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An accurate estimation of three-dimensional (3D) temperature fields in channel flows is challenging but critical for many important applications such as heat exchangers, radiation energy collectors, and enhanced geothermal systems. In this paper, we demonstrate the possibility of inferring temperature fields from concentration fields for laminar convection flows in a 3D channel using a machine learning (ML) approach. The study involves generation of data using 3D numerical simulations, application of deep learning methodology using conditional generative adversarial networks (cGANs), and analysis of how dataset selection affects model performance. The model is also tested for applicability in different convection scenarios. Results show that cGANs can successfully infer temperature fields from concentration fields, and the reconstruction accuracy is sensitive to the training dataset selected. In this study, we demonstrate how ML can be used to overcome the limitations of traditional heat and mass analogy functions widely used in heat transfer research. [ABSTRACT FROM AUTHOR]

Summary: In order to make networks more adaptable and flexible, software‐defined networking (SDN) is an architecture that abstracts the many, easily distinct layers of a network. By enabling businesses and service providers to react swiftly to shifting business requirements, SDN aims to improve network control. SDN has become an important framework for Internet of Things (IoT) and 5G. Despite recent research endeavors focused on pinpointing constraints within SDN design components, various security attacks persist, including man‐in‐the‐middle attacks, host hijacking, ARP poisoning, and saturation attacks. Overcoming these limitations poses a challenge, necessitating robust security techniques to detect and counteract such attacks in SDN environments. This study is dedicated to developing a method for detecting and mitigating control plane attacks within Software Defined Network Environments utilizing Deep Learning Algorithms. The study presents a deep‐learning‐based approach to identifying malicious hosts within SDN networks, thus thwarting unauthorized access to the controller. Experimental results demonstrate the effectiveness of the proposed model in host classification, exhibiting high accuracy and performance compared to alternative approaches. [ABSTRACT FROM AUTHOR]

In the process of natural gas hydrate exploitation, the secondary hydrate formation may occur in both the reservoir and the completion layer. The secondary hydrate formed during the exploitation process and the sand particles falling from the reservoir will block the flow channel and reduce the gas production. In this paper, the permeability change of sand filling layer under the influence of sand and hydrate blockage is studied from a three-dimensional perspective, and the permeability change characteristics of sand mixing and secondary hydrate formation in filling layer caused by pore space blockage are summarized. A three-dimensional model for predicting the permeability of gravel layer is developed. In previous studies, the mathematical model parameters derived from the empirical formula are always not unique, which will cause inaccurate permeability prediction results. In this study, the simulated annealing algorithm is used to optimize the parameters such as boundary conditions and cooling tables. The undetermined parameters in the existing mathematical prediction model of gravel layer permeability are optimized into a determined maximum value to solve the optimization problem of the undetermined parameters of the permeability model. The algorithm in this paper takes the actual value of gravel layer permeability with different sand content and hydrate concentration in the experiment as the standard, and takes the mean square error of the predicted value and the experimental value of the prediction model as the objective function. The simulated annealing algorithm is used to estimate and optimize the undetermined parameters of the model. The algorithm results show that the mean square error between the predicted value and the experimental value is minimized with n = 22.7 and τ = 1.014(n and τ are the parameters to be optimized in the permeability model of this paper). The fitting degree between the optimized permeability prediction model and the experimental value is higher than that before optimization, which verifies the correctness and rationality of the algorithm in this paper. • Simulated annealing algorithm is used to optimize the permeability model. • The simulated annealing algorithm is optimized to have faster solution speed. • The NMSE error calculation method is used to make the predicted permeability model better fit the actual value. • The optimized model is combined with the capacity model. [ABSTRACT FROM AUTHOR]

The objective of the study is to use a 3D Acoustic Doppler Velocimeter (ADV) to gauge the typical flow and turbulence characteristics within a non-uniform open channel. The findings of experimental examinations of the subcritical flow along the channel are presented in this work. The behavior of sand grains in turbulent open channel flow across porous and rough bed surfaces was examined in laboratory research, and the results were obtained. The properties of turbulent flow, i.e., turbulence intensity, turbulent kinetic energy, and Reynolds shear stresses, are determined from ADV data. The continuity equation and the Reynolds equation of open-channel flow have been used to build theoretical formulations for the velocity distribution and Reynolds stress distribution in the vertical direction. Measured profiles of vertical velocity and Reynolds stress are compared to the derived expressions. The impact of the size of particles on the distribution of mean flow characteristics is discussed. This work provides a novel origin for the profile and analyzes the behavior of the vertical velocity distribution in the region where fully formed turbulence is dominating in open channels using the Navier–Stokes equations. In comparison to other sand roughness, Chopan sand bed (with greater density) exhibits the strongest turbulence intensities in both vertical and streamwise direction just next to the bed when away from the channel boundary. In contrast to flow across a rough surface, the variance ranges between 150 and 250% concerning the channel bed's roughness type, impacting the velocity triple products that signifies transfer of turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

In this work, a steady-state, three-dimensional and non-isothermal numerical model for a proton exchange membrane electrolysis cell (PEMEC) is established. Based on this model, the distribution of catalyst loading is specifically designed according to the flow characteristics of both parallel and serpentine channels. In general, the catalyst loading is progressively reduced from inlet to outlet along the flow direction to match the local water content, leading to an innovative segmented catalyst layer which has not been studied yet for PEMEC applications. The electrochemical behavior of different segmentation schemes is investigated by comparing their polarization curves normalized by either electrode area or catalyst loading, while other physical fields such as velocity, pressure, water mole fraction and temperature distributions are also characterized. The numerical results reveal that a reasonable distribution of catalyst can reduce its amount of usage while still maintaining most of the PEMEC performance. In other words, the cost performance is significantly improved. This is mainly attributed to the full use of uneven water distribution in the flow channel, which improves the catalyst utilization efficiency significantly. This strategy is proved to be effective for both serpentine and parallel channels, ensuring a broad application prospect. • A novel catalyst layer segmentation strategy is proposed for PEM electrolyzer. • The catalyst loading is distributed according to the local water content. • Specific current normalized by catalyst weight is improved due to loading reduction. • Physical field distribution inside the PEM electrolyzer is not changed too much. • Cost performance of the PEM electrolyzer is improved significantly. [ABSTRACT FROM AUTHOR]

Liquid hydrogen plays a critical role in large-scale hydrogen storage and long-distance transport. The primary cost associated with liquid hydrogen supply is attributed to the liquefaction consumption. The hydrogen turbo-expander, a pivotal component in industrial hydrogen liquefaction plants, is instrumental in determining liquefaction costs. Improving the efficiency of the expander offers a significant opportunity for cost reduction. This paper commences by validating the loss model employed to assess the hydrogen turbo-expander using numerical simulation results. Subsequently, a regional division model is introduced for the expander impeller passage to identify the locations of various losses. Under diverse operational conditions, the boundaries of regions are determined through a comparison between the loss model and numerical simulation. Finally, an examination of losses in the hydrogen turbo-expander is conducted using Computational Fluid Dynamics (CFD) results under varying operating conditions, yielding the following insights. With an increase in the expansion ratio of the hydrogen turbo-expander, the isentropic efficiency initially rises and then declines. Among the various losses observed under variable working conditions, incidence loss emerges as the most critical factor. When the expansion ratio is small, a negative attack angle forms at the impeller inlet, causing chaotic flow within the channel and an increase in passage loss. • Correlations in loss model are validated for hydrogen turbo-expanders. • The proposed regional division model enables a quantitative loss analysis. • Efficiency decays more severely with the expansion ratio lower than design value. • Incidence loss is the primary driver for efficiency decline far from design condition. [ABSTRACT FROM AUTHOR]

