Velocity Magnitude Distribution Research Articles

Deep neural network-assisted fast and precise simulations of electrolyte flows in redox flow batteries

Flow fields are a key component in redox flow batteries, which is to distribute electrolytes onto electrodes at the maximum uniformity with the minimum pump work. Achieving this design goal requires accurate simulations of electrolyte flows and identification of the dead zones where the flows become weak or stagnant. However, conventional case-by-case numerical simulation requires significant computational resources. In this work, we use deep learning to predict the electrolyte flow in flow batteries with a neural network knows as U-Net. The U-Net is well trained by learning the mapping between the input (flow field geometry) and output (velocity magnitude distribution). Results show that the pixel-wise comparison of the velocity magnitudes between the U-Net-predicted results and finite element simulated results exhibits an average Euclidean distance of 442.6 and an average R2 of 0.979, indicating that the electrolyte distribution can be accurately simulated based on the geometric characteristics of flow fields. In addition, dead zones are precisely identified by labeling the regions with low velocity magnitudes. Modifying the channel depth in these regions substantially enhances the under-rib convection, thereby improving the system efficiency by 5.5 % at 200 mA cm−2. Furthermore, compared to the numerical simulation, the U-Net-assisted prediction significantly reduces the computational time by 99.9 %. It is anticipated that the U-Net-assisted simulation provides an accurate and efficient tool for obtaining the velocity distribution of flow fields that can assist the flow field design especially in large quantities and large scale.

A phenomenological model for dark matter phase-space distribution

ABSTRACT Understanding the nature of dark matter is among the top priorities of modern physics. However, due to its inertness, detecting and studying it directly in terrestrial experiments is extremely challenging. Numerical N-body simulations currently represent the best approach for studying the particle properties and phase-space distribution, assuming the collisionless nature of dark matter. These simulations also address the lack of a satisfactory theory for predicting the universal properties of dark matter haloes, including the density profile and velocity distribution. In this work, we propose a new phenomenological model for the dark matter phase-space distribution. This model aims to provide an Navarro–Frenk–White-like density profile, velocity magnitude distribution, and velocity component distributions that align closely with simulation data. Our model is relevant both for theoretical modelling of dark matter distributions, and for underground detector experiments that rely on the dark matter velocity distribution for experimental analysis.

Integrated Thermodynamic Analysis and Channel Variation Effects on Solid Oxide Electrolysis for Efficient Hydrogen Generation

This study delves into the intricate dynamics of Solid Oxide Electrolysis Cells (SOECs) using comprehensive simulation and analysis. By exploring the effects of temperature, pressure, and geometrical variations, we reveal valuable insights into the behavior of these cells. Our findings encompass diverse aspects, including the distribution of velocity magnitudes, density patterns, and dynamic viscosity within the cell. Notably, varying cell geometries lead to distinct velocity magnitude distributions, shedding light on the fluid dynamics complexities at play. The density distribution analysis underscores the influences of temperature, pressure, and hydrogen concentration on mass transport behavior. Dynamic viscosity profiles further contribute to our understanding of fluid flow characteristics and their relevance to electrochemical reaction rates. Moreover, our study examines the interplay between voltage efficiency, current density, and operating conditions. Intriguingly, we identify scenarios where voltage efficiency surpasses 100%, suggesting potential energy gains from hydrogen production. These intricate relationships emphasize the significance of optimizing SOEC performance for diverse applications. In essence, this research offers a comprehensive view of SOEC behavior, providing insights crucial for enhancing their design and operation. The study's outcomes contribute to the advancement of sustainable hydrogen production through informed decision-making and efficient operational strategies.

Computational design of a smoke detector with high sensitivity considering three-dimensional flow characteristics

Early fire detection is essential for preventing catastrophic events, and fire detectors play a critical role in ensuring fire safety. Among the various types of fire detectors, photoelectric smoke detectors are widely used because of their ability to detect smoke at an early stage. The present study investigates the effects of changes in flow directions and inlet size on the smoke detection ability of a photoelectric smoke detector by conducting computational fluid dynamics (CFD) simulations. The results indicated that when the flow direction changes, the components in the optical chamber may hinder the smoke inflow and increase the detector activation time. Moreover, the smoke inlet size was found to affect the carbon monoxide concentration inside the chamber. The velocity magnitude distributions confirmed the correlation between the smoke velocity in the labyrinth structures entering the optical chamber and the detection ability of the smoke detector. These findings suggested that when optimizing the performance of a smoke detector, flow direction, inlet size, and amount of smoke introduced into the optical chamber should be considered. The current study suggested the modified design of the smoke detector to have superior detection ability in both directions compared to the base case in terms of activation time.

