Article
Environmental Sciences
M. Conde-Frias, M. Ghisalberti, R. J. Lowe, M. Abdolahpour, V. Etminan
Summary: This study investigates the near-bed mean and turbulent flow properties within aquatic vegetation and finds that vegetation density strongly influences the thickness of the bottom boundary layer (BBL) and bed shear stress. A model based on near-bed turbulent kinetic energy (TKE) is developed to predict the BBL thickness and bed shear stress.
WATER RESOURCES RESEARCH
(2023)
Article
Mechanics
Victor Dupuis, Frederic Y. Moulin, Olivier Eiff
Summary: The experiments were conducted in an open-channel flow with a smooth section and a section consisting of submerged or emergent cubes, resulting in a shear layer with large-scale Kelvin-Helmholtz structures. The analysis of the flow was performed using a double-averaging method, allowing for measurement of the velocity field in a large volume including the interstices between the cubes. The results showed that the loss of momentum towards the rough section had a similar magnitude to the loss through bed friction, and the lateral momentum flux was mainly caused by turbulent shear stress.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Civil
Xiang Wang, Carlo Gualtieri, Wenxin Huai
Summary: The impact of aquatic vegetation on weak bed-load transport rates in riverbeds was investigated through laboratory experiments. It was observed that the transport rate increased with an increase in energy slope and a decrease in vegetation density. The traditional method of calculating bed shear stress was unable to predict the measured transport rate, but a new method considering grain shear stress provided a reasonable prediction. The proposed models were found to be more accurate than existing literature models, improving understanding of bed-load transport in vegetated flows.
JOURNAL OF HYDROLOGY
(2023)
Article
Thermodynamics
Edgar M. Ofuchi, Henrique Stel, Ernesto Mancilla, Rigoberto E. M. Morales
Summary: This study aims to investigate the flow field in a centrifugal rotor using two-dimensional Particle Image Velocimetry (PIV). The analysis of flow at different planes under various operating conditions revealed that the flow in the centrifugal rotor behaves according to kinematic similarity, even at part-load operation. Additionally, it was observed that the flow in the rotor channels can be considered periodic at the best efficiency point flow rate and under part-load conditions.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2023)
Article
Environmental Sciences
D. G. Gundersen, K. T. Christensen, G. Blois
Summary: This study presents an experimental protocol to quantify the interaction between structural deformation of fluvial vegetation canopies and fluid flow. High-speed particle image velocimetry data and corresponding solid displacement field were obtained using fluorescent imaging and refractive index matching. The time-resolved data enables observation of the dynamic link between a deformable object and the surrounding flow field.
WATER RESOURCES RESEARCH
(2022)
Article
Environmental Sciences
Mahboubeh Barahimi, Jueyi Sui
Summary: This study investigates the effects of submerged vegetation arrangement patterns and density on flow structure through experiments. The results show that the staggered configuration leads to intensified streamwise velocity, turbulence kinetic energy, and Reynolds shear stress compared to the square configuration. Additionally, the wake zone produced by low vegetation density is more expansive than that produced by high vegetation density.
Article
Thermodynamics
Abdullah G. Weiss, Paul J. Kristo, Juan R. Gonzalez, Mark L. Kimber
Summary: This study experimentally investigated the hydraulic single-phase mixing of three parallel rectangular channels. The results showed that multi-regime mixing demonstrated superior characteristics compared to turbulent mixing, with a more dramatic velocity decay in the inner flow and a shorter mixing length.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Biochemical Research Methods
Mathias Busek, Aleksandra Aizenshtadt, Timo Koch, Anna Frank, Ludivine Delon, Mikel Amirola Martinez, Alexey Golovin, Clotilde Dumas, Justyna Stokowiec, Stefan Gruenzner, Espen Melum, Stefan Krauss
Summary: We developed a pump-less directional flow recirculating organ-on-a-chip platform that creates controlled unidirectional gravity-driven flow. The platform features two organoid compartments supported by independent perfusion channels, separated by a hydrogel barrier. We demonstrated the suitability of the platform for functional culture of endothelial cells and the viability of human stem-cell derived liver organoids, as well as the circulation of immune cells in the microfluidic channels.
