Motion Of Fluid Particles Research Articles

Homogeneous–heterogeneous reactions for Maxwell nanofluid flow over an elongating cylindrical pipe via finite element method

AbstractHomogeneous–heterogeneous chemical reactions in simultaneous heat and mass transport for Maxwell fluid subjected to thermophoresis and Brownian motion are modeled and governing mathematical models are simplified using approximations proposed models are simplified using approximations proposed by Ludwing Prandtl. The simplified governing mathematical models under Buongiorno's theory are numerically solved via finite element method (FEM). The convergence and mesh free solution are solved for parametric study. The momentum relaxation phenomenon is the characteristic of liquid to restore its equilibrium state. Therefore, a remarkable reduction in the motion of fluid particles against an increase in Deborah number is noticed. A rise in temperature distribution is noticed when Brownian motion parameter is enhanced. The flow is decelerated as the curvature of the cylinder increases. As a consequence, the viscous region shrinks and its thickness becomes smaller. Hence, it is concluded that flow over flat surface has wider boundary layer region than the boundary layer region associated with flow over the cylindrical surface. The wall shear stress for the flow over a cylindrical object is higher than that for the flow over a flat surface. The wall heat and mass fluxes have an increasing tendency when the curvature parameter is increased. Wall heat flux and wall mass flux have opposite behavior due to rise in thermophorsis and Brownian motion effects.

Computational study on magnetohydrodynamics heat and mass transport in polymeric liquid using micropolar theory of fluids

Theory of Eringen for polymer fluid, called micropolar fluid, has revealed that if micro-solid structures or nano-sized solid bodies are immersed in polymers, then vortex and spin gradient effects become significant and the flow of such polymers cannot be modeled by the usual Newtonian rheological model or non-Newtonian model which do not capture vortex and spin gradient effects due to couple stress exerted by nano- or microstructures. Thus this manuscript uses Eringen's theory and generalized Fourier law for modeling of flows and related mechanisms like heat and mass transfer. Models are solved numerically and simulations are visualized. The different samples of parametric values are chosen during numerical experiments and outcomes are examined. The mass flux has shown an increasing behavior versus vortex motion of fluid particles due to raise in convective transport of mass of solute. It is also found that mass flux in hybrid nanopolymers is less than that in mono nanopolymers. Magnetic field intensity is directly proportional to the mass flux and therefore, an increase in mass flux due to an increase in Hartmann number is observed. Solutal relaxation time has shown an increasing behavior on the mass flux.

Lagrangian analysis of the flow induced by a dielectric barrier discharge plasma actuator array under burst mode actuation

The dynamic properties of the flow induced by a dielectric barrier discharge (DBD) plasma actuator array are investigated from the Lagrangian perspective. First, numerical simulations based on a body force model are performed to obtain the flow field induced by unsteady plasma actuation in the burst mode. The numerical simulations capture the flow characteristics of plasma actuation well. Subsequently, the ridges of the finite-time Lyapunov exponent field are employed to identify the Lagrangian coherent structures (LCSs). Both the attracting and repelling LCSs organize the plasma-induced flow’s dynamic behaviors. The attracting LCSs visualize the plasma-induced vortices. The vortex formation, development, and merging processes in the unsteady plasma actuation are resolved well by the LCSs. The material transport in the plasma-induced flow is analyzed by tracing the fluid particle motions. Then, the influences of the actuation parameters, duty cycle, and burst frequency on the flow structures are explored via the attracting LCSs. The presented results enhance the understanding of plasma actuation flow physics and promote the optimal use of DBD plasma actuator arrays.