Uncertainty quantification of bank vegetation impacts on the flood flow field in the American River, California, using large‐eddy simulations

AbstractBank vegetation plays a key role in both hydrodynamics and morphodynamics of natural rivers; however, these effects are often unaccounted for in the computational flow dynamics of natural waterways. Recent studies using the large‐eddy simulation (LES), however, have attempted to gain insights into the impacts of bank vegetation on the mean flow field of the natural rivers using a vegetation model, which applies a sink term to the momentum equations of motion. This approach accounts for the effects of the vegetation and provides a practical approach to account for the complex patches of bank vegetation in large‐scale rivers. To implement the vegetation model, a drag coefficient reflecting the overall resistance of vegetal structures to the flow is needed, but due to the lack of calibrated data and range of size, density and type of vegetation, this parameter can be a significant source of uncertainty in the model results. In this study, we use uncertainty quantification (UQ) to investigate the hydrodynamics and bed shear results when a bank vegetation is incorporated in an LES model. To this end, we used the polynomial chaos expansion and Monte Carlo sampling techniques to determine the uncertainties associated with the drag coefficient in the vegetation model and from uncertainties in the bed roughness and inflow discharge. The UQ analysis provided spatially varying confidence levels for the spanwise and vertical distribution of velocity magnitude and for the bed shear stress distributions. In addition, Sobol indices were computed to indicate the relative influence that each parameter had on the overall uncertainty. In general, it was found that uncertainty in flow discharge was the dominant source of uncertainty; however, the drag coefficient in the vegetation model and the bed roughness parameter also made significant contribution to the uncertainty near the banks and bed, respectively.

Bi-global stability analysis on flow separation of two-dimensional compressor cascade

Bi-Global stability analysis (BGSA) is employed to assess the flow separation (FS) in two-dimensional compressor cascades, aiming to investigate the unstable phenomena and underlying mechanisms. The prediction results are correlated with the separation bubble (SPB) on suction surface (SS) or the trailing edge vortex (TEV) and exhibit good agreement with the unsteady numerical simulation (UNS), thereby confirming the instability of these two flow structures. Meanwhile, the prediction results can also partially reflect the initiation of unsteady blade loading. The perturbation distributions obtained from the eigenvectors corresponding to the physically meaningful eigenvalue, reveal two primary unstable regions: one located in the wake region and another coinciding with the SPB. With the increase of incidence angle (IA), the growth rate (GR) of small perturbations transitions from negative to positive, corresponding to the flow state shifting from stable to unstable. Additionally, the inception position of eigenmodes on SS moves upstream until it reaches the leading edge (LE) of the blade. The velocity magnitude distributions in the circumferential direction were further analyzed, demonstrating good agreement with predicted perturbation distributions, and suggesting that the K-H instability mechanism contributes to unstable phenomena. In the analysis of a two-passage flow domain, it is further observed that there exists a time delay in the vortex shedding within the wake, which is not evident at the single-passage condition.

Sustainable Hybrid Design to Ensure Efficiency and Air Quality of Solar Air Conditioning

This research work aims to investigate and subsequently optimize the operating parameters that affect thermal comfort and indoor air quality in the school environment. The proposed design uses a coupling between solar ventilation and the absorption chiller-air conditioning. The heating tower of an adsorption chiller connected to an air conditioning system can be driven by the waste heat from a solar ventilation (exhausted hot air) system thank to this linkage. In order to simulate variables like the velocity magnitude distribution in the air-conditioned room, mathematical modeling is numerically executed. Air temperature evolution along the height of the conditioned room in the mid-length and the air velocity evolution along the length of the conditioned room in the mid-height are studied. According to the numerical simulation results, the inlet air temperature soars as the inlet air velocity rises. Inlet air velocities of 0.05m/s, 0.5m/s, and 1m/s are correlated with inlet air temperatures of 20.7°C, 21.2°C, and 21.3°C, respectively. We conclude that an inlet air velocity in the order of 1m/s (in relation to a maximized air change rate) is in agreement with the general ASHRAE standards for indoor air quality in the case of the school environment, coupled with the essential need to limit as much as possible the spread of viruses.

