Article
Mechanics
Anatoliy Lebedev, Konstantin Dobroselsky, Alexey Safonov, Sergey Starinskiy, Veronica Sulyaeva, Aleksei Lobasov, Vladimir Dulin, Christos N. Markides
Summary: The study demonstrates that sectoral coating with a hydrophobic fluoropolymer is an effective method for controlling flow separation and turbulent wake behind a cylinder in high Reynolds number flows. Time-resolved particle image velocimetry measurements show that the shape of the wake and trajectory of large-scale vortex structures are influenced by delayed flow separation on one side of the cylinder due to micro-bubbles traveling along the coated surface.
Article
Physics, Fluids & Plasmas
Noura Bettaieb, Marco Castagna, Pierre-Yves Passaggia, Azeddine Kourta, Nicolas Mazellier
Summary: In this study, a mechanism is proposed to explain the loss of performance of superhydrophobic (SH) surfaces in laminar flow regimes, considering the flow of air inside the plastron and the associated momentum loss induced by roughness elements with different geometric characteristics. Numerical simulations and experiments show that high roughness and low porosity lead to a loss of drag reduction.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Nanoscience & Nanotechnology
Bin Liu, Yongming Zhang
Summary: This study investigates the natural transition in flat-plate boundary layers on superhydrophobic surfaces, considering the influence of the leading edge region. A computational method is proposed to accurately obtain the flow field from the leading edge region to the downstream region, taking into account the influence of the leading edge region. The results show that the leading edge region decreases the thickness of the laminar boundary layers and increases the slip velocity on the wall. The influence of the leading edge region also delays the critical location of flow instability and narrows the unstable zone. Additionally, a method for predicting the spectrum of wall fluctuating pressure in the laminar flow region over underwater vehicles is presented.
Article
Chemistry, Multidisciplinary
Lorenzo Cacciatori, Carlo Brignoli, Benedetto Mele, Federica Gattere, Celeste Monti, Maurizio Quadrio
Summary: This study assesses for the first time the effects of riblets on the total aerodynamic drag of a low-speed UAV using RANS simulations. The results show that installing riblets with optimal size can significantly reduce the drag coefficient of the aircraft, and installing riblets on the wing can further decrease the drag, improving the cost-benefit ratio.
APPLIED SCIENCES-BASEL
(2022)
Article
Chemistry, Multidisciplinary
Hamed Esmaeilzadeh, Keqin Zheng, Carol Barry, Joey Mead, Majid Charmchi, Hongwei Sun
Summary: This study evaluated the performance of hydrophobic surfaces under external hydrostatic pressures using an acoustic wave device (QCM), finding that the wetting state of hydrophobic surfaces transitions at a critical hydrostatic pressure and the drag reduction induced by the surfaces decreases with increasing pressure.
Article
Engineering, Chemical
Li Wang, Longxuan Yan, Yang Liu, Zhenghao Liu, Shixing Chen, Lanjie Niu, Bingheng Lu
Summary: Superhydrophobicity is commonly used to reduce drag in pipeline transportation and prevent metal corrosion. Interfacial slip is the main factor contributing to hydrophobic surface drag reduction. Investigating the impact of wetting state on interfacial slip is crucial, and this study used an electric field to control the wetting state. Microchannel and micro-particle image velocimetry technologies were employed to examine the effect of different wetting states on interfacial slip characteristics and understand the underlying mechanism. Transitioning from the Cassie contact state to the Wenzel contact state resulted in a downward movement of the gas-liquid contact interface and weakened interface slip. Achieving the Wenzel contact state by filling the liquid to the bottom of the structure eliminated the gas-liquid interface and interface slip, leading to the loss of drag reduction effect for the hydrophobic surface.
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
(2023)
Article
Mechanics
Hae Nyeok Kim, Seung Joong Kim, Woorak Choi, Hyung Jin Sung, Sang Joon Lee
Summary: This study experimentally investigated the shear flow-induced depletion of lubricant impregnated in a single cavity, revealing that a large-scale vortex near the lubricant meniscus dramatically slows down the depletion rate. It was also found that in biomimetic LIS, cavities with smaller opening ratio have better sustainability and less lubricant depletion. These findings provide valuable insights for the design of a robust LIS system for effective and sustainable drag reduction.
Article
Engineering, Mechanical
Chao Wang, Yan Lu, Donghui Feng, Jiayuan Zhou, Yangfan Li, Hao Zhang
Summary: Through molecular dynamics simulation and experiments, the generation and slip phenomena of nanobubbles on graphene surface were studied, and the relationship between nanobubble distribution morphology and slip length was investigated.
