Fluid Motion Research Articles

Enhancing Microfluidic Chip Functionality via Thermal Gradient‐Driven Optofluidic Manipulation

AbstractThermal gradient‐driven fluid motion, also known as thermal convection, is a common and significant phenomenon in nature. The utilization of localized thermal gradients to induce convection has emerged as a competitive approach in microfluidic chips. This technique enables the long‐distance transportation of substances under the influence of low‐power lasers. In this paper, an innovative optofluidic micro‐platform is presented that possesses a simple structure, easy operation, and excellent expandability. A UV nanosecond laser is utilized to create a high photothermal conversion region (HPCR) within the carbon nanotube‐doped PDMS substrate. Subsequently, the HPCR is subjected to irradiation for generating localized thermal gradients in the microfluidic chip. This resulted in Rayleigh–Bernard convection formation and facilitated long‐range transport and control of fluids and particles. Under low‐power laser irradiation, particles can be transported at speeds up to 0.18 mm s−1. In addition, the optofluidic platform shows significant potential for a range of functionalities, including fluid mixing and material sorting. The methodology described here allows for the rapid integration of new functionalities into existing chips while maintaining cost effectiveness and efficiency. This technique holds great promise for expanding the use of microfluidic devices in diverse fields, including chemistry, health sciences, materials science, and biomedicine.

Analysis of thermal conductivity variation in magneto-hybrid nanofluids flow through porous medium with variable viscosity and slip boundary

Hybrid nanoparticles, which are nanoparticles composed of multiple materials or phases, find applications in various fields due to their unique properties resulting from the combination of different materials. In such fluids, viscosity changes significantly in response to alterations in temperature or pressure. For example, these fluids become less viscous as they are heated and more viscous as they are cooled. Similarly, in certain situations, the application of a temperature variation can cause a change in viscosity. This property is commonly observed in materials like polymers and some oils. The article aims to investigate the heat transfer and flow behavior of fluid from an elastic sheet of hybrid nanoparticles, considering the temperature-dependent variable viscosity and thermal conductivity. The obtained equations for the mathematical model are partial differential equations converted to ODEs by applying a suitable similarity transformation. The findings show that the magnetic field opposes fluid motion. Our main findings are that adding nanoparticles to the base fluid significantly increased its heat conductivity. This improvement has great potential for uses requiring effective heat transmission, especially in engineering systems where heat dissipation plays a crucial role. The study also reveals the complex relationships that influence thermal conductivity, including slip boundary effects, viscosity fluctuations, magnetohydrodynamic effects, and porous media dynamics. Understanding these interactions is critical for optimizing heat transport processes in porous media applications. Comprehending these interplays is essential for refining heat transport mechanisms in applications involving porous media. The graphical representations are used to explain the physical behavior of various model parameters. Previous outcomes are also contrasted with the current ones. The findings show that the magnetic field opposes fluid motion.We range the subsequent list of values for parameters in every graph unless indicated accordingly.ϵ=0.1,Pr=2,M=0.5,R=0.2,K=5,fw=0.1,s=0.1 ,λ=1,φ1=0.02,φ2=0.04.

Observation of blood motion in the internal jugular vein by contact and contactless photoplethysmography during physiological testing: case studies.

Central venous pressure is an estimate of right atrial pressure and is often used to assess hemodynamic status. However, since it is measured invasively, non-invasive alternatives would be of great utility. The aim of this preliminary study was a) to investigate whether photoplethysmography (PPG) can be used to characterize venous system fluid motion and b) to find the model for venous blood volume modulations. For this purpose, we monitored the internal jugular veins using contact (cPPG) and video PPG during clinically validated physiological tests: abdominojugular test (AJT) and breath holding (BH). Video PPG and cPPG signals were captured simultaneously on the left and right sides of the neck, respectively. ECG was also captured using the same clinical monitor as cPPG. Two volunteers underwent AJT and BH with head up/down, each with: baseline (15s), experiment (15s), and recovery (15s). Video PPG was split into remote PPG (rPPG) and micromotion detection. All signal modalities were significantly affected by physiological testing. Moreover, cPPG and micromotion waveforms exhibited primary features of jugular vein waveforms and, therefore, have great potential for venous blood flow monitoring. Specifically, remote patient monitoring applications may be enabled by this methodology, facilitating physical collection without a specially trained care provider.