Numerical study of spray cooling with flash evaporation

This work aims to apply Computational Fluid Dynamic (CFD) method to establish a flash evaporation spray cooling (FESC) model to simulate the heating process and find the optimum cooling performance. The heat transfer process during FESC is studied through numerical simulation using commercial code ANSYS FLUENT. The species transport model and the discrete phase model are applied to simulate the multiphase flow and heat transfer process. The turbulence effect is included. The effects of flow rate, nozzle pressure, nozzle angle, and the nozzle orifice size on spray cooling are investigated through analyzing the final surface temperature distributions. This work revealed the mechanism of the heat transfer process in FESC by means of particle tracks and velocity magnitude distribution. The simulated results for the effect of flow rate were compared with other researchers’ previous published experimental results. The comparison shows same trend, which verified the model and the simulation result. The optimum cooling performance is found by analyzing various working conditions. The results show that high flow rate, high nozzle pressure, small nozzle angle and small nozzle orifice can improve the FESC characteristics. The detailed mechanisms of these effects under various working conditions are also discussed. Under giving working conditions, the optimum cooling performance is obtained for the condition where mass flow rate of working fluid is 2L/min, the nozzle pressure is 100MPa, the nozzle angle is 15 degrees and the orifice size of the nozzle is 1mm.

Relationship between pore fluid velocity distribution and pore size distribution

AbstractThis study investigated the normalized velocity magnitude distribution and normalized pore volume distribution in different porous media with porosity between 13.5% and 85%, including sandstones, carbonates, synthetic silica, sphere packings and fiber scaffolds. It was found that both velocity magnitude and pore size follow the same distribution. These results allow the prediction of the velocity distribution in a porous medium when its pore structure is known or tuning the velocity by controlling the pore structure.

Design of impeller blades for intensification on fluid mixing process in a stirred tank

BackgroundMany studies reported that the nonlinear geometry could create a longer turbulence production region and higher turbulence intensities compared with conventional geometry. The self-similarity impeller based on Hibert curves was introduced to intensify the fluid mixing process in this work. MethodsThe mixing performance of Rushton turbine (RT) impeller and self-similarity impeller were evaluated using experimental analyzes and computational fluid dynamics (CFD) with detached eddy simulation (DES) approach. The chaotic mixing characteristics, mixing time, power consumption, trailing vortices structures, turbulence intensity, turbulent kinetic energy dissipation rate and velocity magnitude distribution were investigated. Significant findingsResults showed that self-similarity impeller can effectively increase the largest Lyapunov exponent (LLE) and multiscale entropy (MSE) of mixing system, shorten the fluid mixing time and decrease the mixing number (η) compared with RT impeller under the constant power consumption, and an improvement was achieved in mixing efficiency with the increase of self-similar iteration number of self-similarity impeller. Meanwhile, the reductions in the power number (Np) of 34.6% with self-similarity 1 impeller and 51.9% with self-similarity 2 impeller were achieved in a wide Re range compared with RT impeller. Two large recirculation zones and trailing vortices were easy to form at the suction side of rectangular impeller blade, which can be destroyed and decomposed into smaller ones through the jet flows produced by the concave-convex structure of self-similarity impeller. In addition, self-similarity impeller can improve the uniformity of fluid turbulence intensity, enhance the turbulent kinetic energy dissipation rate and increase the axial circulation capacity in the stirred tank, and increasingly so with the self-similar iteration number.

Inactivation of B. cereus spores in whole milk and almond milk by serpentine path coiled tube UV-C system: Numerical simulation of flow field, lipid peroxidation and volatiles analysis

A novel continuous thin-film (1.59 mm) serpentine path coiled tube (SPCT) UV system operating at 254 nm wavelength was designed and compared with flow field distribution of whole milk with helical path coiled tube (HPCT) UV system using computational fluid dynamics. The results revealed efficient velocity magnitude distribution at serpentine bend geometric locations of the SPCT UV system. Further in this study, we evaluatedBacillus cereusSpores inactivation in whole milk (WM) and almond milk (AM) using the developed SPCT UV system. Experimental data showed that > 4 log reduction of spores was achieved after six and ten passes of WM and AM at a flow rate of 70 and 162 mL/min, respectively. The bio-dosimetry method was used to verify the delivered reduction equivalent fluence (REF) and reported as 33 ± 0.73 and 36.5 ± 1.9 mJ/cm2. We noticed no significant effect on lipid oxidation and volatiles profile (p > 0.05) up to delivered REF of 60 mJ/cm2. This study demonstrated that high levels of inactivation ofB. cereusspores could be feasible with minimal impact on product quality by UV-C processing of dairy and non-dairy opaque scattering fluids.