Bipolar plates are one of the most important components of proton exchange membrane fuel cells. With the miniaturization of bipolar plate flow channel sizes and the increasing demand for precision, springback has become a key focus of research in the bipolar plate forming process. In this paper, the hydroforming process for 316L stainless steel bipolar plates was studied, and an FEM model was built to examine the stress and strain at various locations on the longitudinal section of the plate. Modeling accuracy was validated by the comparison of experimental profile and thickness distribution. The effects of forming pressure and grain size on springback behavior are discussed. The results show that with increasing forming pressure, the springback value decreases initially, followed by an increase, but then again decreases. When the forming pressure is 80 MPa–100 MPa, the deformation of the lower element of the upper rounded corner is not uniform with more elastic regions, and the springback is positively correlated with forming pressure. The springback distribution pattern on the cross-section of the bipolar plate changes from a normal distribution to a distribution of "M" shape with increased pressure. The larger the grain size, the lower the yield strength elastic proportion, resulting in a decrease in springback of the sheet. The maximum amount of springback of the bipolar plate is 3.1 μm when the grain size is 60.7 μm. The research results provide a reference for improving the forming quality of metal bipolar plates with different flow channel shapes. [ABSTRACT FROM AUTHOR]

This article presents the first use of shape forming elements (SFEs) to produce architected composites from multiple materials in an extrusion process. Each SFE contains a matrix of flow channels connecting input and output ports, where materials are routed between corresponding ports. The mathematical operations of rotation and shifting are described, and design automation is explored using Bayesian optimization and genetic algorithms to select fifty or more parameters for minimizing two objective functions. The first objective aims to match a target cross-section by minimizing the pixel-by-pixel error, which is weighted with the structural similarity index (SSIM). The second objective seeks to maximize information content by minimizing the SSIM relative to a white image. Satisfactory designs are achieved with better objective function values observed in rectangular rather than square flow channels. Validation extrusion of modeling clay demonstrates that while SFEs impose complex material transformations, they do not achieve the material distributions predicted by the digital model. Using the SSIM for results comparison, initial stages yielded SSIM values near 0.8 between design and simulation, indicating a good initial match. However, the control of material processing tended to decline with successive SFE processing with the SSIM of the extruded output dropping to 0.023 relative to the design intent. Flow simulations more closely replicated the observed structures with SSIM values around 0.4 but also failed to predict the intended cross-sections. The evaluation highlights the need for advanced modeling techniques to enhance the predictive accuracy and functionality of SFEs for biomedical, energy storage, and structural applications. [ABSTRACT FROM AUTHOR]

Flooding results in short and long-term modifications of aquatic ecosystem structure and biodiversity. Cyclone Idai, which ravaged through Zimbabwe in 2019, had devastating consequences on aquatic ecosystems. However, the extent of habitat modification and consequent biodiversity shifts are unknown. This study focuses on the comparative analysis of (i) habitat structure and (ii) macroinvertebrate assemblages in headwater streams of the Odzi sub-catchment, Chimanimani District, Zimbabwe, specifically examining the conditions post-Cyclone Idai-induced flooding. Field sampling was conducted in the dry season (September−November) 2019 and wet season (January−March) 2020. Headwater streams of the Murare (first order), Umvumvumvu (first and second order) and Nyanyadzi (first and second order) rivers were sampled. Habitat assessment was done following the Benthic Macroinvertebrate Monitoring Protocol Implementation Plan. Selected water variables were measured using appropriate probes. Macroinvertebrate assemblage data were collected using the South African Scoring System (SASS 5) protocol. Spatiotemporal variations in water quality, habitat structure and macroinvertebrate metrics were assessed using two-way ANOVA, ANOSIM and SIMPER. Significant spatiotemporal heterogeneity (p < 0.05) was detected in temperature, turbidity, conductivity and total dissolved solids, velocity and depth regimes, channel flow status, sediment deposition, channel alteration and frequency of riffles for the three rivers. Habitat quality ascending hierarchical order was: Umvumvumvu > Murare > Nyanyadzi after Cyclone Idai induced flooding. The highest macroinvertebrate composition diversity was detected in Murare River, the least flood-affected stream. The largest dissimilarity (ANOSIM, 75.3%) was between the Umvumvumvu and Nyanyadzi rivers. Macroinvertebrate community structure differed significantly because of species uniqueness and heterogenous tolerance to changes in environmental conditions after flooding. Flooding intensity and duration induces dissimilar environmental tolerances and persistent macroinvertebrates communities in lotic systems across local catchment scales. Long-term assessment of water quality impairment, resilient functional feeder groups and rifflescale physical habitat structure are imperative for optimised micro-scale conservation of macroinvertebrates in headwater streams prone to flash flooding. [ABSTRACT FROM AUTHOR]

The inefficiency and poor performance of drainage system is increasing considerable among causes of urban floods. This study focuses on the influence of the aperture ratio on drainage capacity through the 170 local numerical models and 46 physical model tests. Four regions of water characteristic were obtained: Open Channel Flow Non-Overload (OC-NOL), Full Flow Overload (F-OL), Full Flow Overload Affected (F-OLe) and Full Flow Overflow (F-OF). The findings were applied in a practical case, which showed that: pipe diameter had an evident effect than manhole diameter. As the aperture ratio increased, the flood areas with low water depth grades evolved faster towards higher grades, while the drainage capacity decreased. Manhole overflow seriously increases the risk of flood when the pipe diameter was below 0.4 m or aperture ratio was above 2.00. This paper explains the water characteristic from the perspective of aperture ratio, which provides supplementary information for flood risk assessment. [ABSTRACT FROM AUTHOR]

The current article investigates the effects of nonlinear mixed convection flow in an upright channel with asymmetric or symmetric heating and cooling conditions, considering the influence of temperature-dependent thermal conductivity. The momentum equation is approximated using the nonlinear Boussinesq approximation in the buoyancy force term. Computational solutions for the dimensionless partial differential equations are obtained through the use of an unconditionally stable and convergent implicit finite difference technique. A regular perturbation series approach is employed to ascertain steady-state solutions, facilitating the assessment of the correctness of the numerical approach. During the numerical computing process, it is observed that the nonlinearity in density variation with temperature, along with the mixed convection parameter and the symmetric or asymmetric heating and cooling of the plates, significantly influences flow generation. It is also noted that in the scenario of asymmetric heating, fluid motion is stronger at the bottom plate, whereas in the case of symmetric heating/cooling settings, the highest velocity is observed in the center of the channel. [ABSTRACT FROM AUTHOR]