Effects of Darcy and Viscous Dissipation on Natural Convection Flow in a Vertical Tube Partially Filled with Porous Material under Convective Boundary Condition

In this paper, a study is presented considering the effects of Darcy and Viscous dissipation in a steady natural convection incompressible fluid through a vertical composite tube partially filled with a porous material. The fluid motion in the vertical composite tube is caused by a temperature gradient due to heat applied to the wall of the tube. The Brinkman Darcy extended model was used to stimulate the fluid flow under the working fluids of water and air. The Homotopy pertubation method was used to solve the temperature and velocity equations in both the clear and porous fluids. An increase in the Brinkman number increases the temperature and velocity profiles of both working fluids. An increase in the thickness of the porous material can be used to increase the velocity of the fluid in the composite vertical tube. An increase in the internal conductive resistance leads to a decrease in the buoyancy force and, as a result, the fluid thickness, which leads to a decrease in the velocity of the fluid.

Viscoelastic fluid flow on channel in porous medium with Soret and Dufour along with the effect of activation energy and suction and blowing

This study conducts a thorough numerical analysis of a complex problem involving magnetohydrodynamic flow, radiation, activation energy, Soret, the Dufour effect, and heat transfer in a permeable channel for a Maxwell fluid. Governing equations for momentum, concentration, and heat are transformed into ordinary differential equations through a similarity transformation, enabling focused analysis. Utilizing a fourth-order Runge-Kutta scheme, we compute dimensionless velocity, temperature, and concentration fields for the steady motion of a Maxwell fluid in a channel. To ensure accuracy, our results are validated against existing research, showing excellent agreement. The study investigates the impact of various physical parameters on fluid motion, revealing insights such as decreased velocity and concentration with increased chemical reaction, and rising fluid temperature. Additionally, concentration distribution decreases with a chemical reaction and a higher Schmidt number. This research enhances understanding of complex fluid dynamics, providing valuable insights for engineering applications, particularly in industries requiring precise fluid behavior control.

Numerical analysis of thermal improvement in hydrogen‐based host fluids under buoyancy force and EPNM effects: Study for vertical cylinder

AbstractThe nanofluids became much of interest due to their superior heat mechanism over the conventional fluids. The addition of nanoparticles in the host solvent enhances the internal ability of the liquid to store and transmit heat. Therefore, these fluids are widely used in biomedical engineering, detergents, medication, applied thermal engineering, mechanical, and chemical engineering and so forth. Keeping in mind the significance of nanofluids, this study is conducted to investigate the comparative heat transmission in and under the Effective Prandtl Number Model (EPNM) effects over a vertical permeable cylinder. Formulation of the model is carried out over a vertical cylinder about the stagnation point and the heat transport model is achieved after the successful implementation of the cylindrical stream function, nanofluids effective characteristics, and cylindrical similarity equations. The mathematical treatment was done via RK technique and furnished the results. The nanofluids have the capacity to control the fluid motion more effectively than ordinary fluid and combined convection is better where rapid fluid movement is desired. In the existence of EPNM, higher heat transmission is achieved and is prominent for based on their thermophysical values. Further, the skin friction and Nusselt number are optimum for against .

Remote control of fluid motion in a channel by acoustic holography

A new method for manipulating fluid movement using sound waves is presented in this paper. The method relies on acoustic streaming near the free surface of the fluid in a channel with an open top. The sound waves are modulated in phase using acoustic phase holography, which creates a periodic phase pattern from 0 to 2π along a straight path on a target plane. The paper also describes an experimental design to study the main factors influencing the method, such as frequency, number of phase patterns in the path, and sound pressure amplitude. The paper shows that phase pitch and voltage significantly affects fluid speed and that there is a good match between the theoretical and experimental results. Furthermore, the article reports additional experiments with different channel shapes to demonstrate the versatility of the method in controlling fluid motion. The highest fluid speed observed was 0.4 mm/s at a frequency of 1300 kHz and a phase pitch of 5. The paper also investigates the effect of changing the frequency on reversing the flow direction in a U-shaped channel, both experimentally and theoretically. The paper concludes that this method could be a suitable alternative to other acoustic devices for inducing fluid motion because of its simple and flexible design, fabrication, accuracy, and ability to handle complex channels.

