Flow Generation Research Articles

Numerical assessment of heat transfer and entropy generation of a mixed convection ferrofluid flow under the effect of a non-uniform magnetic field

Numerical assessment of heat transfer and entropy generation of a mixed convection ferrofluid flow under the effect of a non-uniform magnetic field

Numerical Analysis of Magnetohydrodynamics Mixed Convection and Entropy Generation in a Double Lid‐Driven Cavity Using Ternary Hybrid Nanofluids

AbstractThe present study numerically investigates the effects of a magnetic field on mixed convection flow and entropy generation within a double lid‐driven square cavity filled with a hybrid nanofluid. The flow is induced by two isothermally heated semi‐circles located on the bottom and left walls of the cavity. The cavity is filled with a ternary composition of hybrid nanofluid (aluminum oxide/silver/copper oxide‐water) and is exposed to a uniform magnetic field. The velocity ratio of the moving lids and the radius ratio of the semi‐circles are key parameters in the analysis. The study employs the finite volume method and full multigrid acceleration to solve the coupled continuity, momentum, energy, and entropy generation equations, along with the relevant boundary conditions. Key dimensionless parameters considered include the Hartmann number (0 ≤ Ha ≤ 100), Richardson number (0.01 ≤ Ri ≤ 1), hybrid nanofluid volume fraction (3% ≤ ϕ ≤ 12%), internal semi‐circle radius ratio (β = 0.5 and 1), and velocity ratio (−2 ≤ λ ≤ 2). Results revealed that the optimal heat transfer is achieved for Ri = 0.04, Ha = 100, ϕ = 0%, β = 1, and λ = 0.5 with 63% enhancement. Moreover, the maximum entropy generation rates are obtained for the same parameters with a rate of 47%, reflecting the complex balance of enhanced heat transfer and associated irreversibility's. Results reveal also that heat transfer and entropy generation are a decreasing function of Hartmann number implying a suppress of fluid motion due to the Lorentz force. This study provides a valuable resource and parametric analysis for researchers and engineers, aiding in the design and optimization of thermal management systems for various industrial applications, including heat exchangers, nuclear reactors, and energy systems.

A first principles study of convection cells to shear flow instability in 2D Yukawa liquids driven by Reynolds stress

The stability of kinetic-level convection cells (wherein the magnitude of macroscopic and microscopic velocities are of same order) is studied in a two-dimensional Yukawa liquid under the effect of microscopic velocity perturbations. Our numerical experiments demonstrate that for a given system aspect ratio viz., the ratio of system length to its height and number of convective rolls initiated , the fate of the convective cells is decided by . For , Reynolds stress is found to be self-consistently generated and sustained, which results in tilting of convection cells, eventually leading to shear flow generation, whereas for , parallel shear flow is found to be untenable. An unambiguous quantitative connection between Reynolds stress and the onset of shear flow using particle-level data is established without free parameters. The growth rate of the instability, the role of frictional forces, generalization of our findings and the possibility of realizing the same in experiments are also discussed.

Analysis of heat transfer in magnetized Williamson fluid over a porous curved oscillating surface: Entropy generation

This paper provides an innovative idea to perform the analysis of entropy generation in the time-dependent flow of Williamson liquid toward an oscillating curvy porous surface. The characteristics of the transport phenomenon are improved by taking thermal and mass relaxation parameters in the energy and concentration equations respectively by utilizing a modulated form of Fourier and Fick laws known as Cattaneo–Christov heat and mass flux models. The mathematical form of the entire flow model is simplified by incorporating a curvilinear coordinate system. The obtained set of partial differential equations is then solved by the homotopy analysis method (HAM) which transforms them into convergent series form. The effects of various pertinent flow parameters on dimensionless pressure, entropy generation, velocity, and temperature fields are shown graphically. Furthermore, the variations in Sherwood number, skin friction coefficient, and local Nusselt number are presented in tabular form. It is observed from this study that the temperature and entropy generation increase with the radius of curvature parameter.