An air-entraining vortex begins to form when the submergence of an intake is not adequate and less than the critical value known as critical submergence. In the present study, critical submergence for a laterally placed single rectangular intake under a uniform approach flow in an open channel was investigated experimentally. Analysis of the data collected in the present study reveals that critical submergence is significantly influenced by intake size, intake aspect ratios, approach Froude number, intake Froude number, intake Reynolds number, and Weber number. However, intake Froude number and intake aspect ratio were found to be the most sensitive parameters that affect critical submergence. An empirical relationship for critical submergence has been developed using collected data used to compute the critical submergence within an error of ±20%. The findings of this investigation is advantageous for hydraulic engineers when designing lateral rectangular intakes to prevent the formation of an air-entraining vortex. Practical Applications: Insufficient water cover over the hydraulic intakes causes an air-entraining vortex formation in the vicinity of the intake. The formation of such an air-entraining vortex results in significant hydraulic issues, structural damages, etc. Ensuring enough submergence for the intake during its operational period is necessary to evade such problems. The submergence at which the air-core tail of the surface vortex reaches the intake initiating air-entrainment is called critical submergence. Critical submergence is an important parameter for the design of intakes and is widely used as a parameter to determine an incipient state for which no air is entrained by intake vortices. This paper discusses the experimental investigation of critical submergence for single lateral rectangular intakes concerning significant geometrical parameters, such as intake aspect ratio, approach Froude number, intake Froude number, etc. The proposed empirical equations in this study are helpful to hydraulic engineers when computing critical submergence to fix the invert level of a lateral rectangular intake. [ABSTRACT FROM AUTHOR]

Flow boiling heat transfer is a promising technology for thermal management. In this paper, flow boiling heat transfer characteristics in a rectangular vertical flow channel are experimentally and numerically investigated at low flow rate. Visualization results provide guidance for the prediction of flow patterns. The flow boiling correlation at low flow rates is improved with an error of less than 30%. Numerical results reveal vortices enhanced local heat transfer. Absolute vorticity is introduced to quantify the secondary flow. The results indicate that the secondary flow intensity increases with heat flux, verifying that boiling flow produces the local convection enhancement. [ABSTRACT FROM AUTHOR]

Reservoir heterogeneity, water-oil mobility ratio, cementation degree, and strong injection and production significantly influence long-term waterflooding and polymer flooding processes in oil reservoir development, leading to the formation of low-resistance dominant seepage channels in the lower part of thick oil layers without internal laminations. Understanding the spatial distribution and evolution of dominant seepage channels in oil reservoirs during waterflooding and polymer flooding is crucial for improving reservoir development and recovery rates. It uses a streamlined numerical simulation method to quantitatively show the spatial and temporal distribution of dominant seepage channels in the oil reservoir. A model and chart were created to demonstrate the relationship between permeability and throat radius, capturing changes in reservoir permeabilities over time. The study developed a comprehensive mathematical model to identify dominant seepage channels, considering parameters such as inter-well flow ratio, injection efficiency, permeability change value, and water saturation. Research findings indicate a 14.8 % increase in reservoir permeability after polymer flooding, with slight changes in porosity and a 20.3 % decrease in clay content. The established mathematical model and identification criteria were used to comprehensively quantitatively evaluate flow channels, describing the distribution characteristics and evolution process of dominant seepage channels in the experimental area over four periods: pre-polymer flooding, low water-saturation period during polymer flooding, post-polymer injection, and subsequent 10 years of water flooding. Both polymer flooding and subsequent water flooding have significantly altered the distribution pattern of predominant fluid pathways: 254 well layers now demonstrate robust predominant fluid pathways (19 %); another 272 well layers feature moderately predominant fluid pathways (22 %); while an additional 440 well layers display weaker predominant fluid pathways (approximately 35 %). There has been a noticeable increase in both weak and moderate predominant fluid pathways, which are now more widespread in the area. However, localized occurrences of strong predominant fluid pathways persist with no significant change in their distribution characteristics. Analysis at four different time points shows a clear trend of increasing intensity as we move from polymer to subsequent water flooding in this decade. Additionally, examination along an axis from upper left to lower right reveals a linear progression that indicates clear connections among different categories of dominant seepage channel. The verification results show a strong correlation between the calculated dominant seepage channel distribution and actual water-injection profile test results, indicating that the method effectively identifies dominant seepage channels in oil reservoirs after polymer flooding and has the potential to enhance oil recovery further. [ABSTRACT FROM AUTHOR]

Surfactants are commonly employed in sand‐based turfgrass systems to address soil water repellency, which often results in the formation of preferential flow channels leading to non‐uniform wetting patterns. While the influence of soil moisture on nutrient dynamics is well documented, the potential of surfactants to improve N uptake remains poorly understood. A 2‐year study was conducted on 'Celebration' bermudagrass [Cynodon dactylon (L.)] fairway to better understand the interaction between fertility programs (296 or 586 kg N ha−1 year−1 from ammonium sulfate and 564 kg N ha−1 year−1 primarily from a controlled‐release N fertilizer) and surfactant rate and frequency (3.2 L ha−1 every 14 or 28 days, or at 6.4 L ha−1 every 28 days) on turfgrass performance, leaf N content, and soil moisture. Overall, no significant interaction was observed between surfactant treatment and fertility program. During the dry season (November to May), fertility programs influenced turfgrass performance parameters with higher N rates consistently leading to improvements in visual quality, normalized difference vegetation index, percent green cover, and dark green color index; however, no differences were observed during the rainy season (June to October). Surfactants showed no effect on turfgrass performance but led to minimal increase in leaf N content from 3.72% to 3.85%. All surfactant treatments reduced water drop penetration time at 0 cm. Moreover, surfactant treatments applied every 28 days regardless of the rate exhibited a higher volumetric water content compared to those applied every 14 days. Surfactant applications might not be an economically feasible strategy to improve leaf N content in South Florida well‐watered bermudagrass fairways. Core Ideas: Surfactant applied at half rate had the same effect as full rate on soil moisture and water penetration.Surfactant applications might not be necessary to improve leaf N content in South Florida fairways.Higher N rates sustained bermudagrass quality over winter.Leaf N content within optimal ranges did not always translate to sufficient optimal turfgrass quality. [ABSTRACT FROM AUTHOR]

Although flow mixing and cooling can be greatly enhanced when considering the use of fluidic oscillators (FOs), they are more commonly employed in active flow control (AFC) applications where the injected pulsating flow interacts with the boundary layer, usually in order to delay its separation. In fact, prior to any FO implementation in a given application, it is essential to study the range of frequencies and amplitudes it can generate as a function of the incoming mass flow and its dimensions. This is what is being performed in the present manuscript for a rather novel FO configuration. A numerical study of a standard three-dimensional (3D) FO configuration, and also using a two-dimensional (2D) approach, is initially presented. After comparing the 3D and the 2D results and analyzing the main differences, we modified some of the internal dimensions of the FO in order to evaluate the variation in its dynamic performance. The present results clarify which internal dimensional modifications are more effective in generating larger output frequencies and velocity field variations. Care is taken to analyze the origin of self-sustained oscillations. This paper links, for the first time, the origin of the pressure force oscillations at the feedback channel's outlet, with the interaction of the mixing chamber central jet and the reverse feedback channel flow at the mixing chamber's converging walls. A novel equation relating the FO outlet mass flow frequency with the time-averaged FC reverse flow is presented and discussed. In fact, the present study needs to be seen as the continuation of a former one, recently published by authors, where the effects of several Reynolds numbers as well as some different internal dimensions were considered. [ABSTRACT FROM AUTHOR]