A Hydrodynamic–Elastic Numerical Case Study of a Solar Collector with a Double Enclosure Filled with Air and Fe3O4/Water Nanofluid

This work deals with a numerical investigation of a hydrodynamic–elastic problem within the framework of a double enclosure solar collector technological configuration. The solar collector presents two enclosures separated by an elastic absorber wall. The upper enclosure is filled with air, whereas the lower one is filled with Fe3O4/water nanofluid. The mathematical model governing the thermal and flow behaviors of the considered nanofluid is elaborated. The effects of imposed hot temperatures, the Rayleigh number and air pressure on the nanofluid’s temperature contours, velocity magnitude distribution, temperature evolution, velocity magnitude evolution and Nusselt number evolutions are numerically investigated. The numerical results show and assess how the increase in the Rayleigh number affects convective heat transfer at the expense of the conductive one, as well as how much the Nusselt number and the nanofluid velocity magnitude and temperature are affected in a function of the imposed hot temperature type (uniformly or right-triangular distributed on the elastic absorber wall). Moreover, the results evaluate how increases in the air pressure applied on the elastic absorber wall affects the nanofluid’s temperature distribution.

Effect of Impeller’s Blade Number on The Performance of Mixing Flow in Stirred Tank using CFD Simulation Method

The component of an impeller in stirred tank plays an important role in the mixing process for a wide range of industries. The present study conducted the analysis of impeller design specifically on the number of blades to investigate the flow performance in the stirred tank. The analysis was also performed to identify the location of the particle flow dead zone at the bottom of the tank. The grid development and fluid flow study were accomplished using the CFD simulation method via the Ansys Fluent software package. The impeller design with the arrangement of 3,4 and 5 blades number was involved in this study. The rotational speed of the blade was set constant at 90 rpm. The flow characteristic at the vertical position of a tank at 0.01, 0.1, 0.2 and 0.3 m has been investigated. The general governing equation and solution approach used in this simulation were also presented in this paper. The results showed that 5 blades impeller produced a broader region of high-velocity magnitude distribution compared to the 3 and 4 blades. Hence, 5 blades impeller also relatively produced a higher distribution of velocity magnitude compared to the 3 and 4 blades impeller, typically in the upper region of the tank. However, the effect of a number of blades seemed not significant in the region close to the rotating impeller.

Velocity Magnitude Distribution for Flow in Porous Media

Velocity Magnitude Distribution for Flow in Porous Media

A multiscale model for multiple platelet aggregation in shear flow.

We developed a multiscale model for simulating aggregation of multiple, free-flowing platelets in low-intermediate shear viscous flow, in which aggregation is mediated by the interaction of αIIbβ3 receptors on the platelet membrane and fibrinogen (Fg). This multiscale model uses coarse grained molecular dynamics (CGMD) for platelets at the microscales and dissipative particle dynamics (DPD) for the shear flow at the macroscales, employing our hybrid aggregation force field for modeling molecular level receptor ligand bonds. We define an aggregation tensor and use it to quantify the molecular level contact characteristics between platelets in an aggregate. We perform numerical studies under different flow conditions for platelet doublets and triplets and evaluate the contact area, detaching force and minimum distance between different pairs of platelets in an aggregate. We also present the dynamics of applied stress and velocity magnitude distributions on the platelet membrane during aggregation and quantify the increase in stress in the contact region under different flow conditions. Integrating the knowledge from our previously validated models, together with new aggregation scenarios, our model can dynamically quantify aggregation characteristics and map stress and velocity distribution on the platelet membrane which are difficult to measure in vitro, thus providing an insight into mechanotransduction bond formation response of platelets to flow-induced shear stresses. This modeling framework, together with the tensor method for quantifying inter-platelet contact, can be extended to simulate and analyze larger aggregates and their adhesive properties.

Pore-scale velocities in three-dimensional porous materials with trapped immiscible fluid.

We study and document the influence of wetting and nonwetting trapped immiscible fluid on the probability distribution of pore-scale velocities of the flowing fluid phase. We focus on drainage and imbibition processes within a three-dimensional microcomputed tomographic image of a real rock sample. The probability distribution of velocity magnitude displays a heavier tail for trapped nonwetting than wetting fluid. This behavior is a signature of marked changes in the distribution and strength of preferential flow paths promoted by the wettability property of the trapped fluid. When the latter is wetting the host solid matrix, high-velocity areas initially present during single-phase flow conditions are mainly characterized by increased or decreased velocity magnitudes, and the velocity field remains correlated with its counterpart associated with the single-phase case. Otherwise, when the trapped fluid is nonwetting, features that are observed to prevail are appearance and disappearance of high-velocity areas and a velocity field that is less correlated to the one obtained under single-phase conditions.

