Converging Flow Field Research Articles

An easy-to-use analytical model for standing column wells operating with bleed

Accurate assessment of subsurface heat transport is vital for the design of standing column well systems. When bleed is utilized, the mathematical problem is governed by coupled heat transfer and groundwater flow within a radially convergent flow field, making the development of models challenging. While numerical models exist to simulate these transient processes, the absence of simple and accessible analytical solutions limits their broader application. This study addresses this gap by developing a novel easy-to-use analytical model to accurately represent the heat advection–diffusion problem in standing column wells operating with bleed. The proposed model combines the well-known infinite line source model with an innovative scaling function, inspired from the field of solute transport, through a simple convolution product. Notably, the developed model depends on only three dimensionless parameters: dimensionless advection time, Péclet number, and bleed ratio. Rigorous validation against two distinct sets of reference numerical solutions demonstrated the model’s efficiency, accuracy, and reliability across a broad spectrum of nine physical parameters. Key results include relative root mean square errors on the order of 10−3 across 200 reference solutions, confirming the model’s robustness. These findings highlight the model’s potential to significantly advance both research and practical applications in the design and optimization of standing column wells.

Modeling Sediment Fluxes From Debris‐Rich Basal Ice Layers

AbstractSediment erosion, transport, and deposition by glaciers and ice sheets play crucial roles in shaping landscapes, provide important nutrients to downstream ecosystems, and preserve key indicators of past climate conditions in the geologic record. While previous work has quantified sediment fluxes from subglacial meltwater, we also observe sediment entrained within basal ice, transported by the flow of the glacier itself. However, the formation and evolution of these debris‐rich ice layers remains poorly understood and rarely represented in landscape evolution models. Here, we identify a characteristic sequence of basal ice layers at Mendenhall Glacier, Alaska. We develop a numerical model of frozen fringe and regelation processes that describes the co‐evolution of this sequence and explore the sensitivity of the model to key properties of the subglacial sedimentary system, using the Instructed Glacier Model to parameterize ice dynamics. Then, we run numerical simulations over the spatial extent of Mendenhall Glacier, showing that the sediment transport model can predict the observed basal ice stratigraphy at the glacier's terminus. From the model results, we estimate basal ice layers transport between 23,300 and 39,800 of sediment, mostly entrained in the lowermost ice layers nearest to the bed, maximized by high effective pressures and slow, convergent flow fields. Overall, our results highlight the role of basal sediment entrainment in delivering eroded material to the glacier terminus and indicate that this process should not be ignored in broader models of landscape evolution.

Heat Flux Prediction of Radiation Balance Wall by Deep Convolutional Neural Networks

Aerodynamic thermal prediction plays a crucial role in the design of a hypersonic vehicle, particularly with regard to the thermal protection system. Traditional methods of aerodynamic thermal prediction encounter several primary challenges, including slow convergence rates, rigorous computational grid requirements, and the need to simplify by assuming isothermal wall conditions. In this research, we propose using the Convolutional Neural Network (CNN) Hybrid Feature (HF) model to facilitate rapid aerothermal predictions for both isothermal wall conditions with varying wall temperatures and radiation balance wall conditions. The CNN HF model is trained separately for isothermal wall conditions under identical inflow conditions as well as for diverse inflow conditions and radiation balance wall temperature scenarios. The model’s predictions are then compared to numerical simulation results. Our findings demonstrate that the CNN HF model efficiently provides rapid aerothermal predictions by leveraging macroscopic converged flowfield data. In the majority of cases, the model achieves a threefold enhancement in computational efficiency while maintaining predictive accuracy within a 5% range when compared to numerical simulation results. The application of the CNN HF approach in aerothermal prediction for different wall temperatures and radiation balance scenarios has significantly reduced the time required to obtain aerodynamic heating results.

Numerical investigations of the restriction effects on a ship navigating in pack-ice channel

This paper adopts Computational Fluid Dynamics (CFD) method and Discrete Element Method (DEM) to simulate a ship navigating in pack-ice channel considering the effects of channel restriction. First, from the simulations of the ship sailing in open-water channel by CFD, it is found that the effects of channel width on water resistance is more pronounced than the impacts by level-ice thickness. Then, based on the stable and converged flow field obtained by CFD simulations, the CFD-DEM coupling method is applied to reveal the effects of channel width and level ice thickness on ship-ice-water interactions and ice resistances at different ship speeds. The results indicate that as the channel width decreases, the accumulation of pack ice in the areas of bow and midship intensifies. The ice resistances on the bow and midship increase notably, and the lateral ice forces exhibit pronounced asymmetric and random characteristics. In extremely narrow pack-ice channels, lower ship speed results in lager ice resistance and lateral ice force on the ship. In addition, as the level ice thickness decreases, the pack ice is more easily squeezed below the level ice, resulting in the decreases of ice resistance and lateral ice force.