CHAOTIC BEHAVIOR OF MODIFIED STRETCH–TWIST–FOLD FLOW UNDER FRACTAL-FRACTIONAL DERIVATIVES

The application of the recently proposed integral and differential operators known as the fractal-fractional derivatives and integrals has opened doors to ongoing research in different fields of science, engineering, and technology. These operators are a convolution of the fractal derivative with the generalized Mittag-Leffler function with Delta-Dirac property, the power law, and the exponential decay law with Delta-Dirac property. In this paper, we aim to extend the work in the literature by applying these operators to a modified stretch–twist–fold (STF) flow based on the STF flow related to the motion of particles in fluids that naturally occur in the dynamo theorem. We want to capture the dynamical behavior of the modified STF flow under these operators. We will present the numerical schemes that can be used to solve these nonlinear systems of differential equations. We will also consider numerical simulations for different values of fractional order and fractal dimension.

A numerical approach for fluid-particle-structure interactions problem with CFD-DEM-CSD coupling method

Fluid, particle, and structure interactions are widely encountered in the engineering field. This study presents a multi-phase coupled method based on computational fluid dynamics (CFD), discrete element method (DEM) and computational structural dynamics (CSD) for simulating fluid, particle and structure interactions problems (FPSI). For the proposed CFD-DEM-CSD coupling method, the CFD-DEM method based on locally averaged theory is applied to capture the motion of the fluid-particle flow, and the CSD method within the finite volume method (FVM) is used to resolve the deformation of the structure. The proposed coupling method is first tested by simulating a classical fluid–structure interaction problem (FSI3) and an upward seepage flow through sand. Then, the process of water and particle leakage through a crack affected by an immersed elastic plate is analyzed by both the laboratory experiment and the proposed numerical method. The particle motions and elastic plate deformation obtained from both methods show good agreement, which verifies the performance of the proposed method. The developed CFD-DEM-CSD method can be used to acquire in-depth knowledge of the fluid state, particle motions and structural deformation of the fluid, particle and structure system.

An improved lattice Boltzmann model for fluid–fluid–solid flows with high viscosity ratio

In this paper, we present an improved lattice Boltzmann model for fluid–fluid–solid (FFS) flows with a high viscosity ratio. The bounce-back particle model is combined with the Shan–Chen (SC) multicomponent model. We extend the bounce-back scheme based on velocity interpolation and a fresh-node initialization approach with second-order accuracy to moving particles within the framework of the multicomponent model. An improved virtual solid density model for wetting boundary conditions is employed to implement contact angles on curved boundaries. We examine the factors that lead to the violation of mass conservation, and an easy redistributing method is developed to fix the mass leakage issue. The combined multiphase particle model is able to simulate FFS flows with a high viscosity ratio of up to 1000 while preserving the total mass of the two fluids. The performance of the approach is tested by a variety of numerical experiments. The dynamic behaviors of moving contact lines on the curved boundary are validated by a droplet wetting on a solid particle. The model is then applied to simulate dynamic FFS problems, such as particle wetting at the fluid interface and particle motion through a fluid–fluid interface. According to the simulation results, the present model is capable of capturing the total force exerted on a particle by the fluid and the interface. However, the SC-type fluid–solid interaction force does not equal the capillary force in the present model. Finally, the self-assembly process of two floating particles on a liquid–liquid interface is investigated.

Experiments on the Drag and Lift Coefficients of a Spinning Sphere

The drag and lift coefficients are important parameters that affect the particle motion in a viscous fluid. In the present study, the drag and lift coefficients of a spinning sphere in a water tank were studied experimentally using a high-speed camera. To this end, 22 cases were studied to cover a wide range of dimensionless angular speeds (0.149 < Rr < 3.471) and Reynolds numbers (610 < Re < 3472). Based on the present experimental data and the results obtained from the literature, expressions were developed to calculate the lift and drag coefficients. The performed analyses on lift coefficient show that there is a critical Reynolds number (Rec) at each dimensionless angular speed. When 0 < Re < Rec, the lift coefficient decreases with increasing the Reynolds number, while it is constant when Rec < Re< 3500. The constant lift coefficient corresponding to different spin speeds was defined as the limit value of the lift coefficient. It is found that when 1 < Rr < 12, the limit value of the lift coefficient is 0.37, while the limit value of the lift coefficient increases with increasing dimensionless angular speed at 0 < Rr < 1. It is found that the spin increases the drag coefficient of a spinning sphere only when 0 < Rr < 10. Moreover, the performed analyses show that the drag coefficient of a spinning sphere is less than that of a non-spinning sphere when 10 < Rr < 25. Furthermore, the lift-to-drag ratio of a spinning sphere is discussed in this article.

