Article
Mechanics
G. D. Portwood, S. M. de Bruyn Kops, C. P. Caulfield
Summary: This study investigates the impact of turbulent dynamic range on active scalar mixing in stably stratified turbulence and proposes a model framework for irreversible diapycnal mixing under high Reynolds number conditions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Geosciences, Multidisciplinary
Junbiao Tu, Daidu Fan, Zhiyu Liu, William Smyth
Summary: This study obtained estimates of the flux Richardson number R-f in a strongly turbulent, sediment-stratified estuarine flow. The parameterization based on the turbulent Froude number Fr-t was found to be the most effective.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Mechanics
Young R. Yi, Jeffrey R. Koseff
Summary: In this study, we revisit and extend the turbulent Froude number scaling for the mixing coefficient by incorporating the effects of mean shear. Through the use of different datasets and simulations, we propose a revised scaling that better applies to vertically sheared turbulence with stable stratification, while also considering additional effects such as radiative heating/cooling and changes in shear direction.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Vassili Issaev, N. Williamson, S. W. Armfield, S. E. Norris
Summary: This study investigates the dynamics and parameterization of mixing in temporally evolving turbulent open-channel flow through direct numerical simulations. Three different mixing regimes are observed and the relationship between the mixing coefficient, flux Richardson number, and the gradient Richardson number is analyzed. Scaling relationships between Ri(g) and Fr are derived, and differences in the scaling of L-E/L-O with Fr-1 in the intermediate regime are discussed.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jin-Han Xie, Shi-Di Huang
Summary: Through simulations of an idealized isotropic convection system, we provide evidence for the existence of Bolgiano-Obukhov (BO) scaling in Rayleigh-Benard convection (RBC) and establish its association with the inverse kinetic energy cascade. We also observe strong intermittent effects in the buoyancy field, but not in the velocity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ali Akhavan-Safaei, Mohsen Zayernouri
Summary: In this study, the spectral transfer model for turbulent intensity in passive scalar transport is reconsidered and a modification to the scaling of scalar variance cascade is proposed. A revised scalar transport model is obtained based on the modified spectral transfer model, using a fractional-order Laplacian operator to include the non-local effects from large-scale anisotropy in the turbulent cascade. The developed model is analyzed through numerical simulation, comparing it with the standard version in terms of scalar variance, scalar gradient statistics, and two-point statistical metrics of turbulent transport.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
H. Lam, A. Delache, F. S. Godeferd
Summary: The study focuses on the strong stratification regime of stably stratified turbulence and the viscosity-affected stratified state, decomposing the three-dimensional velocity-density fields into internal gravity waves (IGWs) and eddy motion. Separate evolution equations for IGWs and eddies are established. At Re-b around 1, a significant exchange of energy from IGWs to eddies is observed, while for Re-b > 1, the dynamics of IGWs and eddies appear to be separate with no global energy exchange. The mixing due to eddies is found to be four times greater than that due to waves at the largest Re-b considered.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Valentin A. Skoutnev
Summary: We extend the scaling relations of strongly (stably) stratified turbulence from the geophysical regime of unity Prandtl number to the astrophysical regime of extremely small Prandtl number applicable to stably stratified regions of stars and gas giants. A transition to a new turbulent regime is found to occur when the Prandtl number drops below the inverse of the buoyancy Reynolds number, i.e. Pr Rb < 1, which signals a shift of the dominant balance in the buoyancy equation. Application of critical balance arguments then derives new predictions for the anisotropic energy spectrum and dominant balance of the Boussinesq equations in the Pr Rb << 1 regime.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Vassili Issaev, N. Williamson, S. W. Armfield
Summary: Through numerical simulations, we investigate the effects of spatiotemporal intermittency in surface heated stratified open channel flow. We demonstrate that the flow can be divided into regions of active turbulence and surrounding quiescent fluid, with the intermittency manifested as a deformed horizontal interface between the two. The vertical intermittency profile is accurately predicted by a normalized local Monin-Obukhov length.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Ricardo P. Xavier, Miguel A. C. Teixeira, Carlos B. da Silva
Summary: This study investigates the characteristics of velocity fluctuations in turbulent flows using theoretical analysis and numerical simulations, revealing the asymptotic laws for variance of velocity fluctuations, Taylor micro-scale, and viscous dissipation rate at different distances from turbulent/non-turbulent interface. The results are confirmed to be independent of Reynolds number and applicable to other flow configurations with appropriate kinetic energy spectra.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Environmental Sciences
Annick Pouquet, Duane Rosenberg, Raffaele Marino, Pablo Mininni
Summary: This article analyzes the results of direct numerical simulations of rotating stratified flows and discovers intermittent fluctuations and their relations with buoyancy flux and energy dissipation. These findings are similar to those in other fields.