Computational Thermal Analysis of Divergent and Convergent Flow Channels for Cooling Plates in PEM Fuel Cells

During the operation of polymer electrolyte membrane fuel cells excess heat is generated as a result of electrochemical reactions. This heat raises the temperature of the polymer electrolyte membrane fuel cells, which can damage the membrane. Homogeneity of the temperature through the fuel cell is important in terms of stability and performance. Thermal management is therefore essential and is provided by the cooling channels formed on the bipolar plates or cooling plates. In this paper, a three-dimensional computational analysis of the cooling plate with divergent and convergent flow field designs is carried out. In this context, heat transfer and fluid flow performances of these two different flow fields are considered in terms of temperature uniformity, maximum temperature and pressure drop. Numerical results demonstrated that the more uniform temperature distribution along the fuel cell could be achieved with divergent flow field design. Furthermore, when a divergent design is used, the maximum surface temperature of the cooling plate and the pressure drop between the inlet and outlet of the channel are reduced.

Fracture connectivity and flow path tortuosity elucidated from advective transport to a pumping well in complex 3D networks

Conservative, non-sorbing particle arrivals to a pumping well are used to provide high-resolution data to explore network connectivity and flow path tortuosity as a function of scale for a series of complex 3D discrete fracture networks (DFNs). The DFNs are stochastically generated using orientations ranging from random to three orthogonal planes, power-law distributions of length, and a broad range of density ranging from sparse to moderately dense networks. The internal architecture of the DFNs is intensively sampled by distributing conservative particles evenly over all fractures within a large spherical release volume. A non-directional framework featuring a radially convergent flow field, established by applying a weak sink in the center of the model domain and assigning equal-value constant head boundaries to all sides of the model domain, is used to minimize directional dependence on network connectivity. Results indicate particle velocity is significantly influenced by fracture set orientation in the degree to which fracture sets promote fracture connectivity, and that broad distributions of ensemble velocity can arise from networks with constant fracture transmissivity where slower velocities are characteristic of particle placement into fracture elements less connected to the sink, and vice versa. Inverse particle velocity is strongly power-law for all networks tested and indicates persistent and diverse retention characteristics. The degree of retention decreases in the transition from poorly- to well-connected networks and with increasing distance of particle release due to the availability of more fracture pathways with stronger connection to the sink. Tortuosity is exponentially distributed for all networks tested with median values that stabilize over a distance approximately 10 times the minimum fracture length, and is most sensitive to fracture length, followed by orientation and density.

Convergent radial transport in three-dimensional heterogeneous aquifers: The impact of the hydraulic conductivity structure

This paper studies the impact of the hydraulic conductivity structure on solute transport in a radially convergent heterogeneous flow field, which is generated by a well pumping a confined aquifer. The solute is injected instantaneously in a fully penetrating well at a known distance from the pumping well and the analysis is performed numerically by considering four conductivity structures sharing the same two-point statistics, but displaying widely different higher-order moments and connectivity features. The overall objective of the present work is to assess the impact of three-dimensional hydraulic conductivity structures on the Breakthrough Curve (BTC) at a pumping well as a function of a few structural parameters: the logconductivity variance the integral scales along the horizontal and vertical directions, the local-scale dispersivity and the distance of the injection well. The numerical simulations are also compared with two analytical solutions from literature based on the First Order Approximation and the Self Consistent Approximation, respectively. The results indicate that the principal features of the BTC are weakly dependent on the hydraulic conductivity structure, similar to the findings of Janković (2017) for transport in uniform flow. Also, the simple First-Order solution provides a good approximation of the BTC in most of the scenarios considered, and thus it can be a useful and effective tool for screening purposes in applications dealing with aquifers’ contamination.

Tracer test analysis using flow and transport simulation code and new analytical transport model 27 April 2019.