TRIBOLOGY INTERNATIONAL
(2023)
Article
Thermodynamics
Cheng Peng, Xianpin Meng, Jian Deng, Jiang Wu
Summary: In this study, the drag reduction influenced by film boiling heat transfer on a spherical body is theoretically modeled and a semi-empirical model of drag coefficient is obtained. Verifications against experiments and classical correlations ensure the accuracy of the model. The study is important for solving drag reduction issues in FCI or thermal management and providing new understanding of mass, momentum, and heat transfer under multi-phase flow conditions.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(2022)
Article
Mechanics
Qian Mao, Jiazhen Zhao, Yingzheng Liu, Hyung Jin Sung
Summary: This study investigates the hydrodynamic mechanism of drag reduction by a flexible hairy coating through simulations and experimental data comparison, revealing the importance of flexible hairy coatings in drag reduction and the effects of different parts of the coating on drag reduction.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Mechanical
Xingwei Wang, Luyao Bao, Jun Wen, Daniele Dini, Jianbin Zhang, Li Sun, Wufang Yang, Feng Zhou, Weimin Liu
Summary: The effect of amphiphobic surfaces on the rheological behavior and boundary slip of shear thickening fluids (STFs) was investigated through experiments and simulations. The results revealed significant influences on viscosity, shear thickening, and drag reduction, with a linear relationship between slip length and viscosity established.
TRIBOLOGY INTERNATIONAL
(2022)
Article
Physics, Fluids & Plasmas
Songsong Ji, Hongyuan Li, Zengzhi Du, Pengyu Lv, Huiling Duan
Summary: In this study, a theoretical framework is established to solve the interfacial coupled flow problem on a microstructured surface with slip boundary. By finding integral relation between the slip velocity and the slip velocity gradient, we solve the slip problem under the low-Reynolds-number limit. It is found that a small viscosity ratio, large fluid interfacial fraction, or large depth-to-width ratio of a groove can result in a large vorticity flux in the groove, leading to a large slip length. Therefore, we propose a method to enhance the slippage by introducing a jet flow in the grooves, which is verified by our theory. This study provides a new method for theoretically solving the coupled flow problem and can be extended to cases of high-speed flow.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Mechanics
Haichang Yang, Binglin Zeng, Xuehua Zhang, Yaowen Xing, Xiahui Gui, Yijun Cao
Summary: Enhancing boundary slip using interfacial nanobubbles (INBs) has been extensively studied in nanofluidic transport. This study investigates the influence of INBs on boundary conditions for both smooth and rough substrates using molecular dynamics simulations. The results show that INBs increase the slip length on a smooth substrate, with a linear increase observed with increasing surface coverage. On a rough substrate, the protrusion angle, quantity, and fluidity of INBs play a crucial role in determining the slip length. In addition, the fluidity of gas molecules inside the INBs dominates the enhancement of slip length.
Article
Engineering, Mechanical
Xinwei Wang, Yufei Wang, Haiping Tian, Nan Jiang
Summary: The study demonstrates that the anisotropy superhydrophobic surface has a significant impact on the turbulent boundary layer, resulting in well-fitted wall friction velocity, drag reduction rate, slip velocity, among other effects. Large-scale structures in motion on the superhydrophobic surface show upright wave packet structures and changes in convection velocity, structure morphology, and shear layer distortion.
ACTA MECHANICA SINICA
(2021)
Article
Engineering, Mechanical
Dayong Li, Yutong Ji, Ziqun Zhang, Yong Li
Summary: A comprehensive investigation on the distribution and morphology of interfacial gas bubbles and their effects on the boundary slip of fluid flow was conducted using finite element simulation. The results showed that the dispersion, protrusion angle, coverage area, size, height, and quantity of the interfacial gas bubbles play crucial roles in determining the slip length.
TRIBOLOGY INTERNATIONAL
(2023)
Review
Chemistry, Physical
Ivan U. Vakarelski, Fan Yang, Sigurdur T. Thoroddsen
Summary: The outcome of bubble collision is determined by hydrodynamic interaction forces, influenced by the tangential mobility of gas-liquid interfaces. Bubbles with mobile surfaces coalesce easier due to lower hydrodynamic resistance, resulting in stronger rebound from a mobile liquid interface with lower viscous dissipation.
CURRENT OPINION IN COLLOID & INTERFACE SCIENCE
(2022)
Article
Energy & Fuels
Yuan Si Tian, Zi Qiang Yang, Sigurbur T. Thoroddsen, Ehab Elsaadawy
Summary: The separation of water droplets from water-in-crude-oil emulsions is crucial in the petroleum industry. A new experimental method involving optical-access flow, Near-Infrared laser illumination, and high-speed video imaging can help select the optimal demulsifier concentration by quantifying coalescence probability.
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
(2022)
Article
Chemistry, Multidisciplinary
Ivan U. Vakarelski, Kenneth R. Langley, Fan Yang, Sigurdur T. Thoroddsen
Summary: This study examines the accuracy of numerical simulations in predicting the dynamics of thin liquid film drainage during the collision of bubbles or droplets. Experimental investigations of millimetric bubbles colliding with a flat glass interface in pure water were compared with numerical simulations using the open source Gerris flow solver. The simulation results showed excellent agreement with experimental observations in terms of the bounce trajectory and thin liquid film profile. The study highlights the potential of numerical simulations in resolving the complex processes of high velocity bubble and droplet collisions.