Multivariate Peristalsis in a Straight Rectangular Duct for Carreau Fluids

Peristaltic flow in a straight rectangular duct is examined imposed by contraction pulses implemented by pairs of horizontal cylindrical segments with their axes perpendicular to the flow direction. The wave propagation speed is considered in such a range that triggers a laminar fluid motion. The setting is analyzed over a set of variables which includes the propagation speed, the relative occlusion, the modality of the squeezing pulse profile and the Carreau power index. The numerical solution of the equations of motion on Cartesian meshes is grounded in the immersed boundary method. An increase in the peristaltic pulse modality leads to the reduction in the shear rate levels on the central tube axis and to the movement of the peristaltic characteristics to higher pressure values. The effect of the no slip side walls (NSSWs) is elucidated by the collation with relevant results for the flow field produced under the same assumptions though with slip side walls (SSWs). Shear thinning behavior exhibits a significantly larger effect on transport efficiency for the NSSWs duct than on the SSWs duct.

Dynamics of Fluids in the Cavity of a Rotating Body: A Review of Analytical Solutions

Since the middle of the 20th century, an understanding of the diversity of the natural magnetohydrodynamic phenomena surrounding us has begun to emerge. Magnetohydrodynamic nature manifests itself in such seemingly heterogeneous processes as the flow of water in the world’s oceans, the movements of Earth’s liquid core, the dynamics of the solar magnetosphere and galactic electromagnetic fields. Their close relationship and multifaceted influence on human life are becoming more and more clearly revealed. The study of these phenomena requires the development of theory both fundamental and analytical, unifying a wide range of phenomena, and specialized areas that describe specific processes. The theory of translational fluid motion is well developed, but for most natural phenomena, this condition leads to a rather limited model. The fluid motion in the cavity of a rotating body such that the Coriolis forces are significant has been studied much less. A distinctive feature of the problems under consideration is their significant nonlinearity, (i.e., the absence of a linear approximation that allows one to obtain nontrivial useful results). From this point of view, the studies presented here were selected. This review presents studies on the movements of ideal and viscous fluids without taking into account electromagnetic phenomena (non-conducting, non-magnetic fluid) and while taking them into account (conducting fluid). Much attention is payed to the macroscopic movements of sea water (conducting liquid) located in Earth’s magnetic field, which spawns electric currents and, as a result, an induced magnetic field. Exploring the processes of generating magnetic fields in the moving turbulent flows of conducting fluid in the frame of dynamic systems with distributed parameters allows better understanding of the origin of cosmic magnetic fields (those of planets, stars, and galaxies). Various approaches are presented for rotational and librational movements. In particular, an analytical solution of three-dimensional unsteady magnetohydrodynamic equations for problems in a plane-parallel configuration is presented.

Implosion mechanisms of underwater ring-stiffened metallic cylindrical shells

Underwater cylindrical shells are prone to implosion due to the surrounding high hydrostatic pressure, and introducing ring-rib is a promising approach to reduce the risk. However, the influences of the ring-rib on the deformation mode and the fluid-structure interaction mechanism are still unclear. This paper investigates the dynamic response of ring-stiffened cylindrical shells during the implosion process. The finite element model is firstly established and the numerical simulation is verified by the existing experiment. Then, the numerical method is used to simulate the implosion of ring-stiffened cylindrical shells with various geometrical parameters. The fluid motion, induced pressure and deformation features are investigated and the relationship between them is clarified. Finally, pure and ring-stiffened cylindrical shell implosions are compared and parametric analyses are performed by varying the number and thickness of ring-ribs. Results show that ring-stiffened cylindrical shells with higher collapse resistance deform asymmetrically and the flow field response changes depending on the deformation mode. Introduction of ring-ribs can significantly increase the critical pressure and reduce the percentage of induced pressure. As the number and thickness of ribs increased, the critical and peak implosion pressures of the ring-stiffened cylindrical shells increased by 153% and 146%, respectively.