A convergent flow field tracer test, in two phases, with injection of sodium chloride solution, was conducted on a pumping well and neighboring piezometers belonging to the Kovin-Dubovac area drainage system, on the Serbian sector of the Danube River. The initial goal was to determine the values of hydrogeological parameters in order to analyze the results of the subsequent experiments involving injection of the selected solutes. SEAWAT code (through the Visual Modflow™ 2011 interface), as well as the newly developed analytical model for multilayer setting (1D transport solution for tracer injected as a Dirac impulse in a radial convergent flow field), was used to develop and calibrate a model of the studied portion of the aquifer. The new analytical model demonstrated a very good match to the measured values and to the results of numerical simulation, which indicates that it can be of great utility in characterizing transport conditions. PRACTITIONER POINTS: Results confirm the conclusions of research papers on tracer tests that 10-m scale tests regularly point to heterogeneous aquifer. New analytical 1D radial transport model for multilayer setting demonstrated a very good match with numerical simulation and experimental data. Developed analytical model is usable for characterizing transport conditions in a radial convergent multilayer flow field or other settings.

A Method of Accelerating the Convergence of Computational Fluid Dynamics for Micro-Siting Wind Mapping

To assess wind resources, a number of simulations should be performed by wind direction, wind speed, and atmospheric stability bins to conduct micro-siting using computational fluid dynamics (CFD). This study proposes a method of accelerating CFD convergence by generating initial conditions that are closer to the converged solution. In addition, the study proposes the ‘mirrored initial condition’ (IC) using the symmetry of wind direction and geography, the ‘composed IC’ using the vector composition principle, and the ‘shifted IC’ which assumes that the wind speed vectors are similar in conditions characterized by minute differences in wind direction as the well-posed initial conditions. They provided a significantly closer approximation to the converged flow field than did the conventional initial condition, which simply assumed a homogenous atmospheric boundary layer over the entire simulation domain. The results of this study show that the computation time taken for micro-siting can be shortened by around 35% when conducting CFD with 16 wind direction sectors by mixing the conventional and the proposed ICs properly.

Transport phenomena of convergent and divergent serpentine flow fields for PEMFC

Reactive species and water transport are crucial for the proton exchange membrane fuel cell operation and performance, and for this, effective flow field design can facilitate the desired transport characteristics of species. From this motivation, the conventional single serpentine flow field pattern is modified by convergent and divergent design concepts and the complex transport phenomena of the newly developed flow field designs are investigated by a numerical approach. For the numerical analyses, an experimentally validated mathematical model is developed to predict the current density, oxygen mass transport, water concentration and pressure distribution. The different configurations of modified convergent and divergent serpentine flow fields are then numerically solved and the results are compared with the conventional serpentine flow field pattern. The transport of reactive species and water concentration are analyzed from the different perspectives including cathode domains and surfaces with a quantitative formulation of the transport species. The numerical results reveals that the modified convergent serpentine flow fields yield to a uniform current density due to the lower mass fraction of water concentration over the reaction zone facilitating better oxygen mass transport and also higher channel pressure distribution along the flow field comparing the conventional and divergent type serpentine flow fields.

Numerical Investigation of Convergent and Divergent Parallel Flow Fields for PEMFCs

AbstractIn this study, the classical parallel flow field pattern is modified by a convergent and divergent design concept for proton exchange membrane fuel cells (PEMFCs). The modification is achieved by varying the channel depth with different constant inclination gradients from the inlet to the outlet, along with the bipolar plate width which creates either a convergent or divergent flow field depending on the position of the inlet and outlet selected. The numerical model is solved to predict the cell performance including the mass transport, water vapor concentration and, pressure and current density distribution for the flow fields. The numerical results reveal that the modified convergent parallel flow fields have a better mass transport and water removal characteristics than those in the conventional one, whereas mal‐distribution of species and excessive water concentration occur in the conventional and divergent parallel flow fields. Introducing convergent parallel flow field design concept not only minimizes these issues but the cell power density is also improved by a maximum of 16%, which can show a new window in PEMFC flow field design concept.