Article
Chemistry, Multidisciplinary
Adair Gallo, Nayara H. Musskopf, Xinlei Liu, Ziqiang Yang, Jeferson Petry, Peng Zhang, Sigurdur Thoroddsen, Hong Im, Himanshu Mishra
Summary: Recent research on the formation of hydrogen peroxide (H2O2) in water microdroplets has attracted significant attention. The presence of ozone (O-3) in the air has been found to have the most significant impact on H2O2 formation in these water microdroplets. Increased gas-liquid surface area facilitates the conversion of O-3 into H2O2.
Article
Engineering, Chemical
Yuan Si Tian, Er Qiang Li, Ehab Elsaadawy, Jia Ming Zhang, Ivan U. Vakarelski, Sigurdur T. Thoroddsen
Summary: In this study, microfluidic techniques were used to investigate the coalescence dynamics of water-in-oil emulsions in a simple shear flow. Experimental results showed a strong correlation between the coalescence time and the droplet approach velocity, effective diameter, offset, and continuous-phase viscosity. A scaling law for the dimensionless time needed for coalescence was also revealed.
CHEMICAL ENGINEERING SCIENCE
(2022)
Article
Chemistry, Physical
Ivan U. Vakarelski, Farrukh Kamoliddinov, Sigurdur T. Thoroddsen
Summary: This study investigates the interaction between millimeter-sized bubbles and the seawater-air interface in seawater samples collected from the Red Sea coastal area. It demonstrates that high concentrations of electrolytes and organics in seawater do not affect the mobility of the bubble interfaces during free-rise and bouncing.
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
(2022)
Article
Mechanics
Yuan Si Tian, Zi Qiang Yang, Sigurdur T. Thoroddsen
Summary: Fast microjets can be produced when drop-impact craters rebound or when a bubble bursts, and they play a crucial role in climate and olfactory senses as a source of aerosols. The most unique and fastest jets are generated when a small dimple forms at the crater bottom and rebounds without pinching off a small bubble. High-resolution numerical simulations reveal a new focusing mechanism that explains the extreme sensitivity to initial conditions observed in experiments of this phenomenon.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Materials Science, Multidisciplinary
Esraa Fakeih, Andres A. Aguirre-Pablo, Sigurdur T. Thoroddsen, Khaled N. Salama
Summary: This study investigates the design and fabrication of porous microneedles (MNs) and finds that injection through porous MNs results in a broader diffusion spread compared to hollow MNs. Three different designs of porous MNs with a constant pore size and controlled pore locations are fabricated using two-photon polymerization (2PP), and factors such as diffusion spread, mixing capabilities, and mechanical resilience are examined. The results show that porous MNs can cover 16 times the injection area of hollow MNs and demonstrate good mixing capabilities and mechanical strength.
ADVANCED ENGINEERING MATERIALS
(2023)
Article
Mechanics
Farrukh Kamoliddinov, Ivan U. Vakarelski, Sigurdur T. Thoroddsen, Tadd T. Truscott
Summary: In this experimental study, we investigated the hydrodynamics of a buoyant sphere accelerated along an air-water interface. The sphere displayed different behaviors depending on its speed, from floating on the surface to oscillating underwater and generating air cavities. These underwater air cavities were attached to the sphere surface near the laminar flow separation point. By changing the pulling angle and counterweight-induced velocity, we explored the effects on the hydrodynamics. Additionally, we analyzed the complex fluid-solid interactions and the influence of the air cavity on drag and lift coefficients and overall sphere hydrodynamics, particularly above the critical Froude number of 1.2.
Review
Chemistry, Multidisciplinary
Andris Sutka, Linards Lapcinskis, Delong He, Hyunseung Kim, Joseph D. Berry, Jinbo Bai, Maris Knite, Amanda V. Ellis, Chang Kyu Jeong, Peter C. Sherrell
Summary: This review summarizes the structure-property-performance relationship of polymer insulators in triboelectric nanogenerators and focuses on tools to enhance charge generation by altering the mechanical, thermal, chemical, and topographical properties of polymers. The use of additives to manipulate the polymer surface structure is also discussed. The link between these properties and the charging mechanism is explored, and pathways to engineer triboelectric charging are highlighted.
ADVANCED MATERIALS INTERFACES
(2023)
Article
Chemistry, Physical
Zi Qiang Yang, Peng Zhang, Meng Shi, Ali Al Julaih, Himanshu Mishra, Enzo Di Fabrizio, Sigurdur T. Thoroddsen
Summary: Polymer filaments have important applications in biology, tissue engineering, and molecular machines. Researchers have developed a simple method to deposit stretched polymer fibers between micro-pillars, allowing for characterization of filament-forming configurations and their properties.
Article
Physics, Fluids & Plasmas
Ahmed Al Brahim, Sigurdur T. Thoroddsen
Summary: This study focuses on the dynamical rearrangement of a multilayer fluid in a Hele-Shaw cell, and observes various dynamics of stirring and breakthrough. The study reveals that air can break through a high viscosity layer and erupt as a hemisphere into a lower-viscosity layer, accompanied by high-speed airflow. Using high-speed video, the details of the eruptions and the key roles of wetting, contact lines, and three-dimensionality are characterized. Additionally, the study finds counterflows in the center-of-mass trajectories and the interchangeability of top and bottom layers through intermediate layers.