Article
Mechanics
Claudine Charrondiere, Christophe Brun, Emil J. Hopfinger, Jean-Martial Cohard, Jean-Emmanuel Sicart
Summary: Recent field measurements of katabatic winds on steep alpine slopes provide valuable data for studying the development of mean flow and mixing properties. The theory shows that the mean velocity increases with downstream distance according to a certain function. The measurements also allow for the determination of bottom drag coefficients, interfacial entrainment, and ground surface heat flux.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
J. M. Duguay, P. M. Biron, R. W. J. Lacey
Summary: This study investigates the impact of density differences on the flow structure at a river confluence, confirming the presence of coherent streamwise-oriented vortices (SOVs). The SOVs are caused by the confinement of density-driven gravity currents between the converging flows. The results show that the magnitude of the density difference and the momentum ratio of the confluence greatly influence the size and coherence of the vortices, with the largest and most coherent vortices observed when the momentum of the dense channel is greater than that of the light channel.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Wu-ting Tsai, Guan-hung Lu
Summary: In this study, numerical simulations were conducted to reveal the vortical structures of Langmuir circulations (LCs) and quasi-streamwise vortices (QSVs), and their interactions. LCs manifest themselves by inducing wind-aligned streaks on the surface, while QSVs accumulate beneath the windward surface and dominate the distribution. The formation of QSVs enhances the production of streamwise enstrophy and differs from the coherent vortical structures (CVSs) in wall turbulence.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Cyril Gadal, M. J. Mercier, M. Rastello, L. Lacaze
Summary: This experiment presents an extensive investigation of particle-laden currents in sloping topographies. The study identifies three regimes based on the ratio of settling and current inertia. The velocity of the current increases with the bottom slope, while the current head remains independent of experimental parameters.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Albert Dai, Yu-Lin Huang, Ching-Sen Wu
Summary: Investigation of the collision of two counterflowing gravity currents of equal densities and heights was carried out using three-dimensional high-resolution simulations. The study provides detailed understanding of flow structures and energetics in the collision region. The collision process can be divided into three phases, with the production of turbulent kinetic energy and turbulent buoyancy flux playing a crucial role. The study complements previous experimental investigations by presenting clear information about the mean flow and turbulent flow characteristics in the collision region.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Zhong Zheng
Summary: This paper presents a theoretical model to describe one-dimensional flows in a porous layer with vertical variations, and demonstrates the influence of different parameters on the flow. Four asymptotic regimes are identified, and analytical solutions are derived for effective relative permeability curves, shedding light on the influence of various factors.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
M. Ungarish
Summary: This study revisits the theoretical solutions to the problem of reflected flow resulting from the dambreak of a Cartesian long reservoir over a dry bottom and with tailwaters. A simplified model is developed based on the assumption that the fluid between the obstacle and the reflected jump is stagnant. The model provides the position, height, and speed of the jump as functions of time and shows clear effects of the presence of tailwaters. It has been validated against exact solutions and can provide reliable insights and fast quantitative predictions for research and engineering problems.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Thomasina Ball, Neil J. Balmforth, Ariel P. Dufresne, Stephen W. Morris
Summary: When viscoplastic fluid comes into contact with water, non-axisymmetric instability occurs, resulting in the formation of flower-like patterns. This instability can be eliminated by replacing the water layer with an immiscible liquid of similar viscosity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
M. Ungarish
Summary: The study investigates the propagation of a gravity current generated from a moving source of buoyancy in deep-sea mining and related technologies. The researchers present a simple box model to gain further insights and useful analytical approximations for the flow system. The model confirms that the main governing parameter is the ratio of the speed of the source to the speed of buoyancy propagation. The study highlights the importance of the front-jump Froude number in determining the behavior of the gravity current.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Albert Dai, Yu-Lin Huang
Summary: High-resolution simulations were conducted to study the merging and splitting processes in the lobe-and-cleft structure of gravity currents on a no-slip boundary. The simulations showed that the mean lobe width and mean maximum lobe width increase with the front Reynolds number, reaching a maximum value under certain conditions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. Ungarish
Summary: Previous studies have extended Benjamin's theory for an inertial steady-state gravity current to a linearly stratified ambient. The existing closure forms do not work well for symmetric intrusions, highlighting the need for more experiments and simulations for further clarification and improvement.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Albert Dai, Yu-Lin Huang
Summary: This study focuses on the influence of relative density difference on the deceleration of gravity currents. The results indicate that the effect of relative density difference on the experimental constants and front location depends on the slope angle.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Andrew P. Grace, Marek Stastna, Kevin G. Lamb, K. Andrea Scott
Summary: The study demonstrates that the nonlinear equation of state can lead to large scale differences in the spatial and temporal evolution of freshwater gravity currents when intruding and ambient temperatures are below the temperature of maximum density. The density difference decreases at different rates depending on whether the intruding fluid temperature decreases or increases throughout the evolution of the gravity current, leading to asymmetries in head location and vertical extent of intruding fluid, with potential implications for larger scale flows in this temperature regime. These results are robust across the studied range of Grashof numbers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Oceanography
Alexandra J. Simpson, Fengyan Shi, Joseph T. Jurisa, David A. Honegger, Tian-Jian Hsu, Merrick C. Haller
Summary: Aerial images and numerical simulations show the presence of horizontal instabilities along the front of an ebbing river plume in a tidal cross-flow, confirming their existence in both observed and modeled scenarios.