Optimization of In-Motion EV Charging Infrastructure for Power Systems Using Generative Adversarial Network-Based Distributionally Robust Techniques

This paper presents an innovative optimization framework for the co-management of dynamic electric vehicle (EV) charging lanes and power distribution networks, addressing grid stability amidst fluctuating EV charging demands. Integrating generative adversarial networks (GANs) and distributionally robust optimization (DRO), the framework models uncertainties in traffic flow and renewable energy generation, optimizing system performance under worst-case conditions to mitigate risks of grid instability. Applied to a highway with eight dynamic charging lanes (500 kW per lane), serving up to 50 EVs simultaneously, the framework balances energy contributions from 15 renewable generators (60% of the mix) and 10 non-renewable generators. Simulation results highlight its effectiveness, maintaining grid stability with voltage deviations within 0.02 p.u., reducing energy losses to under 0.8 MW during peak traffic (1500 vehicles per hour), and achieving 95% lane utilization. Dynamic charging enabled EV users to save USD 0.08 per kilometer through reduced stationary charging downtime, optimized travel efficiency, and lower energy costs. Additionally, the system minimizes maintenance costs by optimizing lane and grid reliability. This study underscores the potential of GAN-based DRO methodologies to enhance the efficiency of power grids supporting dynamic EV charging, offering scalable solutions for diverse regions and traffic scenarios.

Solitary wave structure of transitional flow in the wake of a sphere

The soliton-like coherent structure (SCS), which has been verified to exist in both transitional and turbulent boundary layers [Y. S. Kachanov, “Physical mechanisms of laminar-boundary-layer transition,” Annu. Rev. Fluid Mech. 26, 411–482 (1994); C. Lee, “New features of CS solitons and the formation of vortices,” Phys. Lett. A 247, 397–402 (1998); C. Lee and J. Z. Wu, “Transition in wall-bounded flows,” Appl. Mech. Rev. 61, 030802 (2008); and C. Lee and X. Jiang, “Flow structures in transitional and turbulent boundary layers,” Phys. Fluids 31, 111301 (2019)], still poses a challenge in the understanding of its formation and behavior. In our previous study [Niu et al., “Turbulence generation in the transitional wake flow behind a sphere,” Phys. Fluids 36, 034127 (2024)], the SCS was also found to exist in the transitional wake flow behind a sphere. In the present study, the formation and evolution of the SCS is further investigated at various Reynolds numbers by numerical simulation. The results show that at the early stage of the turbulence transition, the SCS appears as a form of wave packet during the Tollmien–Schlichting (T–S) wave stage. With the increase in the Reynolds number, the SCS reaches its maximum amplitude downstream where the velocity discontinuity occurs. This position is located after the breakdown of the T–S wave and the three-dimensional structure is formed. Then, the SCS conserves its shape and amplitude over a long distance downstream. The relationships among the SCS, the spikes, the vortex structures, and the high-shear layers are further analyzed. It is found that the SCS in the wake flow has similarities to the phenomena observed in boundary layer flows during the turbulent transition. The vortex structures and high-shear layers mostly wrap around the border of the SCS. The vortex structure is considered to be a consequence of the development of the SCS rather than its cause.

Analytical approach to control the irreversibilities in a chemically reactive nanofluid flow over a Darcy–Forchheimer medium with nonuniform heat source/sink