Novel convergent-divergent serpentine flow fields effect on PEM fuel cell performance

A new design of convergent and divergent flow fields are being developed in single serpentine flow field pattern for proton exchange membrane (PEM) fuel cell. The channel depth is varied by means of inclination from inlet to outlet of the bipolar plate. By the varying inclined channel depth, it created convergent/divergent flow effect along the channel length in the single serpentine. Four different convergent flow fields are manufactured by the varying inclined channel depth from inlet to outlet as 1.5 mm–0.5 mm, 2.5 mm–1.5 mm, 3 mm∼1 mm and 3.5 mm–0.5 mm, which are divergent flow fields as well by interchanging between inlet and outlet section. These convergent and divergent flow fields are compared with two conventional single serpentine having 1 mm and 2 mm constant channel depth for an active area of 4.7 cm2. The experimental results showed that both convergent and divergent flow fields outperforms the conventional serpentine flow fields where maximum performance was achieved from convergent flow field C1 (1.5 mm–0.5 mm) improving 19–27% power than two conventional serpentine flow fields. Therefore this novel convergent serpentine flow field effect can improve PEM fuel cell performance by its suitable bipolar plate design.

Size-based separation of supercoiled plasmid DNA using ultrafiltration

HypothesisMost previous studies of membrane-based separations have shown no effect of DNA size on plasmid transmission through small pore size ultrafiltration membranes, consistent with the predicted behavior for flexible polymer chains. However, supercoiled plasmids are known to have a highly “branched” structure with the number of branches dependent on the DNA length. This difference in branching could lead to a significant dependence of the transmission on the plasmid size, providing opportunities for size-based separations using ultrafiltration. ExperimentsData were obtained with 3.0, 9.8, and 16.8kbp plasmids using both cellulosic and polyethersulfone ultrafiltration membranes with different nominal molecular weight cutoffs. Initial experiments were performed with purified samples of the supercoiled and linear isoforms, with the results used to identify appropriate conditions for plasmid separation. FindingsPlasmid transmission increased with increasing filtrate flux due to elongation of the plasmids in the converging flow field. However, the flux dependence was different for each plasmid due to differences in the extent of branching of the twisted supercoiled DNA. This behavior provided a significant selectivity that could be used to separate the 3.0 and 16.8kbp supercoiled plasmids using small pore size ultrafiltration membranes.

Enhanced purification of plasmid DNA isoforms by exploiting ionic strength effects during ultrafiltration.

The solution structure of plasmid DNA is known to be a strong function of solution conditions due to intramolecular electrostatic interactions between the charged phosphate groups along the DNA backbone. The objective of this work was to determine whether it was possible to enhance the use of ultrafiltration for separation of different plasmid isoforms by proper selection of the solution ionic strength and ion type. Experiments were performed with a 3.0 kbp plasmid using composite regenerated cellulose ultrafiltration membranes. The transmission of the linear isoform was nearly independent of solution ionic strength, but increased significantly with increasing filtrate flux due to the elongation of the highly flexible plasmid in the converging flow field into the membrane pores. In contrast, the transmission of the open-circular and supercoiled plasmids both increased with increasing NaCl or MgCl2 concentration due to the change in plasmid size and conformational flexibility. The effect of ionic strength was greatest for the supercoiled plasmid, providing opportunities for enhanced purification of this therapeutically active isoform. This behavior was confirmed using experiments performed with binary mixtures of the different isoforms. These results clearly demonstrate the potential for enhancing the performance of membrane systems for plasmid DNA separations by proper selection of the ionic conditions.

Heat Transfer from Slip Spheres to a Shear-Thickening Fluid: Effects of Slip Velocity and Particle Volume Fraction

Numerical simulations are performed to study the effects of tangential slip velocity and volume fraction of slip spheres on the heat transfer characteristics of assemblages of slip spheres to a shear-thickening fluid of n = 1.4. Navier's linear slip velocity boundary condition is applied at the fluid-solid interface and free surface cell model is used to estimate the effects of the adjacent particles. The governing equations are solved using a segregated approach. First continuity and momentum equations are numerically solved using a finite difference method based simplified marker and cell (SMAC) semi-implicit algorithm implemented on a staggered grid arrangement in spherical coordinates. To solve energy equation fully converged flow field is used as input. The present numerical solver is validated by comparison of present literature results with the existing literature values. Further new results obtained in the range of conditions as Reynolds number, Re: 0.1 – 200; Prandtl number, Pr: 1 – 100; volume fraction of slip spheres, Φ: 0.1 – 0.5 and a dimensionless slip parameter, λ: 0.01 – 100. Finally influence of these pertinent dimensionless parameters on isotherm contours and surface and average Nusselt numbers are thoroughly delineated.