Article
Environmental Sciences
Arif Jewel, Kazunori Fujisawa, Akira Murakami
Summary: The experiment explores the incipient motion of sands on both sand and smooth beds by estimating bed shear stress through four different indirect methods. Particle image velocimetry was used to study flow dynamics and incipient motion. The critical shear velocity at incipient motion was used to evaluate Manning roughness and Darcy-Weisbach friction coefficients in both sand and smooth zones.
Article
Agricultural Engineering
Miroslav Rebej, Tomas Jurena, Jiri Vondal, David Fuente Herraiz, Jan Cerveny, Zdenek Jegla
Summary: This paper presents the use of PIV technique to measure velocity fields in a stirred photobioreactor and validate a CFD model. The study includes grid independence analysis, velocity profiles, and shear stresses for different operating conditions. The results show good correlation between the numerical model and experimental data, but uncertainties exist in PIV measurements for bubbly flows.
BIOSYSTEMS ENGINEERING
(2023)
Article
Thermodynamics
Yilin Yang, Meilan Qi, Jinzhao Li, Xiaodong Ma
Summary: The experimental study focused on the flow fields around different pile groups mounted vertically on a flat bed using Particle Image Velocimetry (PIV). It systematically investigated the characteristics of the horseshoe vortex (HV), the bed shear stress, and the flow features between the piles. The influences of pile Reynolds number (Re-D) and pile spacing (G/D) on the flow characteristics were thoroughly discussed.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2021)
Article
Engineering, Civil
Parisa Setayesh, Hossein Afzalimehr
Summary: This study experimentally investigates the distributions of velocity in 3D in gravel bed channels with vegetation and examines six different methods for estimating bed shear stress. The distribution of shear stress is mainly controlled by the spatial distribution of vegetation and the biomechanical and architectural features of these plants, leading to a layered shape of shear stress near the bottom of the flume.
IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY-TRANSACTIONS OF CIVIL ENGINEERING
(2022)
Article
Mechanics
David C. Fritts, L. Wang, S. A. Thorpe, T. S. Lund
Summary: Fritts et al. (J. Fluid Mech., vol. xx, 2022, xx) present a direct numerical simulation study of interacting Kelvin-Helmholtz instability (KHI) billows with variable initial phases. They find that tube and knot dynamics associated with KHI drive stronger and faster turbulence transitions compared to secondary instabilities of individual KH billows. The results also show higher energy dissipation rates and large-scale Kelvin 'twist waves' caused by tube and knot dynamics, leading to fragmentation of vortex tubes and billow cores. These findings contribute to a better understanding of the dynamics and energy dissipation processes in KHI.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Chemical
Tom Lacassagne, Serge Simoens, Mahmoud EL Hajem, Jean-Yves Champagne
Summary: In this study, POD was applied to investigate the flow generated by an oscillating grid in water and a shear thinning dilute polymer solution. The research revealed a dominance of low order POD modes in the polymer solution, as well as strong mode coupling in the grid swept region influenced by the working fluid and chaotic nature of the flow. The study also discussed the possibilities of reconstructing turbulence properties using high-order modes.
Article
Thermodynamics
Ben Wang, Qi Wang, Zhen-Hua Wan, De-Jun Sun
Summary: Buoyancy driven turbulence with free-slip top and bottom plates in a confined box is studied via direct numerical simulations. Hysteresis-like behavior of heat and momentum transfer is found due to the emergence of two stable states of flow organization with the variation of depth/height aspect ratio. The heat and momentum transport is greatly suppressed in the shear flow state compared with that in the convection roll state, with different dominant processes in energy transport identified in each state.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2021)