
η
Π
, is defined, in analogy to the Kolmogorov scale, based on the potential enstrophy,
η
Π
=
(
ν
3
/
Π
∗
)
1
/
6
, being
Π
∗
=
|
g
/
ρ
0
Π
|
. The conditionally averaged profiles of potential enstrophy
Π
2
, enstrophy
ω
2
, and turbulent kinetic energy dissipation
ε
of the two distinctly different turbulence forcing cases collapsed when scaled by
η
Π
at different time instants in each simulation. This implies not only the self-similarity of the small scale statistics of the TNTI in either of the two cases, but also the similarity between the statistics of the two different turbulent flows in the proximity of TNTI.
Re
λ
=
35
,
44
. We focus on the similarities and differences of the properties of stratified TNTIs due to two distinct types of forcing: (a) convection due to a boundary heat source and (b) agitation resembling a vertically oscillating grid experiment. Similarly to other stratified flows, the small scale dynamics of the TNTI in the present DNSs differ from what would be expected in comparable yet unstratified TNTIs. The interface cannot be indeed uniquely identified by the commonly used vorticity
ω
. Instead, the potential enstrophy
Π
2
is shown to be the most appropriate marker in these flow cases. It is emphasized that the Kolmogorov lengthscale
η
K
∼
√
ν
/
ω
is not representative of the small scale dynamics of the interface. Hence, an alternative lengthscale,
η
Π
, is defined, in analogy to the Kolmogorov scale, based on the potential enstrophy,
η
Π
=
(
ν
3
/
Π
∗
)
1
/
6
, being
Π
∗
=
|
g
/
ρ
0
Π
|
. The conditionally averaged profiles of potential enstrophy
Π
2
, enstrophy
ω
2
, and turbulent kinetic energy dissipation
ε
of the two distinctly different turbulence forcing cases collapsed when scaled by
η
Π
at different time instants in each simulation. This implies not only the self-similarity of the small scale statistics of the TNTI in either of the two cases, but also the similarity between the statistics of the two different turbulent flows in the proximity of TNTI.
Date Issued
2021-11-15
Date Acceptance
2021-11-01
Citation
Physical Review Fluids, 2021, 6 (11)
ISSN
2469-990X
Publisher
American Physical Society
Journal / Book Title
Physical Review Fluids
Volume
6
Issue
11
Copyright Statement
©2021 American Physical Society
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000722245400006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Physical Sciences
Physics, Fluids & Plasmas
Physics
INTERNAL WAVES
TURBULENT ENTRAINMENT
LAYERS
VORTICES
Publication Status
Published
Article Number
ARTN 114803