Article
Mechanics
Christopher J. Howland, John R. Taylor, C. P. Caulfield
Summary: This study discusses the significant influence of turbulent mixing on physical processes in the ocean and proposes a new technique to calculate APE in periodic domains with a mean stratification. The results show that the mean dissipation rate of buoyancy variance provides a good approximation to the mean diapycnal mixing rate, but there is significant variation in quantifying mixing efficiency depending on whether laminar diffusion of a mean flow is included. The study explores how best to interpret these results in the context of quantifying diapycnal diffusivity in real oceanographic flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Miles M. P. Couchman, Stephen M. de Bruyn Kops, Colm-cille P. Caulfield
Summary: Understanding the role of stable density interfaces in turbulent mixing in density-stratified fluids is crucial in geophysical fluid dynamics. By analyzing the correlations between the vertical density gradient ??/?z, the dissipation rates of kinetic energy e, and the scalar variance ? in a single forced direct numerical simulation of stratified turbulence, we find that significant mixing occurs in anisotropic statically stable regions of the flow. Our findings suggest that current parametrizations of turbulent mixing may be biased by undersampling and that further investigation into the role of stable density interfaces is needed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Chemical
Maathangi Ganesh, Sadegh Dabiri
Summary: Direct numerical simulations were conducted to analyze the dynamics and destratification effects of a large number of bubbles rising in unbounded stratified fluids. The influence of bubble deformability and Reynolds numbers on background mixing was investigated, revealing that highly deformable, high Reynolds number bubbles enhance mixing. The study also examined the influence of bubble motion on liquid and bubble velocity fluctuations, as well as turbulent kinetic energy levels. The results demonstrated an increase in buoyancy flux and vertical mass flux as void fraction and stratification strength varied.
CHEMICAL ENGINEERING SCIENCE
(2022)
Article
Mechanics
Wen Zhang, Xiaowei Zhu, Xiang I. A. Yang, Minping Wan
Summary: The mixing-layer analogy is an important tool in studying vegetation canopy flow, but it has received limited support in urban-canopy flow research. This study revisits the mixing-layer analogy and presents evidence for its applicability in urban-canopy flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Ocean
Rodolfo T. Goncalves, Nicole H. Hannes, Maria E. F. Chame, Pedro P. S. P. Lopes, Shinichiro Hirabayashi, Hideyuki Suzuki
APPLIED OCEAN RESEARCH
(2020)
Article
Engineering, Civil
Rodolfo Trentin Goncalves, Maria Eduarda Felippe Chame, Nicole Hepp Hannes, Pedro Paludetto Silva de Paula Lopes, Shinichiro Hirabayashi, Hideyuki Suzuki
INTERNATIONAL JOURNAL OF OFFSHORE AND POLAR ENGINEERING
(2020)
Article
Engineering, Marine
Valerio Bianchi, Leandro S. P. Silva, Fredi Cenci, Shinichiro Hirabayashi, Hideyuki Suzuki, Rodolfo T. Goncalves
Article
Thermodynamics
Pei-Ying Hsieh, Wu-Yang Sean, Toru Sato, Yong-Won Seo
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2020)
Article
Engineering, Marine
Hideyuki Suzuki, Hiroki Shiohara, Anja Schnepf, Hidetaka Houtani, Lucas H. S. Carmo, Shinichiro Hirabayashi, Ken Haneda, Toshiki Chujo, Yasunori Nihei, Edgard B. Malta, Rodolfo T. Goncalves
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2020)
Article
Computer Science, Interdisciplinary Applications
Shunsuke Kanao, Toru Sato
Summary: A numerical method called the adjoint marginal sensitivity method was proposed to estimate leakage positions and fluxes of pollutants in the ocean. The study improved the method to handle multiple leakage positions and demonstrated the conditions for successful estimation through simulation results, also applying the method to a three-dimensional case.