This experimental study considers the exchange flow of two miscible fluids in a rectangular channel. The main purpose is to understand the mixing dynamics and explore how mixing and different channel inclinations can affect variations in front velocity. In contrast to previous studies, no steady state is assumed. The larger channel cross-section used in the current study provides an opportunity to visualize and analyze the inertia dominated regime in finer details. For horizontal channels, after opening the gate valve and allowing the transient phase to pass, it is observed that the front velocity remains almost constant for a period before gradually decreasing. In inclined flows, the mixing and transition to inertia dominated flow begin when the viscous flow rate of the main flow increases. This flow rate may exceed the maximum flow rate that the front can tolerate according to the equations describing the momentum balance at the front. At sufficiently high density contrasts or large inclinations, the front velocity may continue to decrease as the flow progresses due to interfacial instabilities and mixing. Under such conditions, the results may also cast doubt on the presence of a true steady state front velocity in miscible exchange flow. [ABSTRACT FROM AUTHOR]

To study the water management of natural rivers, two-dimensional (2D) hydrodynamic models have become essential tools. The performance of five different hydrodynamic modelling packages, SRH 2D (developed by U.S. Bureau of Reclamation), Delft 3D (developed by Deltares), FESWMS (developed by Federal Highway Administration), MIKE 21 FM (developed by DHI), and Hec Ras 2D (developed by US Army Corps of Engineers) was evaluated in this study. Numerical solutions to shallow water equations were obtained using finite elements, finite differences, and finite volumes. This work aims to provide the most accurate and objective information that can help select two-dimensional models for different annual scenarios. This study focused on comparing annual flow cases in-channel rather than flood flow. A study area on the Nile River was selected for this study. A performance assessment has been conducted based on the calibration of the model, the representation of the channel flow, and the computing efficiency of the model. The results show that Delft 3D and SRH 2D models were the most compatible with the measured data. Delft 3D model outperforms SRH 2D in computational efficiency up to 66% times faster. [ABSTRACT FROM AUTHOR]

In this study, the effect of baffle configuration on the water disinfection efficiency of a planar photoreactor equipped with ultraviolet C light-emitting diodes (UV-C LEDs) was investigated. The results indicated that the configuration of the baffles influenced the hydrodynamics inside the flow channel and thus affected the microbial trajectory, and exposure time. Accordingly, a modified serpentine configuration was developed to enhance the UV light exposure of microbes in water and improve the reactor performance for microbial inactivation. According to the simulation results, the quarter-circle baffles used in the modified serpentine configuration increased the microbial path length along the flow channel. However, because the cross-sectional area of the flow channel decreased, this configuration increased the water velocity. A modified serpentine configuration with a baffle radius of 5 mm achieved the longest microbial exposure time and highest inactivation value for Escherichia coli. At a water flow rate of 160 mL/min, this configuration achieved a UV fluence of 15.2 mJ/cm2 and an inactivation value of 3.8 log, which were approximately 22% and 0.4 log higher than those obtained with the traditional serpentine configuration, respectively. In addition, the maximum water flow rate at which the UV reactor achieved an inactivation value of 4.0 log was 154 mL/min at a baffle radius of 5 mm. This flow rate was 11.5% higher than that obtained with the traditional serpentine configuration. These close agreements between the experimental and simulation results confirmed the strong capability of the proposed modified serpentine configuration to improve reactor performance. [ABSTRACT FROM AUTHOR]

In a fuel cell, flow channels are crucial components responsible for various essential functions that enable the system to operate effectively. The design of a directly coupled flow channel in a Proton Exchange Membrane Fuel Cell (PEMFC) system, assuming deterministic parameters, has been extensively studied. However, this deterministic approach neglects the inherent uncertainties in system performance during real-life operation, resulting in potentially unreliable and suboptimal performance. To address this issue, we propose a reliability-based design optimization (RBDO) of the PEMFC's channel structure, considering uncertainties in operating parameters. This paper presents a numerical model of the PEMFC in COMSOL, deterministic designs, reliability-based designs and a global sensitivity analysis on the PEMFC cell's potential output and average water activity on the membrane. Although the RBDO approach shows a reduction in cell efficiency compared to the deterministic design, it significantly improves reliability, with increases from 60.92% to 95.10% for cell potential and from 79.31% to 96.85% for water activity. [ABSTRACT FROM AUTHOR]

Interactions between carbon nanotubes (CNTs) and fluid flows are central to the operation of several emerging nanotechnologies. In this paper, we explore the fluid-structure interaction of CNT micropillars in wall-bounded shear flows, relevant to recently developed microscale wall shear stress sensors. We monitor the deformation of CNT micropillars in channel flow as the flow rate and wall shear stress are gradually varied. We quantify how the micropillars bend at low wall shear stress, and then will commonly tilt abruptly from their base above a threshold wall shear stress, which is attributed to the lower density of the micropillars in this region. Some micropillars are observed to flutter rapidly between a vertical and horizontal position around this threshold wall shear stress, before settling to a tilted position as wall shear stress increases further. Tilted micropillars are found to kink sharply near their base, similar to the observed buckling near the base of CNT micropillars in compression. Upon reducing the flow rate, micropillars are found to fully recover from a near horizontal position to a near vertical position, even with repeated on–off cycling. At sufficiently high wall shear stress, the micropillars were found to detach at the catalyst particle-substrate interface. The mechanical response of CNT micropillars in airflow revealed by this study provides a basis for future development efforts and the accurate simulation of CNT micropillar wall shear stress sensors. [ABSTRACT FROM AUTHOR]

Graphene field‐effect transistors (GFETs) are widely used in biosensing due to their excellent properties in biomolecular signal amplification, exhibiting great potential for high‐sensitivity and point‐of‐care testing in clinical diagnosis. However, difficulties in complicated fabrication steps are the main limitations for the further studies and applications of GFETs. In this study, a modular fabrication technique is introduced to construct microfluidic GFET biosensors within 3 independent steps. The low‐melting metal electrodes and intricate flow channels are incorporated to maintain the structural integrity of graphene and facilitate subsequent sensing operations. The as‐fabricated GFET biosensor demonstrates excellent long‐term stability, and performs effectively in various ion environments. It also exhibits high sensitivity and selectivity for detecting single‐stranded nucleic acids at a 10 fm concentration. Furthermore, when combined with the CRISPR/Cas12a system, it facilitates amplification‐free and rapid detection of nucleic acids at a concentration of 1 fm. Thus, it is believed that this modular‐fabricated microfluidic GFET may shed light on further development of FET‐based biosensors in various applications. [ABSTRACT FROM AUTHOR]

Plasmons in two-dimensional electron channels have potential applications in the terahertz frequency range. Equivalent circuit models provide a convenient framework for analysing the plasmons. This article introduces a circuit model for plasmons in the presence of a dc current that flows in a gated channel. It is shown that drifting plasmons can be described by an LC-transmission line with distributed dependent sources. A circuit analogue of the Dyakonov–Shur instability is demonstrated. Then, a lumped-element transmission line with dependent sources is analysed, and non-reciprocity is demonstrated for examples of a right- and a left-handed transmission line. Effects of ohmic loss are discussed. The results could be used for the design of non-reciprocal transmission line devices. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'. [ABSTRACT FROM AUTHOR]

