Special Issue "Boundary Layer Processes in Geophysical/Environmental Flows"

A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Geophysical and Environmental Fluid Mechanics".

Deadline for manuscript submissions: 15 February 2022.

Special Issue Editors

Prof. Dr. Joseph J. Kuehl
E-Mail Website
Guest Editor
Mechanical Engineering Department, University of Delaware, Newark, DE 19716, USA
Interests: geophysical/environmental fluid dynamics; hypersonic flow; boundary layer stability; transition to turbulence; time-series analysis
Dr. Pengfei Xue
E-Mail Website
Guest Editor
Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, MI 49931, USA
Interests: hydrodynamic modeling; regional climate modeling; coupled ocean/lake-atmosphere modeling and dynamics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Fabrice Veron
E-Mail Website1 Website2
Guest Editor
School of Marine Science and Policy, University of Delaware, Newark, DE 19716, USA
Interests: air-sea interactions; wave breaking; airflow over waves; sea spray

Special Issue Information

Dear Colleagues,

Boundary layer processes play a crucial role in establishing circulation patterns of the oceans and atmosphere, significantly affecting both regional climates and the global climate, as well as the distributions of heat, nutrients, species, pollutants, and more. This Special Issue of Fluids is dedicated to recent advances in the theoretical, numerical, observational (including instrumentation development), and experimental investigation of geophysical/environmental boundary layer processes and how those process may influence regional and global circulation.  Topics of interest include, but are not limited to, air–sea interactions and fluxes (including the influence of sea-ice), western and eastern boundary currents, bottom boundary processes (including complex topography interactions, sediment motion), and internal boundary layers (such as fronts, shear layers, and thermocline processes).

Prof. Dr. Joseph J. Kuehl
Dr. PengFei Xue
Dr. Fabrice Veron
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • air–sea interactions
  • western/eastern boundary currents
  • bottom boundary layer processes
  • sea-ice cover
  • air–sea flux
  • layered/stratified systems
  • fluid stability

Published Papers (4 papers)