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
(2022)
Article
Mechanics
Yan Liu, Thorsten Stoesser, Hongwei Fang
Summary: This study investigates the response of turbulent flow and water surface fluctuations in partially filled pipes through large eddy simulations. The results show that as the water depth increases, the strength of the main secondary flow and the magnitude of water surface fluctuations also increase. Pre-multiplied spectra provide further evidence of the origin of the surface waves. Analysis of the wavenumber-frequency spectra reveals different types of surface waves.
Article
Engineering, Civil
Hao Wu, Jie Zeng, George Constantinescu
Summary: A numerically-based approach was used to propose a modified formula for riprap size selection, taking into account the effects of bank curvature and floodplain width on apron design.
JOURNAL OF HYDRAULIC RESEARCH
(2021)
Article
Environmental Sciences
Talia Tokyay
Summary: This numerical study investigates the evolution of high density fluid introduced vertically to a rotational low-density ambient through a circular inlet on a cone, analyzing the effects of different inflow discharges, densities, and ambient rotations on the formation and evolution of the current. The study evaluates the impact of rotational ambient on the current based on effective Ekman number and Rossby analogue, and discusses the relationship between entrainment and various flow parameters, including Reynolds and Froude numbers. The study observes a Taylor-column like formation around the inlet for flows with small Rossby analogue, and finds that the combined effect of Reynolds and Froude numbers on entrainment is less noticeable for currents propagating in the rotational ambient conditions considered.
ENVIRONMENTAL FLUID MECHANICS
(2021)
Article
Mechanics
Zhengyang Cheng, George Constantinescu
Summary: When two converging flows of unequal velocities and different flow directions come into contact, large-scale coherent structures are generated, including Kelvin-Helmholtz vortices and streamwise-oriented vortical cells. The mixing layer formed in this process affects flow, turbulence structure, and sediment entrainment mechanisms.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Civil
Sara Venuleo, Dubravka Pokrajac, Talia Tokyay, George Constantinescu, Anton J. Schleiss, Mario J. Franca
Summary: Based on the results of large eddy simulation, this study investigates the sensitivity of gravity current depth results to definition, the impact of density and velocity profile nonuniformity on coefficients in depth-averaged continuity and momentum equations, and the sensitivity of entrainment coefficient to current depth definition. The study shows that different definitions of current depth can lead to significantly different numerical results, and the entrainment coefficient is more sensitive to parameterization than the definition of current depth.
JOURNAL OF HYDRAULIC ENGINEERING
(2021)
Article
Engineering, Civil
Hao Wu, Jie Zeng, George Constantinescu
Summary: The study investigates the minimum median diameter of riprap stones needed to prevent shear failure, proposes a design formula for riprap size selection, and estimates the maximum Froude number at which riprap stones can resist shear failure.