Where precision is paramount in managing temperature and fluid dynamics, micro heat exchangers (MHXs) emerge as indispensable tools. This review investigates the significance of MHX technology, offering readers a comprehensive roapmap from conceptualization to market application. We dissect the nuances of material selection, shedding light on cutting‐edge advancements poised to revolutionize MHX efficiency. Furthermore, we explore how the geometry of MHX influences heat transfer dynamics and pressure drop, providing insights into enhancing the overall effectiveness. We delve into the various types of control instrumentation, offering a detailed analysis of their applicability. Beyond the technical prowess, the economic landscape plays a pivotal role in the adoption of MHX technology. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) has attracted wide attention because its efficiency is not limited by the efficiency of Carnot cycle. The structure of flow channel in SOFC has great effects on the internal mass distribution, which influences current density. In this paper, the height of flow channel and the position, arrangement, number and height of the fin which is placed in channel, are changed to get different structures of bi-layer interconnector, and they are applied to three layers SOFC stack. The effects of each structural parameter on the current density are studied by numerical simulation. The results show that, increasing the number of fins and bi-layer interconnector height can make more reactant gas enters the electrode. In addition, compared with the conventional structure, the current density can be increased by the bi-layer interconnector up to 31.256%, and the bi-layer interconnector structure could save n-1 layers of interconnector, which reduces the volume of SOFC stack. Among the five structural parameters, the position of fins has the least influence on temperature distribution and current density, while the arrangement of fins has the highest influence on volume current density, reaching 30%. Using a staggered arrangement and higher bi-layer interconnector can also improve the temperature distribution. • A three-dimensional SOFC stack with bi-layer interconnector was established. • Changing geometry of fins and channel height to get different structures. • Increasing number of fins and channel height improve concentration distribution. • The arrangement of fins has the greatest impact on current density. • Staggered fins and higher bi-layer interconnector reduce the highest temperature. [ABSTRACT FROM AUTHOR]

Given the distinct water management requirements in anion-exchange membrane fuel cells (AEMFCs) and proton-exchange membrane fuel cells (PEMFCs), the necessity for tailored flow field redesign and analysis in AEMFCs becomes paramount. In this study, a three-dimensional, two-phase, non-isothermal AEMFC model is constructed to explore the impact of the channel shape of a parallel flow field on the cell performance. The results demonstrate that the channel shape notably influences cell performance at low voltages, and the cell performance follows: inverted trapezoidal > square > triangular > rectangular > trapezoidal > semicircular. A cell with inverted trapezoidal channels achieves a 12.9% increase in peak power density and an 83.4% reduction in current density non-uniformity compared to that with semicircular channels. Analysis of the evaluation criteria indicates that excellent heat transfer performance, superior mass transfer performance, and sufficient water content in the membrane are critical for improving AEMFC performance. • Effect of six channel geometries on the AEMFC performance is investigated. • EMTC, EEC, and inhomogeneity index are used to evaluate the whole performance. • Inverted trapezoidal channels yield the best overall performance. • Triangular channels result in the lowest EEC. [ABSTRACT FROM AUTHOR]

We introduce generative models for accelerating simulations of high-dimensional systems through learning and evolving their effective dynamics. In the proposed Generative Learning of Effective Dynamics (G-LED), instances of high dimensional data are down sampled to a lower dimensional manifold that is evolved through an auto-regressive attention mechanism. In turn, Bayesian diffusion models, that map this low-dimensional manifold onto its corresponding high-dimensional space, operate on batches of physics correlated, time sequences of data and capture the statistics of the system dynamics. We demonstrate the capabilities and drawbacks of G-LED in simulations of several benchmark systems, including the Kuramoto-Sivashinsky (KS) equation, two-dimensional high Reynolds number flow over a backward-facing step, and simulations of three-dimensional turbulent channel flow. The results demonstrate that generative learning offers new frontiers for the accurate forecasting of the statistical properties of high-dimensional systems at a reduced computational cost. The forecasting of critical phenomena in complex systems governed by partial differential equations remains challenging and computationally expensive. The authors propose a generative learning approach for the forecasting of the statistical properties of high-dimensional systems at a reduced computational cost. [ABSTRACT FROM AUTHOR]

AbstractIn all common heat transfer books, the Nusselt number (Nu) given for laminar fully developed incompressible flow in a plane channel with isothermal walls is Nu=7.54. This result is obtained through the neglect of viscous dissipation. However, we show that when the viscous dissipation is very small but not identically zero (which is a physical impossibility), the Nusselt number should be either Nu=35/2 for a liquid or Nu=0 for an ideal gas. Furthermore, the exact corresponding temperature distributions and mean temperatures for arbitrary viscous dissipation are given. [ABSTRACT FROM AUTHOR]

Given the low plugging success rate of existing plugging agents in oilfield applications, this study proposed a new selective plugging agent system (SA-1-S) with a high plugging efficiency, which dissolves in oil and releases oil flow channels under formation temperature conditions. Being insoluble in water and acid, it blocks water flow channels. In particular, at ambient temperature of 25 °C and reservoir temperature of 65 °C, the dissolution rate of SA-1-S particles in formation crude oil, kerosene, and diesel oil exceeded 96%, being suitable for formations at temperatures below 120 °C∼130 °C. The proposed agent's plugging rate exceeded 90% on cores and 80% under reverse kerosene action; this rate dropped under forward scouring by 2.01 ∼ 3.21%. The selective water plugging agent proposed in this paper has application prospects in improving the oil recovery in high water-bearing oil wells. [ABSTRACT FROM AUTHOR]

Fractures within granite may become channels for fluid flow and have a significant impact on the safety of waste storage. However, internal aperture variation under coupled conditions are usually difficult to grasp, and the inevitable differences between the measured data and the real fracture structure will lead to erroneous permeability predictions. In this study, two different CT (Computed Tomography) image processing methods are adopted to grasp internal fractures. Several CT images are extracted from different positions of a rock sample under different confining stresses. Two critical factors, i.e., aperture and the contact area ratio value within a single granite fracture sample, are investigated. Results show that aperture difference occurs under these two image processing methods. The contact area ratio value under two image processing methods has less than 1% difference without confining stress. However, there is larger than ten times difference when the confining stress increases to 3.0 MPa. Moreover, the edge detection method has the capability to obtain a relatively accurate internal fracture structure when confining pressure is applied to the rock sample. The analysis results provide a better approach to understanding practical rock fracture variations under various conditions. [ABSTRACT FROM AUTHOR]