AbstractIn real‐world processes, such as heat transfer, fluid flow, and chemical reactions, irreversibility occurs frequently, which induces an augment in entropy. The optimization of the entropy generation in a mechanical system is one of the fundamental areas of research to channel the energy of the system for utilization. This research exhibits an entropy generation in a nanofluid flow drenched in a fluid‐saturated non‐Darcy porous medium toward a stagnation point. The flow line also experiences the existence of nonuniform heat generation/absorption following the first‐order chemical reaction, which enhances the applicability of this model in different domains of science and engineering. A special form of the Lie group approach is applied to revert the governing partial differential system into its self‐similar ordinary differential form. The solutions of the transformed nonlinear ODEs are acquired analytically through the DTM ‐Padé as well as numerically by the Runge–Kutta–Fehlberg (RKF‐45) method coupled with the shooting process. The fallouts are vividly sketched graphically. One of the upshots reveals that the escalation of space and temperature‐reliant heat absorption parameters can optimize the thermal irreversibility of the system and so as the total entropy generation. Meanwhile, by incrementing the Darcy parameter from 0 to 0.8, the wall shear stress decays by 23.7%, whereas with the same hike in the Forchheimer resistance factor, declines the rate of heat and mass transfer approximately by 2.6% and 3.6%, respectively. Another upshot reveals that with the escalation of the space‐dependent heat source parameter from 0.1 to 0.5, the Nusselt number significantly decreased by 23.9%. Meanwhile boosting the temperature‐reliant heat sink parameter from ‐0.1 to ‐0.5 causes an inclination in the rate of heat transportation by 10.5%. Moreover, it is found that mass transport irreversibility can be controlled by enhancing the constructive chemical reaction rate. We hope that this study will be beneficial for many engineering and industrial processes, particularly in geothermal energy extraction, nuclear waste disposal management, groundwater filtration machinery and food processing equipment.

Entropy generation and heat convection analysis of second-grade viscoelastic nanofluid flow in a tilted lid-driven square enclosure: A finite difference approach

Entropy generation and heat convection analysis of second-grade viscoelastic nanofluid flow in a tilted lid-driven square enclosure: A finite difference approach

Spontaneous net flow generation using passive artificial cilia in the nucleate boiling region

The occurrence of spontaneous net flows in nature is fascinating. Here, we report spontaneous net flow generation using passive artificial cilia consisting of directional fabric in the nucleate boiling regime. Surprisingly, by placing simple ordinary flocking rayon fibers at an angle of approximately 18 degrees on a base cloth on the circular wall in a container as the artificial cilia, we observed the circular flow of the angular velocity of up to ∼2 rad/s (the average velocity of up to ∼34 mm/s) in the nucleate boiling regime. Moreover, by the observation of a high-speed camera (960 fps), we found that the bubbles rise obliquely at a high velocity of about 80–180 mm/s, which drives the net flow. Our findings should contribute to a better understanding of spontaneous flows in nature and should be applied to utilize unused heat, such as factory waste heat effectively.

An explicit peridynamics model for hydraulic fracturing in porous media

PurposeThe purpose of this paper is to systematically investigate the hydraulic fracture branching phenomena in porous media under different loading conditions and the stepwise phenomenon. The effect of the pore pressure in hydraulic fracturing branching is studied, and more evidence for the stepwise phenomenon with the peridynamics approach is provided.Design/methodology/approachA fully coupled fluid-filled explicit peridynamics model is developed to simulate the complex evolution of crack branching and stepwise phenomena in saturated porous media. Based on the peridynamics theory, an explicit time integration scheme is used to solve the coupled equation system including rock deformation, fluid flow and fracture propagation. Using the proposed model, a series of peridynamic computational tests are performed to examine two common kinds of phenomena observed in hydraulic fracturing: the crack branching phenomenon and the stepwise phenomenon.FindingsFor crack branching phenomenon, the results obtained indicate that sufficient loading is required in order to initiate the crack branching process. Compared with the stress applied on crack surfaces condition, crack branching is more easily induced with the stress applied on boundaries. In addition, for the fluid-driven crack (stress applied on crack surfaces), the existence of pore pressure will depress the growth and branching of the crack. For stepwise phenomena, the results obtained indicate that the peridynamics is a promising tool to study the stepwise phenomenon. The stepwise phenomenon is more distinct under mechanical loading conditions due to the solid behaviour. A sudden jump or crack extension will happen when enough energy is accumulated in the hydraulic fracturing system.Research limitations/implicationsIn this study, the explicit method is used, which means it is conditionally stable, and the critical time step needs to be decided. The reason to use the explicit method is for the study purpose; the explicit method is faster and has no need for matrix inversions.Originality/valueThis study helps to understand the effect of the pore pressure in hydraulic fracturing branching and provides more evidence for the stepwise phenomenon with peridynamics.