Numerical simulation analysis of stable flow of hydrate slurry in gas-liquid-solid multiphase flow

The study of multiphase flow characteristics of hydrate slurry was crucial for controlling the risks associated with hydrate slurry transport in deep-water oil and gas operations. Currently, multiphase flow research on the hydrate slurry flow system focuses on two-phase (solid-liquid) flow studies in single short straight pipes or elbows. This paper established a geometric model based on an experimental loop of high-pressure natural gas hydrate slurry. The Euler model contained n momentum equations and continuity equations for each term, and the Euler model can couple the pressure term with the surface exchange coefficients. Therefore, Euler model was suitable to deal with complex fluid motion problems. Such as bubble flow problem, floating problem, particle suspension problem and fluidized bed problem. In this paper, the hydrate particles in the grout were set as regular round spheres and do not decompose, so the Euler model was suitable for the simulation of the gas-liquid-solid three-phase flow of hydrate grout in the loop. The Euler model was used to simulate the three-phase (gas-liquid-solid) expansion in the loop, focusing on the influence of hydrate slurry inlet flow rate, inlet hydrate volume fraction, liquid phase viscosity and pipe diameter on slurry flow characteristics. The results are as follows:1) Based on orthogonal experiments, pipe diameter has the most significant impact on the pressure drop of the entire pipe section, while liquid phase viscosity has the greatest impact on the average aggregation particle diameter of hydrate on the cross section.2) The distribution of hydrate phase is related to the direction of the loop. Under the influence of gravity, hydrates are primarily dispersed in the liquid phase, with a high concentration in the solid-liquid mixing zone, tend towards the gas phase zone. Hydrate particles are symmetrically distributed in the vertical cross-section, with smaller particle diameters in the solid-liquid mixing zone compared to the gas phase and liquid phase zone 3). In the elbow section, centrifugal force and density difference cause hydrate particles to aggregate towards the lower pipe wall on the outside of the elbow. This results in the disappearance of the liquid phase zone, higher hydrate concentration on the outside of the elbow, and smaller hydrate particle diameter in the solid-liquid mixing zone compared to the gas phase zone.4). Throughout entire loop, the viscosity of the slurry in the solid-liquid mixing zone was the highest, and the volume fraction of hydrate particles was symmetrical both vertically and horizontally. To validate the simulation results, high-pressure multiphase flow hydrate generation experiments were conducted in a 6 MPa hydrate slurry experimental loop. The stable flow pressure drop value of the slurry was compared to the simulation results. The relative error between the simulated and experimental pressure drops is less than 15%, falling within an acceptable range and matching the experimental results. This proved that the multiphase simulation technique of hydrate slurry gas-liquid-solid in the loop can effectively guide the safe transportation of hydrate slurry under actual working conditions.

Fluid-reduced-solid interaction (FrSI): Physics- and projection-based model reduction for cardiovascular applications

Fluid-solid interaction (FSI) phenomena play an important role in many biomedical engineering applications. While FSI techniques and models have enabled detailed computational simulations of flow and tissue motion, the application of FSI can present challenges, particularly when data for constraining models is sparse and/or when fast computational simulations are required for assessment. In this paper, we propose a novel method for flexible-wall fluid dynamics in an ALE framework applicable for cardiovascular applications where adaptive fluid motion that emulates patient data is required. Efficiency and model simplicity are gained by a physics-based reduction to solid membrane formulations at the fluid-tissue interface combined with a Galerkin projection to a subspace spanned by boundary motion modes, leveraging snapshots observed from imaging data by use of Proper Orthogonal Decomposition (POD). The resulting fluid-reduced-solid interaction (FrSI) model is verified for a series of examples, illustrating efficacy and efficiency. Focusing on an idealized left ventricle model, we demonstrate homogenization of transmural active stress along with the capacity to accommodate prestress in the FrSI model, accounting for whole cycle mechanics by coupling to 0D pre- and afterload models (showing end-diastolic and end-systolic projected endocardial surface position errors of less than 1.5% and 3.5%, respectively). Further, we present strategies to compensate for the inherent approximation errors of the FrSI model, allowing for minimizing both the integral and spatial error between reduced and full-order model by re-calibrating parameters that govern diastolic and systolic function. Finally, the ability of FrSI to extrapolate to impaired system states (increased afterload, localized region of infarct) is shown, providing a simple yet effective strategy to enhance the POD subspace to further reduce errors. These results illustrate the potential of FrSI to streamline the simulation of hemodynamics in the heart and cardiovascular system.