COMPUTERS & FLUIDS
(2022)
Article
Green & Sustainable Science & Technology
Shuxuan Sun, Toru Sato, Keisuke Uchimoto, Yuji Watanabe
Summary: The method of using multiple indicators to monitor CO2 concentrations in seawater has been proposed to avoid false positives. Through studying seawater samples worldwide, it was found that world seawaters can be classified into three groups and at least one indicator has a clear correlation with CO2 concentrations in each group, demonstrating the effectiveness of the proposed method.
INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL
(2021)
Article
Green & Sustainable Science & Technology
Yosuke Sawano, Takuya Wako, Toru Sato, Kazuhiro Tada
Summary: CO2 capture and storage is a promising strategy to combat global warming. CO2 hydrate formation can help suppress CO2 leakage, with the sealing effect depending on the absolute permeability of the storage site.
INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL
(2022)
Article
Energy & Fuels
Alan Junji Yamaguchi, Toru Sato, Takaomi Tobase, Xinran Wei, Lin Huang, Jia Zhang, Jiang Bian, Tie-Yan Liu
Summary: This study proposes a novel multiscale numerical method to estimate the permeability of hydrate-bearing sediments in reservoir-scale simulations based on machine learning techniques. The proposed method was validated by comparing the results with existing mathematical permeability models, showing similar hydrate distribution but slight differences in permeability values. This method demonstrates its uniqueness in capturing the spatial distribution of permeability values.
Article
Green & Sustainable Science & Technology
Shuyan Lu, Alan Junji Yamaguchi, Kaito Kobayashi, Toru Sato, Takaomi Tobase
Summary: This study provides a numerical simulation method for CO2 hydrate formation in microscopic porous media with consideration of two-phase flow. The influence of hydrate formation rate and flow speed on permeability reduction was studied. Results showed that the ratio of flow speed to hydrate formation rate affects permeability reduction.
INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL
(2022)
Article
Engineering, Marine
Jiayue Hui, Toru Sato, Shunsuke Kanao
Summary: Marine plastic is a global problem, especially in the Sea of Japan. Tsushima Island and other beaches in the region face serious issues with beach plastics. The cost of beach cleanup is high, so identifying and recovering large floating plastic hotspots offshore may be a more economical option. This study used numerical methods and measurement data to estimate the hotspot position of floating plastic bags in the Tsushima Strait, and the results were comparable to satellite images.
Article
Energy & Fuels
Hiroyuki Oyama, Wenxiang Ye, Tsuyoshi Shimojo, Yosuke Sawano, Toru Sato, Norio Tenma
Summary: The tensile response of methane hydrate (MH) without sand particles was studied, and the parameters for a discrete element method (DEM) were extracted. The study found that the tensile Young's modulus of MH ranged from 6 to 48 MPa, and its tensile strength ranged from 0.14 to 1.14 MPa, with higher filling ratios resulting in higher tensile strength.
Article
Engineering, Ocean
Hiroyuki Oyama, Tomoya Ogino, Toru Sato, Hisato Yasuda, Jiro Nagao, Norio Tenma
Summary: It has been discovered that mud flocs and methane hydrate coexist in sediment layers off the coast of Japan. There is concern that the flow of pure water from the dissociation of methane hydrate may break down the mud flocs, leading to sand problems in production wells. This study examined the characteristics of the flocs by observing samples collected from natural cores and testing their mechanical stability in distilled water flow. The flocs were found to mainly consist of silt and were stable under certain flow rates, but decomposed into silt and clay particles when subjected to pressure, suggesting they could be a source of fine particles as underground stress conditions change.
MARINE GEORESOURCES & GEOTECHNOLOGY
(2023)
Article
Green & Sustainable Science & Technology
Shunsuke Nishimura, Shuxuan Sun, Toru Sato, Hiroyuki Oyama, Keisuke Uchimoto, Koichi Goto, Meguru Miki
INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL
(2020)
Article
Green & Sustainable Science & Technology
Tatsuya Fuji, Kentaro Kamada, Toru Sato, Hiroyuki Oyama, Alan Junji Yamaguchi, Takaomi Tobase
INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL
(2020)