Velocity and scalar concentrations with low occurrence frequencies within urban canopy regions in a neutrally stable shear flow over simplified urban arrays

The unsteadiness of urban airflow influences rare events of high wind speeds or high scalar concentrations. Therefore, this study uses large-eddy simulations to investigate the geometrical impact of generic block arrays on the statistical features of wind speeds and scalar concentrations within urban canopy regions. Six types of urban-like arrays with uniform and non-uniform block heights are considered, and probability density functions of wind speeds and scalar concentrations are derived based on the flow and concentration distributions within urban canopy regions. Exceeding wind speeds and scalar concentrations are determined through cumulative probability densities. The non-uniform spatial distribution of scalar concentrations is found to be correlated with the velocity magnitude distribution. In particular, airflows with strong wind speeds near tall blocks contribute to a reduction in the scalar concentration in that region. The probability density functions of velocity magnitude for arrays with height variations become long-tailed as the horizontally averaged wind speeds increase. Accordingly, the probability density at high scalar concentrations is lower for arrays with height variations. Finally, the exceeding wind speeds and scalar concentrations for arrays with height variation can be expressed as linear functions of the mean wind speed.

Characteristics of electrohydrodynamic roll structures in laminar planar Couette flow

The behaviour of an incompressible dielectric liquid subjected to a laminar planar Couette flow with unipolar charge injection is investigated numerically in two dimensions. The computations show new morphological characteristics of roll structures that arise in this forced electro-convection problem. The charge and velocity magnitude distributions between the two parallel electrodes are discussed as a function of the top wall velocity and the EHD Rayleigh number, T for the case of strong charge injection. A wide enough parametric space is investigated such that the observed EHD roll structures progress through three regimes. These regimes are defined by the presence of a single or double-roll free convective structure as observed elsewhere (Vazquez et al 2008 J. Phys. D 41 175303), a sheared or stretched roll structure, and finally by a regime where the perpendicular velocity gradient is sufficient to prevent the generation of a roll. These three regimes have been delineated as a function of the wall to ionic drift velocity , and the T number. In the stretched regime, an increase in can reduce charge and momentum fluctuations whilst in parallel de-stratify charge in the region between the two electrodes. The stretched roll regime is also characterised by a substantial influence of on the steady development time, however in the traditional non-stretched roll structure regime, no influence of on the development time is noted.

Numerical analysis of flow in a highly efficient flotation column

AbstractFor the purpose of optimization by numerical analysis, a highly efficient flotation column named cyclonic‐static micro‐bubble flotation apparatus, which is widely used in mineral processing, was simulated with computational fluid dynamics to study the distributions of velocity magnitude, pathlines, turbulent intensity, and turbulent kinetic energy under different discretization schemes, turbulence models, and rotational speeds of pump. This simulation was based on the volume of fluid multiphase and multiple reference frame models. Spatial discretization scheme had an obvious effect on the velocity distribution in the column and revolving flotation sections, especially in the former. The introduction of a turbulence model changed the velocity distribution, the turbulence state, and the pathlines in the column and revolving flotation sections. Moreover, the standard, renormalization group (RNG), and realizable k‐epsilon turbulence models had numerous differences. Among these models, the RNG and realizable turbulence models had the most similar results. As the rotational speed of pump increased, velocity and turbulence field intensified. The flow field in the column flotation section differed from that in the revolving flotation section. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Study on Numerical Simulation Method of Aerodynamic Performance of High-Speed Train on Bridge

The dynamic mesh method that could simulate the actual moving of train was used to calculate the aerodynamic coefficients of train on bridge with wind barriers of various heights, and the static pressure distributions around the train body and velocity magnitude distributions were analyzed, the results computed by dynamic mesh method were compared with that computed by traditional static mesh method. The results show that the aerodynamic coefficients of train and flow field characteristics computed by the two methods agree well under the configuration without wind barriers. However, there is considerable difference between the results computed by the two methods with the installation of wind barriers. It is found that the dynamic mesh method is more reasonable to simulate the aerodynamic coefficients of train with wind barriers by analysis of the contour of static pressure distributions and velocity magnitude distributions. The wind barriers effectively decrease the positive pressure on windward train body and negative pressure on train roof, mainly reduce the side force coefficient, lift force coefficient, rolling moment coefficient. Therefore, the aerodynamic performance of train on bridge under crosswind is improved.