Application of fluid dynamics in modeling the spatial spread of infectious diseases with low mortality rate: A study using MUSCL scheme

Abstract This study presents a comprehensive mathematical framework that applies fluid dynamics to model the spatial spread of infectious diseases with low mortality rates. By treating susceptible, infected, and treated population densities as fluids governed by a system of partial differential equations, the study simulates the epidemic’s spatial dynamics. The Monotone Upwind Scheme for Conservation Laws is employed to enhance the accuracy of numerical solutions, providing a high-resolution approach for capturing disease transmission patterns. The model’s analogy between fluid flow and epidemic propagation reveals critical insights into how diseases disperse geographically, influenced by factors like human mobility and environmental conditions. Numerical simulations show that the model can predict the evolution of infection and treatment population densities over time, offering practical applications for public health strategies. Sensitivity analysis of the reproduction number highlights the influence of key epidemiological parameters, guiding the development of more efficient disease control measures. This work contributes a novel perspective to spatial epidemiology by integrating principles of fluid dynamics, aiding in the design of targeted interventions for controlling disease outbreaks.

Numerical simulation of various flow regimes in water delivery systems

Transient flow frequently occurs in water delivery systems, including various flow regimes such as water hammer, free surface flow, and slug flow. Current models often oversimplify these phenomena by simulating single-phase flow or using simplistic one-dimensional assumptions for the gas-water interface, neglecting interface instability. Although two-fluid models can address some of these issues, they cannot simulate open channel flow and have not yet been applied to transient flow scenarios. To date, no single model has been able to simultaneously simulate all these flow regimes while overcoming these limitations. To address this gap, the two-fluid model is enhanced in this paper. For water hammer simulation, a gas volume fraction of zero is assumed, and a TVB unsteady friction model is introduced to enhance numerical accuracy. For open channel flow, a variable wave speed equation and a new state equation are presented. Despite the different state equations required for various flow regimes, a Roe-type scheme is introduced to solve the two-fluid model. This approach accurately simulates water hammer, free surface flow (including open channel flow and stratified flow), and slug flow. An experimental pipeline system is designed to validate the proposed model's ability to simulate water hammer. Additionally, several cases are used to verify the model's capability in simulating open channel flow, stratified flow, and slug flow. The model accurately predicts the occurrence of slug flow, consistent with experimental flow pattern maps, and effectively simulates the evolution of slug flow, closely matching the measured gas-water interface. The effects of gas volume fraction, pipe length, and pipe slope on slug flow are systematically discussed. Results indicate that smaller initial gas volume fractions, longer pipe lengths, and upward pipe slopes increase the likelihood of slug flow generation within the pipeline, which should be minimized during design. Abbreviations: TVB: Trikha-Vardy-Brown model; Cr: Courant number

Density-dependent flow generation in active cytoskeletal fluids

The actomyosin cytoskeleton, a protein assembly comprising actin fibers and the myosin molecular motor, drives various cellular dynamics through contractile force generation at high densities. However, the relationship between the density dependence of the actomyosin cytoskeleton and force-controlled ordered structure remains poorly understood. In this study, we measured contraction-driven flow generation by varying the concentration of cell extracts containing the actomyosin cytoskeleton and associated nucleation factors. We observed continuous actin flow toward the center at a critical actomyosin density in cell-sized droplets. The actin flow exhibited an emergent oscillation in which the tracer advection in the bulk solution periodically changed in a stop-and-go fashion. In the vicinity of the actomyosin density where oscillatory dynamics occur, the velocity of tracer particle motion decreases with actomyosin density but exhibits superdiffusive motion. Furthermore, the increase or decrease in myosin activity causes the oscillatory flow generation to become irregular, indicating that the density-dependent flow generation of actomyosin is driven by an interplay between actin density and myosin force generation.