Alkaline water electrolysis (AWE) holds considerable promise for large-scale hydrogen production. Decreasing energy input and improving efficiency are inevitable in its further commercial development. As one of the critical factors for reducing energy consumption, flow channel design on bipolar plates cannot be ignored. This study utilizes a three-dimensional model for alkaline electrolyzer that couples electrochemical reactions with mass and heat transfer to approximate the real physical process and achieve reliable convergence. Integrating diverse turbulence units tailored to different local flow demands, an advanced Partitioned Point Flow Channel (PPFC) structure is proposed aiming at optimizing electrolyte flow distribution. Results reveal that PPFC's unique combination of turbulence units promotes lateral flow and electrolyte mass transfer rate, increasing electrolyte flow uniformity and hydrogen removal efficiency by 17.5% and 24.4%, respectively. Further comparative analysis with traditional designs shows an average diaphragm temperature drop of 4 K and a current density increase of 10.7% at a cell voltage of 2 V. These results indicate that PPFC offers significant advantages in reducing energy loss in electrolyzer. • 3-D AWE model couples electrochemical reaction with mass and heat transfer is built. • Advanced PPFC integrates different turbulence units for diverse local flow demands. • PPFC improves flow uniformity by 17.5% and hydrogen removal efficiency by 24.4%. • PPFC reduces average temperature by 4 K and increases current density by 10.7%. [ABSTRACT FROM AUTHOR]

The article "Dynamics of turbulent energy and dissipation in channel flow" delves into the intricate relationship between turbulent kinetic energy (TKE), turbulence dissipation rate (TDR), and turbulence production rate (TPR) in fully developed turbulent channel flow. The research uncovers time lags between these variables, with correlations that vary based on Reynolds number. The findings emphasize the complex nature of energy transfer and dissipation within different regions of the channel, showcasing correlations that involve both time and wall-distance lags. This study offers valuable insights into the self-sustaining process of turbulent flows, with implications for understanding turbulence dynamics across various contexts. [Extracted from the article]

The document is a contents list for the journal "Lab on a Chip," which focuses on devices and applications at the micro- and nanoscale. It includes various articles and papers on topics such as microfluidics, robotics, bioprinting, and drug release. The journal aims to connect the world with the chemical sciences and is published by The Royal Society of Chemistry. [Extracted from the article]

This review summarizes programmable microfluidics, an advanced method for precise fluid control in microfluidic technology through microchannel design or liquid properties, referring to microvalves, micropumps, digital microfluidics, multiplexers, micromixers, slip-, and block-based configurations. Different microvalve types, including electrokinetic, hydraulic/pneumatic, pinch, phase-change and check valves, cater to diverse experimental needs. Programmable micropumps, such as passive and active micropumps, play a crucial role in achieving precise fluid control and automation. Due to their small size and high integration, microvalves and micropumps are widely used in medical devices and biological analysis. In addition, this review provides an in-depth exploration of the applications of digital microfluidics, multiplexed microfluidics, and mixer-based microfluidics in the manipulation of liquid movement, mixing, and splitting. These methodologies leverage the physical properties of liquids, such as capillary forces and dielectric forces, to achieve precise control over fluid dynamics. SlipChip technology, which branches into rotational SlipChip and translational SlipChip, controls fluid through sliding motion of the microchannel. On the other hand, innovative designs in microfluidic systems pursue better modularity, reconfigurability and ease of assembly. Different assembly strategies, from one-dimensional assembly blocks and two-dimensional Lego®-style blocks to three-dimensional reconfigurable modules, aim to enhance flexibility and accessibility. These technologies enhance user-friendliness and accessibility by offering integrated control systems, making them potentially usable outside of specialized technical labs. Microfluidic programmable strategies for channels and flow hold promising applications in biomedical research, chemical analysis and drug screening, providing theoretical and practical guidance for broader utilization in scientific research and practical applications. [ABSTRACT FROM AUTHOR]

Bionic flow fields have been applied in bipolar plates for proton exchange membrane fuel cells (PEMFCs) to significantly improve cell performance. This study, inspired by the vascular structure of plant leaf veins, proposes a bionic flow field that incorporates a sieve plate structure to enhance the distribution of reactants. To evaluate this design, a three-dimensional two-phase isothermal computational fluid dynamics (CFD) model was developed. The effect of hole parameters on the cell performance, such as opening ratio, hole number, and hole arrangement on the bionic sieve plate (BSP), was investigated and compared with a parallel flow field (PFF). The results showed that the peak power density of the bionic sieve plate flow field (BSPFF) was 0.991 W/cm2, 25.4% higher than that of the PFF, when the ratio of openings was 22.3%, the number of openings was 4, the sieve angle was 22.5°, and the number of sieves was 5. This BSPFF design provides insight into the development of bipolar plates to improve the performance of PEMFCs. [Display omitted] • Bionic sieve plate flow field (BSPFF) was proposed for bipolar plates of PEMFC. • Bionic sieve plate flow channel(BSPFC) was investigated firstly via four strategies. • The introduction of BSP changes the gas mass transfer to convection and diffusion. • The peak power density of BSPFC exceeds that of CSC by a significant 5.33%. • 5-BSPFF's peak power density surpasses PFF's by an impressive 25.4%. [ABSTRACT FROM AUTHOR]

We investigate the influence of vortices remote from the boundary on the near-wall flow dynamics in wall-bounded flows. A vortex ring with precisely controlled local twist is introduced into the outer layer of a channel flow at a moderate Reynolds number. We find that the minimum vorticity flux for triggering the transition to turbulence is significantly reduced from the initial disturbance of an untwisted vortex ring to that of a twisted ring. In particular, the latter disturbance can cause vortex bursting in the early transitional stage. The impact of vortex bursting on the transition process is characterised by the near-wall, wall-normal velocity with the rapid distortion theory. The wall-normal velocity grows during vortex bursting, and leads to streak formation and then the transition to turbulence. The notable wall-normal velocity is induced by the large di-vorticity generated in vortex bursting. We model the growing radial component of the di-vorticity in terms of the local twist, and demonstrate that its surge is due to the generation of highly twisted vortex lines in vortex bursting. Then, we derive that the generation of the di-vorticity in the outer layer enhances the wall-normal velocity in the inner layer via the Poisson equation with the image method and the multipole expansion. Thus, we elucidate that the vortex bursting can have an effect on the transition process. [ABSTRACT FROM AUTHOR]

Snap-through is a buckling instability that allows slender objects, including those in plant and biological systems, to generate rapid motion that would be impossible if they were to use their internal forces exclusively. In microfluidic devices, such as micromechanical switches and pumps, this phenomenon has practical applications for manipulating fluids at small scales. The onset of this elastic instability often drives the surrounding fluid into motion – a process known as snap-induced flow. To analyse the complex dynamics resulting from the interaction between a sheet and a fluid, we develop a prototypical model of a thin sheet that is compressed between the two sides of a closed channel filled with an inviscid fluid. At first, the sheet bends towards the upstream direction and the system is at rest. However, once the pressure difference in the channel exceeds a critical value, the sheet snaps to the opposite side and drives the fluid dynamics. We formulate an analytical model that combines the elasticity of thin sheets with the hydrodynamics of inviscid fluids to explore how external pressure differences, material properties and geometric factors influence the system's behaviour. To analyse the early stages of the evolution, we perform a linear stability analysis and obtain the growth rate and the critical pressure difference for the onset of the instability. A weakly nonlinear analysis suggests that the system can exhibit a pressure spike in the vicinity of the inverted configuration. [ABSTRACT FROM AUTHOR]

