Article
Oceanography
David James Cannon, Cary Troy, Harvey Bootsma, Qian Liao, Rae-Ann MacLellan-Hurd
Summary: This study reports on turbulent mixing observed during the annual stratification cycle in the hypolimnetic waters of Lake Michigan, highlighting stratified, convective, and transitional mixing periods. Results show a shallow, wind-driven surface mixed layer and locally elevated dissipation rates in the thermocline during the stratified summer, while turbulence is weak and buoyancy-suppressed below the thermocline.
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
(2021)
Article
Mechanics
Ian P. Castro, J. W. Kim, A. Stroh, H. C. Lim
Summary: This study presents data from numerical simulations of channel flow with surface-mounted rectangular ribs, showing the effects of secondary flows induced by the ribs. It is found that the direction of secondary flows is largely independent of rib spacing, while the strength of secondary flows depends on the ratio of rib spacing to rib width and Reynolds number. The topological features of the secondary flow structure and its impact on the flow are also investigated.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Geosciences, Multidisciplinary
Maria Krutova, Mostafa Bakhoday-Paskyabi, Joachim Reuder, Finn Gunnar Nielsen
Summary: Large-eddy simulation (LES) is used to resolve large-scale turbulence and parametrize small-scale turbulence. In wind turbine wakes, resolving micro-scale turbulence requires small grid spacing and a large domain. Nesting interface effectively decreases computational time, but introduces another source of uncertainty. This study verifies the nesting effects on shear-driven flow in LES using the PALM model system.
GEOSCIENTIFIC MODEL DEVELOPMENT
(2023)
Article
Mechanics
Mitchell Fowler, Tamer A. Zaki, Charles Meneveau
Summary: A large eddy simulation wall model is developed based on a formal interpretation of quasi-equilibrium that governs momentum balance. The model includes a relaxation time scale that ensures self-consistency with assumed quasi-equilibrium conditions. The new approach allows for formally distinguishing between quasi-equilibrium and additional, non-equilibrium contributions to wall stress.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Mark W. McCorquodale, R. J. Munro
Summary: The experimental study investigates the interaction of zero-mean-shear turbulence with solid and permeable boundaries. It examines the influence of wall permeability on turbulent energy transfer and intercomponent energy transfer, showing that the mechanisms are inhibited as the permeability Reynolds number increases.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Geosciences, Multidisciplinary
Karl Lapo, Anita Freundorfer, Antonia Fritz, Johann Schneider, Johannes Olesch, Wolfgang Babel, Christoph K. Thomas
Summary: This paper presents the Large eddy Observatory, Voitsumra Experiment 2019 (LOVE19) which provides detailed observations of the weak-wind stable boundary layer (wwSBL) using distributed sensing and flight observations. It demonstrates the unique capabilities of LOVE19 data for studying boundary layer processes.
EARTH SYSTEM SCIENCE DATA
(2022)
Article
Mechanics
C. Chan, R. C. Chin
Summary: The study reveals that MVGs can create high-speed and low-speed regions through PVPs in a turbulent boundary layer, with varying skin friction in different areas. In addition, pre-processed energy spectra analysis shows that the velocity fluctuations induced by MVGs are mainly influenced by large-scale modes that span wavelengths and MVG lengths, but the energy peak eventually repositions to the near-wall streak scale in the streamwise direction.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Sergio Pirozzoli
Summary: In this study, direct numerical simulations (DNS) of the Navier-Stokes equations were used to investigate the statistics of passive scalars in turbulent flow within a smooth straight pipe. The results showed that the organization of passive scalars was similar to the axial velocity field at moderate Prandtl numbers, but impaired at low and high Prandtl numbers. The mean scalar profiles exhibited logarithmic overlap layers and universal parabolic distributions in the core part of the flow at particular Prandtl numbers. Accurate predictive formulas for the mean scalar profiles were derived using the nearly universal eddy diffusivity.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Mitchell Fowler, Tamer A. Zaki, Charles Meneveau
Summary: The recent LaRTE approach is a wall model for large-eddy simulations (LES) that separates equilibrium and non-equilibrium wall-stress dynamics. The model shows good agreement with various non-equilibrium channel flows and provides insights into wall-stress physics.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Joan Gomez, Huidan Yu, Yiannis Andreopoulos
Summary: The primary focus of this experimental work is the instability and transition to turbulence in pulsatile flows, which involve reverse flows and unsteady flow separations. By conducting experiments with different Reynolds and Womersley numbers, it was found that transition to turbulence is a spontaneous event covering the whole near-wall region.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Pierre Ricco, Martin Skote
Summary: The study shows that the Fukagata et al.’s identity simplifies to the von Kaman momentum integral equation for free-stream boundary layers. It is found that the influence of Reynolds stresses on wall-shear stress cannot be quantified for free-stream boundary layers. Analogous identities are found for channel flows, where the laminar and turbulent contributions to the skin-friction coefficient are distinguished. The study also decomposes the skin-friction coefficient into integral thicknesses to quantify the contributions of different terms of the streamwise momentum equation to friction drag.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Naveen N. N. Kethavath, Kingshuk Mondal, Niranjan S. S. Ghaisas
Summary: This study investigates the evolution of a wind turbine wake downstream of an abrupt change in surface roughness. The results show that the changed surface roughness affects turbulent statistics such as streamwise velocity, turbulence intensity, and shear stress.