Magnetoacoustic wave propagation in the solar corona and filament dynamics

The formation of a S-shaped filament was investigated to determine if and how magnetoacoustic waves in the solar corona can trigger filament excitation. The study investigated how magnetoacoustic waves interact with two magnetic null points in the solar corona. Since the solar corona has a complex magnetic field structure, it is expected that magnetic structures are predominantly responsible for the occurrence of coronal events. Simulation methods are required because of the complex nature of the reconnection problem and the way MHD waves behave. Because of notable progress in the production of supercomputers and the enhancement of techniques, it is now possible to analyze the behaviour of nonlinear plasma near the magnetic null point through numerical methods. This article aims to explore the idea of a 2.5D null point pair and investigate the motion and generation of plasma flow resulting from a solitary magnetoacoustic pulse passing through a particular magnetic structure that contains two null points. In this statement, the PLUTO code, which is a type of code called Godunov, is used to solve a set of equations known as resistive magnetohydrodynamic equations. It was depicted that when transitioning from X-point to O-point, twisted formations are formed, which play a significant role in developing S-shaped filaments. These formations also have a vital function right before the excitement of the filaments.

Reflectionless internal wave propagation in an exchange flow of shallow two-layer medium in a channel with variable cross-section

The propagation of long linear internal waves of arbitrary shape in a steady flow of shallow two-layer fluid in a narrow channel of variable cross-section is considered. The flow velocities in the layers are oppositely directed. It is shown that there are three classes of flows in which waves can propagate without reflection in both directions, and the properties of such flows are examined. A detailed analysis has demonstrated that only one of these classes contains regular flows of unlimited extent, while the flows belonging to the other two classes are always limited (on one or both sides) by a singularity. Possible applications of the results obtained and prospects for further research are discussed.

Generation of shear flows induced by AE / EPM in LHD plasma

Abstract The generation of shear flows (SFs) by Alfven Eigenmodes (AEs) and energetic particle modes (EPMs) have important effects on the operation of future nuclear fusion reactors, because SFs regulate the saturation of the AEs/EPMs, the transport of EPs and thermal plasma, as well as the formation of transport barriers among other consequences. The aim of this study is the analysis of SFs generation during the saturation phase of AEs and EPMs in LHD plasma. Experiments performed in the 23rd and 24th LHD experimental campaigns are dedicated to explore the destabilization of AEs/EPMs in discharges with different heating patterns, thermal plasma and magnetic field configurations. In particular, the shots 176490 and 179697 show the destabilization of MHD bursts and energetic-ion-driven resistive interchange modes (EIC), respectively. Charge exchange spectroscopy measurements in both discharges indicate that the generation of SFs by AE/EPM is uncorrelated with the perturbation induced by the neutral beam injector (NBI). Nonlinear simulations performed using the gyro-fluid code FAR3d show the generation of zonal structures, especially SFs, induced during the saturation phase of Toroidal Alfven Eigenmodes (TAEs) triggered in the MHD burst as well as by the 1 / 1 EIC in the bursting phase. The simulations indicate that SFs are caused by the radial electric fields powered by energy transfers from the unstable AE/EPM towards the thermal plasma. The strongest SFs are measured during the EIC bursting phase once the 1 / 1 EPM overlaps with nearby resonances at the plasma periphery. Likewise, the largest SFs during the MHD burst are observed once TAEs radially overlap in the inner-middle plasma region.

Shear forces heat generation in MHD uniform flow of nanoliquid across a stretchable surface through Darcy medium

AbstractThe production of high‐quality polymers greatly relies on the flow mechanism of liquid with thermal characteristics. Thus, the prediction of specific flow and thermal transport rate is important here. So, a uniform flow of viscous nanofluid over a bilateral, linearly stretching, flat, heated surface with the effect of medium porosity and magnetic field is studied in this theoretical investigation. A two‐phase model for the nanofluid is employed to improve the thermal characteristics of fluid flow with heat generation via shear forces in the system. The proposed physical model is analyzed through the similarity analysis and numerical computations with various physical parameters such as the velocity ratio parameter, magnetic number, and so forth. The built‐in function of the MATLAB bvp5c is used to find the numerical solution of the governing set of equations. All the findings of the simulation for the fluid flow under thermal and mass concentration influence are justified with reliable physical reasoning. Variation in the flow field is observed for both the magnetic and porosity parameters between the surface stretching and free stream velocity as well as for different values of velocity ratio parameters. Moreover, heat transport rate and fluid friction at surface to fluid are also calculated in view of numeric data given in tabulated form.