During the 2018 K $\unicode{x012B}$ lauea lower East Rift Zone eruption, lava from 24 fissures inundated more than 8000 acres of land, destroying more than 700 structures over three months. Eruptive activity eventually focused at a single vent characterized by a continuously fed lava pond that was drained by a narrow spillway into a much wider, slower channelized flow. The spillway exhibited intervals of 'pulsing' behaviour in which the lava depth and velocity were observed to oscillate on time scales of several minutes. At the time, this was attributed to variations in vesiculation originating at depth. Here, we construct a toy fluid dynamical model of the pond–spillway system, and present an alternative hypothesis in which pulsing is generated at the surface, within this system. We posit that the appearance of pulsing is due to a supercritical Hopf bifurcation driven by an increase in the Reynolds number. Asymptotics for the limit cycle near the bifurcation point are derived with averaging methods and compare favourably with the cycle periodicity. Because oscillations in the pond were not observable directly due to the elevation of the cone rim and an obscuring volcanic plume, we model the observations using a spatially averaged Saint-Venant model of the spillway forced by the pond oscillator. The predicted spillway cycle periodicity and waveforms compare favourably with observations made during the eruption. The unusually well-documented nature of this eruption enables estimation of the viscosity of the erupting lava. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is widely recognized as a key technology for enhancing coalbed methane production. The fracturing fluid has physicochemical reactions with the coal fractures, along with their duration, critically affecting fracture permeability, thereby determining the effectiveness of the technology. However, the study has not received enough attention. In this study, coal fracture seepage tests were carried out using in situ continuous injection of fracturing fluid. The seepage evolution of viscoelastic surfactant fracturing fluid (VESFF) was investigated at different times (0, 1, 2, 3, 4, and 5 days), and de-ionized water (DW) and potassium chloride solution (KCL) were used for comparison. The results showed that the flow rate increased compared to initial flow rate after VESFF treatment for two to four days, while the flow rate could not be recovered after DW and KCL treatment. The optimal treatment duration for VESFF was two days: marked by a sevenfold increase in the flow rate, an 84% increase in initial hydraulic aperture, and minimal momentum loss. After two more days of VESFF treatment, the pressure gradient and effective confining pressure became greater than 6 MPa/m and 3.5 MPa, respectively, and showed a significant excessive discharge characteristics (β < 0), which resulted from the generation and dilation of microcracks, increasing the number of flow channels due to coupled fluid–mechanical behavior. The degree of flow nonlinearity decreased with increasing VESFF treatment duration and increased with increasing effective confining pressure. These results have profound implications for optimal treatment duration and mechanism of VESFF strengthening coal fracture seepage. [ABSTRACT FROM AUTHOR]

Fluid elastic instability (FEI) is widely regarded as the most destructive mechanism of flow-induced vibration. Numerous failures of heat exchanger tubes have been attributed to this phenomenon. This paper focuses on a normal triangular tube array and develops a semi-analytical time-domain solving model to address FEI in the streamwise direction. Utilizing computational fluid dynamics simulations and image processing techniques, a comprehensive set of tube-in-channel model parameters is derived, including the area perturbation amplitude, phase difference, mean area along the flow channel, and steady-state term of flow velocity. Tube motion in the streamwise direction generates a disturbance distinct from that caused by transverse flow, leading to revisions in the expressions of relevant model parameters. Furthermore, variations in these parameters across different positions and velocities are quantitatively analyzed through function fitting, yielding specific mathematical formulas. Ultimately, the derived tube-in-channel model parameters applicable to streamwise FEI are validated against experimental data, affirming the model's accuracy. [ABSTRACT FROM AUTHOR]

Harmonic oscillations of the walls of a turbulent plane channel flow laden with inertial particles are studied by point-particle direct numerical simulation to improve our understanding of the physical mechanism for friction drag reduction. We specify a high wall oscillation amplitude and choose particle parameters that feature a considerable drag-reduction effect. The particle effect on the drag modulation is investigated by varying the wall oscillation period ( T + ) across a wide range. We find that particles enhance drag reduction for T + ≤ 30 while attenuating it for T + > 30. Specifically, we observe drag increase near the optimal oscillation period, i.e., T + = 50 and 75. To explore the coupling mechanism of drag modulation by particles and spanwise wall oscillations, we examine the modifications of turbulence and particle statistics. Moreover, the self-sustaining cycle of near-wall turbulence is modulated by wall oscillations and/or particles. We find that the quasi-streamwise vortices are tilted and weakened by wall oscillations while significantly depopulated by particles. The modulated turbulence also affects the near-wall particle accumulation and clustering patterns, which results in different fluid–particle interactions compared with the non-actuated particle-laden channel flow. The mechanism of drag modulation is governed by the competition between reduced fluid Reynolds shear stress and particle stress. To give a quantitative view of the drag modulation, we compare the contributions of different stress components to the friction drag coefficient. Although the fluid Reynolds shear stress is reduced by particles, which corresponds to reduced turbulent kinetic energy production, the particle stress contribution remains significant, especially for the drag-increase case. Furthermore, the anisotropy invariant maps are provided, which show a striking resemblance of increased near-wall turbulence anisotropy as observed in other drag-reduced flows. This suggests that the constraint of increased turbulence anisotropy might be only a necessary but not sufficient condition for achieving drag reduction since this constraint is satisfied in our drag-increase case. [ABSTRACT FROM AUTHOR]

In this study, we proposed an efficient approach based on a deep learning (DL) denoising autoencoder (DAE) model for denoising noisy flow fields. The DAE operates on a self-learning principle and does not require clean data as training labels. Furthermore, investigations into the denoising mechanism of the DAE revealed that its bottleneck structure with a compact latent space enhances denoising efficacy. Meanwhile, we also developed a deep multiscale DAE for denoising turbulent flow fields. Furthermore, we used conventional noise filters to denoise the flow fields and performed a comparative analysis with the results from the DL method. The effectiveness of the proposed DL models was evaluated using direct numerical simulation data of laminar flow around a square cylinder and turbulent channel flow data at various Reynolds numbers. For every case, synthetic noise was augmented in the data. A separate experiment used particle-image velocimetry data of laminar flow around a square cylinder containing real noise to test DAE denoising performance. Instantaneous contours and flow statistical results were used to verify the alignment between the denoised data and ground truth. The findings confirmed that the proposed method could effectively denoise noisy flow data, including turbulent flow scenarios. Furthermore, the proposed method exhibited excellent generalization, efficiently denoising noise with various types and intensities. [ABSTRACT FROM AUTHOR]

In this study, the wall shear stress in the channel flow of polyacrylamide polymers was investigated through electrochemical experiments, and the effects of the polymer concentration were evaluated at different Reynolds numbers. The objective was to explore the relationship between the changes in the drag reduction and near-wall turbulence structure induced by the polymer. The experiments were conducted using polymer concentrations of 0, 20, 50, 100, and 150 ppm, and a drag reduction of approximately 23% was achieved at a bulk Reynolds number of R e b = 18 750. In the electrochemical method, the working electrode was arranged spanwise, and simultaneous measurements were performed for eight electrodes to discuss the scale of the near-wall low-speed streaks and burst events. A comprehensive analysis of the correlation of the wall shear stress in the streamwise direction and the cross-spectrum of two points in the spanwise direction revealed that large streamwise and spanwise scales of near-wall low-speed streaks were generated at high polymer concentrations. Furthermore, the results obtained using the variable interval time averaging technique indicated that polymer incorporation suppressed the wall shear stress fluctuations and weakened both the intensity and frequency of the bursting events. [ABSTRACT FROM AUTHOR]