Study of the Spatial Distribution of Burning Particles in a Pyrotechnic Flame Based on Particle Velocity

The burning particles in the pyrotechnic flame play an important role in the ignition and spectral radiance of the pyrotechnic. We used particle image velocimetry (PIV) and high-speed camera (HSC) photography to investigate the 3D spatial pattern and velocity of the burning particles in the flame of pyrotechnics. The original images captured by the HSC were preprocessed through threshold selection, image bivalency, edge detection, and contour extraction and segmentation to obtain the particle coordinates and velocity. Consequently, the particle tracking model was established and the velocity and spatial distribution of the burning particles were obtained. A comparison of the flame flow field with particle image velocimetry demonstrated the typical characteristics of the two-phase flow of the pyrotechnic flame between burning particles and gas. Compared with the convergent gas flow field, the higher velocity burning particles had a discrete distribution in the “comet tail” shape region and showed the same direction of motion as the flame flow field, whereas the lower velocity burning particles had larger outlying regions and showed inconsistent directions of motion. The flow field of the burning particles was more chaotic than the flame flow field of the burning pyrotechnics.

Analysis of Mechanical Seal Leakage within Hydrostatic on Nuclear Reactor Coolant Pump

According to the fluid hydrodynamic lubrication theory, and the structural characteristics of the convergence gap seal is combined, the effect of differential pressure and centrifugal force should be considered, then the convergent wedge gap mechanical seals flow field numerical model is established and the influence of the leakage factors are researched, including the geometric parameters and operating parameters. Research has shown that the amount of leakage and the seal clearance were positively correlated. And the larger turning Angle is, the bigger correlation becomes, however, it is negatively correlated with speed and turning radius, the seal leakage is impeded by the centrifugal force and the larger turning radius is, the smaller leakage becomes.

Optimization of Experimental Parameters to Suppress Nozzle Clogging in Inkjet Printing

Stable drop jettability is mandatory for a successful, technical scale inkjet printing, and accordingly, this aspect has attracted much attention in fundamental and applied research. Previous studies were mainly focused on Newtonian fluids or polymer solutions. Here, we have investigated the drop jetting for zinc oxide (ZnO) particulate suspensions. Generally, the inverse Ohnesorge number Z = Oh–1, which relates viscous forces to inertia and surface tension, is sufficient to predict the jettability of single phase fluids. For the inkjet printer setup used here, jetting was possible for Newtonian fluids with 2.5 < Z < 26, but in the identical Z-range, nonjetting and nozzle clogging occurred for certain suspensions. A so-called ring-slit device, which allows for simultaneous formation and detection of aggregates in strongly converging flow fields, and single particle detecting techniques, which allow for an accurate determination of the number and size of micrometer-sized aggregates in suspensions of nanopa...

The impact of extensional viscosity on oil displacement efficiency in polymer flooding

The flow behavior of polymer flooding solution can not only be described simply with shear flow field, but also with convergent and extensional flow field. The extensional viscosity of polymer solutions used in polymer flooding in Daqing Oilfield was investigated with CaBER1 extensional rheometer, and the results showed that the extensional viscosity of which is much higher than shear viscosity with three orders of magnitude. The extensional viscosity of the polymer solutions sharply increased when polymer molecules were stretched to the limit, which means that an extension stiffen phenomenon occurred. The extremely high extensional viscosity and an extension stiffen characteristic in stretching process of polymer solutions could increase capillary number substantially to raise microscopic oil displacement efficiency.

Quantification of aortic regurgitation using proximal isovelocity surface area: an effective segmentation approach based on fuzzy clustering

Echocardiography is mainly to assess valvular regurgitation and get valuable information on the severity of aortic regurgitation (AR). It has several applications, but this paper focuses only on its use in the quantitative evaluation of AR. Proximal isovelocity surface area (PISA) evaluates the severity of AR. The quantification of the effective regurgitant orifice area (EROA) in AR is presented utilising Doppler echocardiography aided by clustering based image segmentation and PISA techniques. Pre-processing is done subjecting the colour Doppler echocardiography image to Gaussian filtering which improves the signal to noise ratio of the image. Subsequently, the image was enhanced with the aid of an image contrast enhancement method that utilises contrast-limited adaptive histogram equalisation. Then this image is segmented by using fuzzy-k means clustering to enable more precise quantification of the AR. PISA method is employed for calculating the quantitative parameters of AR such as, EROA, regurgitant volume (RV), regurgitant fraction (RF), etc. The proximal flow convergence method is used to quantify valvular regurgitation by analysing the converging flow field proximal to the mild, severe or eccentric AR lesion. Experimental evaluation on the commonly accessible dataset illustrates the enhanced performance of the proposed approach effectively.