Guidelines for preparation and flow cytometry analysis of human nonlymphoid tissue DC.

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs, and various nonlymphoid tissues. Within this article, detailed protocols are presented that allow for the generation of single-cell suspensions from human nonlymphoid tissues including lung, skin, gingiva, intestine as well as from tumors and tumor-draining lymph nodes with a subsequent analysis of dendritic cells by flow cytometry. Further, prepared single-cell suspensions can be subjected to other applications including cellular enrichment procedures, RNA sequencing, functional assays, etc. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists.

Analyzing thermal performance and entropy generation in time-dependent buoyancy flow of water-based over rotating sphere with ternary nanoparticle shape factor

Abstract The heat transfer augmentation, solar power systems, medical equipment, semiconductor cooling, aerospace, and automotive industries all use ternary hybrid nanofluids (Thnf). The current study is mainly about a magnetized Thnf flow that can't be squished around a spinning sphere that has different viscosity, thermal conductivity, and shape (brick, platelets, cylinder, blade). The heat transport simulation incorporates the principles of viscous dissipation and joule heating. Water is mixed with silver, magnesium oxide, and iron trioxide to make the ternary hybrid nanofluid. Similarity substitution converts model equations to ordinary differential equations (ODEs). Runge-Kutta fourth order numerically estimates the non-dimensional set of ODEs. For certain emergent parameters, velocity, temperature, entropy generation, Nusselt number, and skin friction are computed and analyzed. The research shows that entropy generation increases with brinkman number, nanoparticle volume fraction and magnetic parameters and reduces with temperature difference parameter. Increasing the unsteadiness parameter upsurges velocity in the x-direction, but decreases it in the z-direction and temperature curve. Skin friction upsurges in the x-direction and declines in the z-direction with rotation. Platelet-shaped nanoparticles usually outperform blade, brick, and cylinder shapes. When mass suction $( S )$ is elevated from 1.0 to 2.0, the heat transfer rate increases by 47.25% for the Brick form, 47.26% for the Platelets shape, 35.08% for the Cylinders shape, and 37.65% for the Blades shape. Comparing the results to prior literature shows excellent agreement.

Smooth Muscle Mechanosensitivity Generates and Maintains Pressure Gradients Across the Intestine.

The gut, the ureter, or the Fallopian tube all transport biological fluids by generating trains of propagating smooth muscle constrictions collectively known as peristalsis. These tubes connect body compartments at different pressures. We extend here Poiseuille's experiments on liquid flow in inert tubes to an active, mechanosensitive tube: the intestine. We use as a miniature myogenic peristaltic pump model, the fetal chicken gut, and measured the flow and contractile wave propagation as a function of the initially applied pressures and pressure gradients. We dissect the molecular pathways of smooth muscle mechanosensitivity by measuring the force generated by gut rings in different pharmacological conditions. We demonstrate that smooth muscle contractions in response to stretch or pressure is mediated by L-type Ca2+ channels and IP3 receptors. We show that this positive-feedback mechanosensitive behavior can spontaneously generate pressure gradients across gut segments initially subject to equal pressure; this same mechanism tends to stabilize initially applied pressure gradients; it can act jointly or compete with the pressure gradient induced by directional peristaltic waves. We demonstrate that high pressure differentials can reverse the physiological propagation direction of contractile waves imparted by interstitial cell of Cajal pacemaker activity. We find that flow rate increases with tube length, but that the maximum pressure differential generated depends solely on smooth muscle contractile force and on the initial resting pressure applied inside the organ. We provide fundamental mechanical and hydrodynamic insight into the myogenic mechanisms of transport in the gastrointestinal tract. We scale up our results to other human peristaltic organs and discuss their implications for pathophysiology of intestinal obstruction, vesicoureteral reflux and endometriosis.