Flow dynamics for coupled surface and internal deep-water waves

This article determines the fluid motion underlying coupled linear internal and surface waves in a deep-water two-fluid-layer model (with the lower layer being of infinite depth). A detailed Eulerian description of the wave-field kinematics for coupled linear travelling waves is achieved using phase-plane analysis. The qualitative motion of individual fluid particles is elucidated through analysis of the relevant nonlinear dynamical systems from the Lagrangian viewpoint.

Stability of a Nonlinear ML-Nonsingular Kernel Fractional Langevin System with Distributed Lags and Integral Control

The fractional Langevin equation has more advantages than its classical equation in representing the random motion of Brownian particles in complex viscoelastic fluid. The Mittag–Leffler (ML) fractional equation without singularity is more accurate and effective than Riemann–Caputo (RC) and Riemann–Liouville (RL) fractional equation in portraying Brownian motion. This paper focuses on a nonlinear ML-fractional Langevin system with distributed lag and integral control. Employing the fixed-point theorem of generalised metric space established by Diaz and Margolis, we built the Hyers–Ulam–Rassias (HUR) stability along with Hyers–Ulam (HU) stability of this ML-fractional Langevin system. Applying our main results and MATLAB software, we have carried out theoretical analysis and numerical simulation on an example. By comparing with the numerical simulation of the corresponding classical Langevin system, it can be seen that the ML-fractional Langevin system can better reflect the stationarity of random particles in the statistical sense.

A generalised drift-correcting time integration scheme for Brownian suspensions of rigid particles with arbitrary shape

The efficient computation of the overdamped, random motion of micron and nanometre scale particles in a viscous fluid requires novel methods to obtain the hydrodynamic interactions, random displacements and Brownian drift at minimal cost. Capturing Brownian drift is done most efficiently through a judiciously constructed time-integration scheme that automatically accounts for its contribution to particle motion. In this paper, we present a generalised drift-correcting (gDC) scheme that accounts for Brownian drift for suspensions of rigid particles with arbitrary shape. The scheme seamlessly integrates with fast methods for computing the hydrodynamic interactions and random increments and requires a single full mobility solve per time-step. As a result, the gDC provides increased computational efficiency when used in conjunction with grid-based methods that employ fluctuating hydrodynamics to obtain the random increments. Further, for these methods the additional computations that the scheme requires occur at the level of individual particles, and hence lend themselves naturally to parallel computation. We perform a series of simulations that demonstrate the gDC obtains similar levels of accuracy as compared with the existing state-of-the-art. In addition, these simulations illustrate the gDC's applicability to a wide array of relevant problems involving Brownian suspensions of non-spherical particles, such as the structure of liquid crystals and the rheology of complex fluids.

Numerical study on thermal enhancement in magnetohydrodynamic micropolar liquid subjected to motile gyrotactic microorganisms movement and Soret and dufour effects