Random processes in modeling durability of building and structure

The problem of buildings and structures durability during their long-term operation in aggressive environments is discussed. It is closely connected with the problem of destruction of composite materials as a random process of birth, development, and death of defects at chemical corrosion. The content of the study is to analyze the influence of non-stationary chemical reactions occurring in real conditions on these processes. The analysis is carried out taking into account the incidental physical phenomena affecting corrosion, the most important of which is the diffusion of initial substances and reaction products occurring under different hydrodynamic conditions, i.e., the nature of fluid motion and its pressure which stimulates corrosion. The synthesis of three processes – chemical kinetics, diffusion, and hydrodynamics – allows us to study one of the possible scenarios of corrosion process development as a Markov process based on the statistical theory of the “weakest” link and the joint distribution of the random material and geometric parameters. Numerical analysis of changes in elastic and electrical properties of composite materials under these conditions allows us to substantiate the technology of non-destructive control of changes in the state of the structure. The research results are based on mathematical and statistical modeling.

Advanced numerical simulation techniques in MHD fluid flow analysis using distributed fractional order derivatives and Cattaneo heat flux model

AbstractThis study investigates the flow and heat transfer characteristics of a second‐grade fluid over a flat surface with variable heat flux. Utilizing a mathematical model based on distributed order fractional derivatives, we offer a more precise representation of non‐Newtonian fluid behavior. The associated highly nonlinear equations are tackled numerically through an innovative amalgamation of the finite difference scheme and the technique. Our investigation thoroughly evaluates the influence of several critical parameters on the fluid's motion and thermal characteristics. Notably, the magnetic parameter significantly inhibits the fluid's velocity, illustrating the impact of magnetic forces. Additionally, the power law parameter leads to a decrease in both velocity and temperature profiles, highlighting its influence on fluid dynamics. Furthermore, changes in the Reynold number and the second‐grade fluid parameter are observed to cause a substantial increase in skin friction, by approximately 40% to 50%. These simulation results provide valuable insights into the complex interaction between fluid flow and heat transfer characteristics, enhancing our understanding of such systems in industrial applications.

NUMERICAL ANALYSIS IN ARTERIAL STENOSIS AFFECTED BY ISCHEMIC HEART DISEASE USING FINITE VOLUME METHOD

Atherosclerosis is the narrowing of blood vessels caused by the buildup of cholesterol plaque on the walls of the arteries. Excessive buildup of cholesterol plaque disrupts the circulatory system, thereby affecting the speed and pressure of blood flow. In the long term, atherosclerosis can cause ischemic heart disease. This study aims to analyze the influence of stenosis, initial velocity, and diameter on the velocity and pressure of blood flow in narrowed arteries that cause ischemic heart disease. In this research, a Navier Stoke mathematical equation model was built which was solved using the finite volume method with SIMPLE discretization (Semi Implicit Method for Pressure Linked Equations). Finite volume methods are used to analyze unstructured objects such as blood flow. SIMPLE discretization is implemented simply in two and three dimensions with a system of equations containing fluid motion. Matlab and Fluent are software used for process simulations, Matlab for visualizing graphs of numerical calculation results, and Fluent for visualizing blood flow. Based on the simulation results, it can be concluded that the smaller the diameter, the greater the stenosis, and the greater the initial velocity, the greater the blood flow velocity. On the contrary, the diameter gets smaller, the stenosis gets bigger, and the initial velocity gets bigger so that the pressure on the blood flow gets smaller. Blood flow simulation has the potential to contain ischemic heart disease if the maximum speed produced is greater than the maximum normal blood speed, namely 0.45 m/s.

Wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder

In this paper, we study wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder composed of a closely spaced array of thin vertical barriers, between which fluid can flow. A theoretical model is developed under full depth-dependent linearised water wave theory, where an effective medium equation and effective boundary conditions are employed, respectively, to describe the fluid motion inside the cylinder and match the flow between the fluid regions in and outside the metamaterial cylinder. A damping mechanism is introduced at the surface of the fluid occupied by the metamaterial cylinder to consider the wave power dissipation in narrow gaps between the thin vertical plates. The wave excitation forces acting on the cylinder and the hydrodynamic coefficients can be calculated straightforwardly in terms of the velocity potential inside the cylinder. An alternative way is by using the velocity potential outside the cylinder, the expression of which has the reduction of the integral and an infinite accumulation that are included in the straightforward expression. The results highlight the patterns of the radiated waves induced by the oscillation of the cylinder and the characteristics of the hydrodynamic coefficients. The metamaterial cylinder when fixed in place and with a damping mechanism included is found to capture more wave power than that of a traditional axisymmetric heaving wave energy converter over a wide range of wave frequencies.

Parametric Roll Motion Reduction of a Ship with a Passive Anti-Roll Tank

In this study, the influence of a U-tube passive anti-roll tank on parametric roll motion has been investigated as a mechanical absorber of a dynamic system. Specifically, this paper concentrates on how the initial conditions of a coupled roll motion and fluid motion in the tank act on the performance of an anti-roll tank. Parametrically excited roll motion was modeled as a single degree of freedom system incorporating heave and pitch effects by means of a time-varying restoring moment. Fluid motion in the tank was modeled as a single degree of freedom system. Coupled equations of motion were solved numerically and the results were presented in the time domain. Furthermore, the results were comparatively depicted as maximum roll amplitudes vs. initial values for a ship with and without an anti-roll U-tube tank.

Spontaneous Stochasticity Amplifies Even Thermal Noise to the Largest Scales of Turbulence in a Few Eddy Turnover Times.

How predictable are turbulent flows? Here, we use theoretical estimates and shell model simulations to argue that Eulerian spontaneous stochasticity, a manifestation of the nonuniqueness of the solutions to the Euler equation that is conjectured to occur in Navier-Stokes turbulence at high Reynolds numbers, leads to universal statistics at finite times, not just at infinite time as for standard chaos. These universal statistics are predictable, even though individual flow realizations are not. Any small-scale noise vanishing slowly enough with increasing Reynolds number can trigger spontaneous stochasticity, and here we show that thermal noise alone, in the absence of any larger disturbances, would suffice. If confirmed for Navier-Stokes turbulence, our findings would imply that intrinsic stochasticity of turbulent fluid motions at all scales can be triggered even by unavoidable molecular noise, with implications for modeling in engineering, climate, astrophysics, and cosmology.

The wave resonances and time-dependent wave motion in stratified fluid with permeable bottom

The wave resonances and time-dependent wave motion in stratified fluid with permeable bottom

A Strange Result Regarding Some MHD Motions of Generalized Burgers’ Fluids with a Differential Expression of Shear Stress on the Boundary

In this work, we investigate isothermal MHD motions of a large class of rate type fluids through a porous medium between two infinite horizontal parallel plates when a differential expression of the non-trivial shear stress is prescribed on the boundary. Exact expressions are provided for the dimensionless steady state velocities, shear stresses and Darcy’s resistances. Obtained solutions can be used to find the necessary time to touch the steady state or to bring to light certain characteristics of the fluid motion. Graphical representations showed the fluid moves slower in presence of a magnetic field or porous medium. In addition, contrary to our expectations, the volume flux across a plane orthogonal to the velocity vector per unit width of this plane is zero. Finally, based on a simple remark regarding the governing equations of velocity and shear stress for MHD motions of incompressible generalized Burgers’ fluids between infinite parallel plates, provided were the first exact solutions for MHD motions of these fluids when the two plates apply oscillatory or constant shear stresses to the fluid. This important remark offers the possibility to solve any isothermal MHD motion of these fluids between infinite parallel plates or over an infinite plate when the non-trivial shear stress is prescribed on the boundary. As an application, steady state solutions for MHD motions of same fluids have been developed when a differential expression of the fluid velocity is prescribed on the boundary.