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Research

Article
The Impacts of Gustiness on Air–Sea Momentum Flux
Fluids 2021, 6(10), 336; https://doi.org/10.3390/fluids6100336 - 22 Sep 2021
Viewed by 273
Abstract
The exchange of momentum across the air–sea boundary is an integral component of the earth system and its parametrization is essential for climate and weather models. This study focuses on the impact of gustiness on the momentum flux using three months of direct [...] Read more.
The exchange of momentum across the air–sea boundary is an integral component of the earth system and its parametrization is essential for climate and weather models. This study focuses on the impact of gustiness on the momentum flux using three months of direct flux observations from a moored surface buoy. Gustiness, which quantifies the fluctuations of wind speed and direction, is shown to impact air–sea momentum fluxes. First, we put forward a new gustiness formula that simultaneously evaluates the impact of fluctuations in wind direction and speed. A critical threshold is established using a cumulative density function to classify runs as either gusty or non-gusty. We find that, during runs classified as gusty, the aerodynamic drag coefficient is increased up to 57% when compared to their non-gusty counterparts. This is caused by a correlated increase in vertical fluctuations during gusty conditions and explains variability in the drag coefficient for wind speeds up to 20 m/s. This increase in energy is connected with horizontal fluctuations through turbulent interactions between peaks in the turbulent spectra coincident with peaks in the wave spectra. We discus two potential mechanistic explanations. The results of this study will help improve the representation of gustiness in momentum flux parameterizations leading to more accurate ocean models. Full article
(This article belongs to the Special Issue Boundary Layer Processes in Geophysical/Environmental Flows)
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Article
Moored Flux and Dissipation Estimates from the Northern Deepwater Gulf of Mexico
Fluids 2021, 6(7), 237; https://doi.org/10.3390/fluids6070237 - 30 Jun 2021
Viewed by 451
Abstract
Results from a pilot program to assess boundary mixing processes along the northern continental slope of the Gulf of Mexico are presented. We report a novel attempt to utilize a turbulence flux sensor on a conventional mooring. These data document many of the [...] Read more.
Results from a pilot program to assess boundary mixing processes along the northern continental slope of the Gulf of Mexico are presented. We report a novel attempt to utilize a turbulence flux sensor on a conventional mooring. These data document many of the features expected of a stratified Ekman layer: a buoyancy anomaly over a height less than that of the unstratified Ekman layer and an enhanced turning of the velocity vector with depth. Turbulent stress estimates have an appropriate magnitude and are aligned with the near-bottom velocity vector. However, the Ekman layer is time dependent on inertial-diurnal time scales. Cross slope momentum and temperature fluxes have significant contributions from this frequency band. Collocated turbulent kinetic energy dissipation and temperature variance dissipation estimates imply a dissipation ratio of 0.14 that is not sensibly different from canonical values for shear instability (0.2). This mixing signature is associated with production in the internal wave band rather than frequencies associated with turbulent shear production. Our results reveal that the expectation of a quasi-stationary response to quasi-stationary forcing in the guise of eddy variability is naive and a boundary layer structure that does not support recent theoretical assumptions concerning one-dimensional models of boundary mixing. Full article
(This article belongs to the Special Issue Boundary Layer Processes in Geophysical/Environmental Flows)
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Article
Direct Numerical Simulation of Sediment Transport in Turbulent Open Channel Flow Using the Lattice Boltzmann Method
Fluids 2021, 6(6), 217; https://doi.org/10.3390/fluids6060217 - 09 Jun 2021
Cited by 1 | Viewed by 906
Abstract
The lattice Boltzmann method is employed to conduct direct numerical simulations of turbulent open channel flows with the presence of finite-size spherical sediment particles. The uniform particles have a diameter of approximately 18 wall units and a density of [...] Read more.
The lattice Boltzmann method is employed to conduct direct numerical simulations of turbulent open channel flows with the presence of finite-size spherical sediment particles. The uniform particles have a diameter of approximately 18 wall units and a density of ρp=2.65ρf, where ρp and ρf are the particle and fluid densities, respectively. Three low particle volume fractions ϕ=0.11%, 0.22%, and 0.44% are used to investigate the particle-turbulence interactions. Simulation results indicate that particles are found to result in a more isotropic distribution of fluid turbulent kinetic energy (TKE) among different velocity components, and a more homogeneous distribution of the fluid TKE in the wall-normal direction. Particles tend to accumulate in the near-wall region due to the settling effect and they preferentially reside in low-speed streaks. The vertical particle volume fraction profiles are self-similar when normalized by the total particle volume fractions. Moreover, several typical transport modes of the sediment particles, such as resuspension, saltation, and rolling, are captured by tracking the trajectories of particles. Finally, the vertical profiles of particle concentration are shown to be consistent with a kinetic model. Full article
(This article belongs to the Special Issue Boundary Layer Processes in Geophysical/Environmental Flows)
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Article
Flow Past Mound-Bearing Impact Craters: An Experimental Study
Fluids 2021, 6(6), 216; https://doi.org/10.3390/fluids6060216 - 09 Jun 2021
Viewed by 579
Abstract
An experimental investigation into the flow produced by mound-bearing impact craters is reported herein. Both an idealized crater and a scaled model of a real martian crater are examined. Measurements were performed using high-resolution planar particle image velocimetry (PIV) in a refractive-index matching [...] Read more.
An experimental investigation into the flow produced by mound-bearing impact craters is reported herein. Both an idealized crater and a scaled model of a real martian crater are examined. Measurements were performed using high-resolution planar particle image velocimetry (PIV) in a refractive-index matching (RIM) flow environment. Rendering the crater models optically invisible with this RIM approach provided unimpeded access to the flow around and within each crater model. Results showed that the mean flow within the idealized crater exhibits more structural complexity compared to its moundless counterpart. Second-order statistics highlighted regions of minimal and elevated turbulent stresses, the latter of which revealed a complex interaction between shear layers that are present at the upstream and downstream parts of the rim and the central mound. Periodic vortex shedding of quasi-spanwise vortices from the upstream rim was revealed by POD-filtered instantaneous flow fields. Vertical flapping of this shear layer resulted in vortices occasionally impinging on the inner wall of the downstream rim. Further, conditional averaging analysis suggested periodic lateral oscillations of wall-normal vortices within the crater rim region reminiscent of those observed for flow inside spherical dimples. These results have implications for intra- to extra-crater mass and momentum exchange, and for sediment transport processes. Lastly, experiments with the Gale Crater model showed both similarities with and differences from the primary flow features found for the idealized model. Full article
(This article belongs to the Special Issue Boundary Layer Processes in Geophysical/Environmental Flows)
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