Article
Mechanics
Toni Dokoza, Martin Oberlack
Summary: In direct numerical simulations (DNS) of turbulent Couette flow, it has been observed that the length of long streamwise rolls increases with the Reynolds number. To understand this phenomenon, both linear stability theory and resolvent analysis are employed under the high Reynolds number (Re ≥ 8) and small streamwise wavenumbers (a ≥ 0) limit. The study reveals that the streamwise wavenumber of the structures needs to decrease to obtain constant streamwise structures with increasing Reynolds numbers, confirming the observations from DNS studies.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Shang-Gui Cai, Pierre Sagaut
Summary: Algebraic explicit wall models are proposed to cover the entire inner region of the turbulent boundary layer, reducing the computational effort for large eddy simulation of wall-bounded turbulent flows. The models use closed-form formulas with logarithmic- or power-function-based laws of the wall to straightforwardly evaluate the friction velocity on near wall grids, demonstrating good performance in wall modeled large eddy simulation of turbulent plane channel flow.
Article
Mechanics
Roshan Samuel, Ravi Samtaney, Mahendra K. Verma
Summary: In this study, we used a stretched spiral vortex sub-grid model to conduct large-eddy simulation of turbulent convection at extreme Rayleigh numbers. The results showed good agreement with direct numerical simulation and provided scaling relations for Nusselt and Reynolds numbers. Additionally, simulations of convection with periodic side walls revealed corresponding scaling exponents. This LES model is a promising tool for studying thermal convection at extreme Rayleigh numbers.
Article
Geosciences, Multidisciplinary
D. J. Cannon, C. D. Troy, Q. Liao, H. A. Bootsma
GEOPHYSICAL RESEARCH LETTERS
(2019)
Article
Ecology
David Cannon, Kelly Kibler, Melinda Donnelly, Giovanna McClenachan, Linda Walters, Annie Roddenberry, Jessica Phagan
ECOLOGICAL ENGINEERING
(2020)
Article
Oceanography
David James Cannon, Cary Troy, Harvey Bootsma, Qian Liao, Rae-Ann MacLellan-Hurd
Summary: This study reports on turbulent mixing observed during the annual stratification cycle in the hypolimnetic waters of Lake Michigan, highlighting stratified, convective, and transitional mixing periods. Results show a shallow, wind-driven surface mixed layer and locally elevated dissipation rates in the thermocline during the stratified summer, while turbulence is weak and buoyancy-suppressed below the thermocline.
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
(2021)
Article
Oceanography
David Cannon, Ayumi Fujisaki-Manome, Jia Wang, James Kessler, Philip Chu
Summary: The largest lakes in the world, including the Laurentian Great Lakes, have undergone significant surface warming and loss of ice cover in recent decades. However, the changes below the surface have not been extensively studied, despite their importance for various ecological processes. This study investigates the subsurface thermal structure and timing in Lake Michigan-Huron in relation to climate warming. The results show significant changes in ice cover, ice thickness, surface temperature, and bottom temperature over the past 40 years, especially in ecologically important bays. The study also highlights the shifting stratification dynamics and its impact on the overturning behavior and timing in the lake.
Article
Ecology
David J. Cannon, Kelly M. Kibler, Jyotismita Taye, Stephen C. Medeiros
Summary: The structural complexity of oyster reef canopy is important in promoting biodiversity, balancing sediment budget, and modulating hydrodynamics in estuarine systems. This study used a novel laser-scan approach to measure the surface of intact and restored reefs, providing estimates of hydrodynamically relevant roughness characteristics. The results provide spatially explicit surface roughness characterizations for healthy oyster reefs, which have applications in restoration science and nature-based feature design.
RESTORATION ECOLOGY
(2023)