JOURNAL OF HYDRAULIC ENGINEERING
(2021)
Article
Environmental Sciences
Chenyu Jiang, George Constantinescu, Saiyu Yuan, Hongwu Tang
Summary: In this study, numerical techniques are used to investigate the flow dynamics and mixing at the asymmetric confluence between the Yangtze River and the Poyang Lake channel. The effects of density contrast between the confluent flows and its impact on the flow structure and thermal mixing are also examined. The study found that density contrast leads to lateral near-bed intrusions and strong tilting of the mixing interface boundaries, ultimately increasing mixing at large distances from the confluence apex.
ENVIRONMENTAL FLUID MECHANICS
(2023)
Article
Mechanics
Zhengyang Cheng, George Constantinescu
Summary: This study investigates the mixing process between two parallel streams of different velocities and densities. The results show that the lock-exchange-like flow plays a crucial role in mixing and sediment entrainment, especially when there is a significant density difference between the two streams.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Water Resources
Hao Wu, George Constantinescu
Summary: This study investigates the changes in flow structure, drag forces, sediment entrainment mechanisms, and dilution of filtered water jet with increasing angle of attack for freshwater mussels in rivers. The results show that increasing angle of attack leads to greater drag forces on the mussel shell, stronger flow circulation, and increased shear stresses near the mussel, indicating potential for local scouring.
ADVANCES IN WATER RESOURCES
(2022)
Editorial Material
Agricultural Engineering
Seyed M. Hajimirzaie, George Constantinescu, Xiaofeng Liu, Thorsten Stoesser, Kaveh Zamani
JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING
(2022)
Article
Geosciences, Multidisciplinary
A. N. Sukhodolov, O. O. Shumilova, G. S. Constantinescu, Q. W. Lewis, B. L. Rhoads
Summary: This article introduces a theory for the mixing dynamics of shallow flows at confluences, and verifies the theoretical predictions and transitional behavior between two mixing modes through dye visualizations in field experiments. According to the theoretical framework, the mixing interface can grow rapidly in one mode, even though flow curvature and shallowness restrict growth through advective and turbulent lateral exchange of momentum and bed friction. These findings provide insight into the importance of different flow structure modalities in controlling mixing at river confluences and contribute to understanding the role of confluences in contaminant dispersion in river systems.
Article
Mechanics
Wen-Yi Chang, George Constantinescu
Summary: In this study, flow and turbulent structures generated by the interaction of forced incoming oscillatory flow with a circular, vertical cylinder are investigated using eddy-resolving simulations. The results show that detached eddy simulation (DES) predicts more accurately the amplification of the bed shear stress and the maximum magnitude of the bed shear stress compared with unsteady Reynolds-averaged Navier-Stokes simulations. High-Reynolds-number DES simulations reveal the changes in the wake vortex-flow regimes and the generation of other near-bed coherent structures in the wake during the oscillatory cycle.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Environmental Sciences
T. Lazzarin, G. Constantinescu, L. Di Micco, H. Wu, F. Lavignani, M. Lo Brutto, D. Termini, D. P. Viero
Summary: The present study investigates the impact of bed roughness on flow and turbulence structure around an isolated, partially-buried mussel. The results show that increasing bed roughness amplifies turbulence kinetic energy in the near-wake region and weakens the strength of the main downwelling flow.
WATER RESOURCES RESEARCH
(2023)
Article
Mechanics
Mete Koken, George Constantinescu
Summary: This paper discusses the influence of the submergence ratio on the flow and turbulence structure inside and around an array of solid rigid cylinders. The vertical shear layer developed between the top face of the array and the free surface significantly increases flow three-dimensionality and modifies the momentum exchange between the array and surrounding open water regions. Eddy-resolving simulations show that the flow characteristics and turbulence phenomena inside the array vary with different solid volume fractions and submergence ratios.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Geosciences, Multidisciplinary
Oleksandra O. Shumilova, Alexander N. Sukhodolov, George S. Constantinescu, Bruce J. MacVicar
Summary: This study presents a detailed dataset on the hydrodynamics of shallow wake flows behind solid and porous obstructions, collected in a field experimental campaign in a side branch of the Tagliamento River in Italy. The dataset includes 30 experimental runs and provides valuable information for studying flow dynamics, validating numerical models, and understanding the effects of driftwood accumulations on wake dynamics.
EARTH SYSTEM SCIENCE DATA
(2021)