In this work, a novel eddy viscosity enhanced temporal direct deconvolution model (TDDM) is proposed for temporal large-eddy simulation (TLES) of turbulent channel flow at large filter widths. To improve the accuracy of the constant eddy viscosity (CEV) model, particularly in the near-wall region, a damping function is incorporated to refine its performance. Moreover, a spatial filtering strategy is introduced to reduce the aliasing errors associated with the computation of subfilter-scale (SFS) stress, thereby enhancing numerical stability. In the a posteriori study, the accuracy of the CEV model is assessed comprehensively by comparing the TLES results with corresponding temporally filtered direct numerical simulation data. The results demonstrate that the CEV-enhanced TDDM provides accurate predictions across various statistical properties of velocity, instantaneous flow structures, kinetic energy spectra, and SFS energy fluxes. The coefficient sensitivity analysis of the CEV model reveals that the model coefficient significantly influences low Reynolds number flows, while its impact on high Reynolds number flows is relatively small. TLES on coarse grids demonstrate that the CEV-enhanced TDDM exhibits strong robustness and accuracy at different grid resolutions. Additionally, the CEV-enhanced TDDM in high Reynolds number flows is stable and accurate at remarkably large filter widths. [ABSTRACT FROM AUTHOR]

This study numerically investigates the impact of micro-blowing/suction parameters on the flow and heat transfer characteristics. Different models and parameters are evaluated by energy saving rate and comprehensive performance coefficients. The numerical results indicate that micro-blowing reduces the wall friction drag, while micro-suction increases the wall friction, and the magnitude of drag reduction (or drag increase) increases with the augment of the micro-blowing/suction coefficient. The maximum drag reduction rates of the three models are 2.60%, 3.59%, and 3.83%, respectively. When micro-blowing and micro-suction are arranged at the bottom and top of the channel, respectively, or both arranged at the bottom of the channel, the Nusselt number increases by at least 69.75% and 89.45%, respectively. The arrangement of micro-blowing and micro-suction both arranged at the bottom of the channel is optimal for heat transfer and drag reduction. In addition, with the present three arrangements, energy saving in the channel flow can be achieved. [ABSTRACT FROM AUTHOR]

To enhance the overall performance of regenerative flow pump (RFP) to achieve efficient and stable operation over a broad range, this paper employs numerical simulation to study the internal flow conditions of RFP models with three different inclination coefficients (Ic = −0.25, Ic = 0, Ic = 0.25). The analysis focuses on the pressure distribution, energy exchange, velocity variation, and vorticity distribution characteristics within the impeller and channel. The comparison indicates that at Ic = −0.25 with an outward channel, the flow within the pump is stabilized, and the rate of pressure growth and exchange intensity are increased. When Ic = 0 with a semi-circular channel and Ic = 0.25 with an inward channel, there are narrower flow space at the channel's outer diameter, impeding effective fluid motion along the channel and inducing chaotic flow. This condition escalates flow losses and adversely affects the hydraulic performance of the RFP. Additionally, the analysis based on the vorticity transport equation reveals that the Coriolis force term significantly contributes to the generation and transport of vortex in the impeller, while the vortex stretching term dominates the transport of vortex in the channel. [ABSTRACT FROM AUTHOR]

Over the past decade, the integration of artificial neural networks (ANNs) has garnered significant interest, capitalizing on their ability to discern intricate patterns within data. Focused on enhancing computational efficiency, this article explores the application of ANNs in forecasting fluid-dynamics simulations, particularly for the benchmark problem of fluid flow in a two-dimensional (2D) channel. Leveraging a multilayer perceptron trained on finite volume method numerical data, for both interpolation and extrapolation estimations and various grid resolutions, our findings demonstrate the ANN's prowess as a swift and accurate surrogate for traditional numerical methods. Overall, the results of this work mark a pioneering step toward leveraging machine learning for modeling complex relationships in fluids phenomena, promising transformative advancements in computational fluid dynamics. [ABSTRACT FROM AUTHOR]

This study is based on two objective functions: minimizing heat transfer entropy production and minimizing viscous dissipation. The reverse-temperature equation and volumetric force sources are derived using variational methods for optimizing convective heat transfer in two-dimensional flows. Linear weights are adjusted to generate velocity and temperature fields corresponding to different performance metrics. The research demonstrates that the flow patterns determined through optimization effectively characterize optimal heat transfer performance under varying flow power consumption. Furthermore, compared to non-optimized flows, linear weights induce transitions in velocity and temperature fields from mild to highly perturbed states. Additionally, addressing the reverse-temperature equation with a negative diffusion coefficient that is challenging for traditional numerical methods, we utilize a physics-informed neural network strategy for solution. This approach significantly reduces the required grid resolution. The findings of this study can be applied to design passive techniques enhancing wall-to-fluid heat transfer and provide a novel approach for solving systems of mixed conventional and non-classical partial differential equations. [ABSTRACT FROM AUTHOR]

Supercritical CO2 fracturing technology has shown great potential for enhancing production in unconventional reservoirs. It is essential to clarify the transport mechanism of proppant under the dynamic propagation conditions within rough fractures. A realistic rough fracture model is reconstructed, and Computational Fluid Dynamics simulations are conducted to track proppant movement during fracture propagation. The typical transport characteristics of proppant within rough fractures are revealed, and the effects of fracture propagation rate, proppant density, mass flow rate, particle size, sand ratio, and temperature on the support effect are discussed. The results show that the flow channels formed by sand carrying fluid in rough fractures are complex, with fracture propagation changing some flow channels. The proppant forms an irregular sand bed interspersed with unfilled areas, and complex flow characteristics are generated. The increase in fractal dimension increases the resistance in the fluid flow process and affects the movement of the proppant, which tends to create unfilled areas. Low density and size of proppant can improve the proppant placement length. In a certain temperature range, high temperature injection of sand carrying fluid can improve the proppant placement effect. In addition, the low sand ratio and high mass flow rate pumping can be used to form the dominant channel, followed by pumping with a high sand ratio and low mass flow rate for effective support. [ABSTRACT FROM AUTHOR]

As an important technique for manipulating particles in fluid–solid channel flows, inertial focusing encourages the design of the channel geometry to enhance particle radial aggregation. Traditional methods typically use exquisite sheathes or elbows to create constricted flows, which ultimately increase flow resistance and lower fluid–solid separation efficiency. This paper presents a slippery wall modification technique that, by regulating the channel flows, is expected to induce nontrivial particle lateral migrations. More specifically, interface-resolved simulations are performed using the lattice Boltzmann method. A slip boundary condition is applied to the redesigned hydrophobic bottom wall. It is observed that the typical bifurcate migration, i.e., particles moving divergently toward the upper and lower equilibrium positions around a crucial location (CL), does not occur along the channel centerline. The CL is always below the centerline, and it decreases consistently with an increase in Kn or Re. By increasing Re, particles are prone to approach the channel centerline. With larger Kn, particles in the higher equilibrium position are affected in the same way, but their lower counterparts are drawn to the bottom wall. [ABSTRACT FROM AUTHOR]