Motile gyrotactic organism activity in micropolar fluid subjected to simultaneous heat and mass transfer in the presence of thermal diffusion and diffusion thermo effects is modeled. The base fluid is taken as kerosene oil. The immersion of nano-sized particles of C u − T i O 2 kerosene oil makes its rheological characteristics of micropolar fluid because nano-sized particles serve as micro-structures. In this case couple stress, vortex and spin gradient viscosities become significant and simultaneously linear and angular momenta become equally remarkable. So, micropolar theory is the best to model the immersion of nano-structures in the fluid. Similarity variables are used to transform the problems into their dimensionless forms. The mathematical models are solved numerically by applying the finite element method (FEM). The results are validated and numerical experiments are performed to analyze the key parameters of the unknown field variables. In order to analyze the impact of physical parameters on field variables, numerous simulations are performed. The micro-rotation of microparticles and nanoparticles due to fluid deformation motivates fluids particles to rotate faster. Therefore, linear motion is observed to be increased for higher values of vortex viscosity. The curvature parameter has significantly impacted the linear motion of the fluid particles. The impact of the curvature parameter on the movement of nanofluid is lesser than the impact of the curvature parameter on the motion of hybrid nanoparticles. Concentration gradient supports the diffusion of heat in the fluid regime and numerical experiments with variation of Dufour (that measures the effects of concentration gradient on heat diffusion) have shown that concentration gradient is more effective in the case of hybrid nanofluid relative to the mono nanofluid. The angular motion of fluid particles increases when vortex viscosity is increased. Numerical simulations have predicted that the angular motion of particles of hybrid nanofluid has a lesser angular speed than that of the angular motion of particles of mono nanofluid. The Soret number determines the impact of temperature gradient on the diffusion of solute in the fluid. Simulations for various values of Soret number have predicted that the impact of temperature gradient on the diffusion of solute in hybrid nanofluid is stronger than the impact of temperature gradient on the diffusion of solute in mono nanofluid.

Numerical simulations of polygonal particles settling within non-Newtonian fluids

The settling of circular and polygonal particles within non-Newtonian fluids is investigated by combining the lattice Boltzmann method (LBM) and the discrete element method (DEM). The immersed moving boundary (IMB) scheme with good numerical stability is adopted to couple LBM and DEM. To efficiently calculate the solid coverage ratio in IMB, a novel method is developed, which simply involves judging whether the square is fully occupied by the particle and subdividing the square crossed by the fluid–solid boundary. After validations, the drafting–kissing–tumbling dynamics of two particles settling in the Newtonian and power-law fluids are studied first. It shows that the shear-thickening fluid has a longer kissing duration than the Newtonian and shear-thinning fluids. The kissing duration of squared particles (0.29–0.41 s) is shorter than triangular particles (0.32–0.84 s) and much shorter than circular particles (0.61–0.98 s). Then, the settling of multiple and multi-shape particles in a closed cavity is analyzed. The disturbed area of kinematic viscosity induced by particle motion in the shear-thinning fluid is 21.0–22.5 cm2, significantly larger than in the shear-thickening fluid (10.1–10.8 cm2). Circular particles have a larger disturbed area than the polygonal particles due to the larger settling velocity. Moreover, compared with the Newtonian and shear-thinning fluids, the shear-thickening fluid has a smaller vertical length of particle cluster, meaning a positive influence on the agglomeration of particles.

CFD-DEM based wind-deposited sand high concentration slurry pipe transport characteristics and erosion study

In order to study the conveying process of wind-accumulated sand slurry pipeline, this study simulates the flow process of wind-accumulated sand slurry at 1m/s inlet flow rate with straight pipe bend and uphill by coupled CFD-DEM method. The fluid flow, particle motion and position distribution, pipe erosion and force during the whole process are analyzed based on the selection of a suitable traction model. The results show that the flow velocity of highly viscous slurry at the wall of the pipe is small which can easily lead to the deposition of sand particles, which is proved by the particle velocity cloud diagram. The extent of erosion and the degree of erosion increase with time, and the peak of erosion occurs at the bend. The force changes along the Y-direction in different parts of the pipe show that the extreme values of force and erosion are located at the bend. This part is the weak point of the whole pipeline slurry flow and erosion project should pay attention to reinforcement or monitoring.

Active Brownian motion with memory delay induced by a viscoelastic medium

By now active Brownian motion is a well-established model to describe the motion of mesoscopic self-propelled particles in a Newtonian fluid. On the basis of the generalized Langevin equation, we present an analytic framework for active Brownian motion with memory delay assuming time-dependent friction kernels for both translational and orientational degrees of freedom to account for the time-delayed response of a viscoelastic medium. Analytical results are obtained for the orientational correlation function, mean displacement, and mean-square displacement which we evaluate in particular for a Maxwell fluid characterized by a kernel which decays exponentially in time. Further, we identify a memory-induced delay between the effective self-propulsion force and the particle orientation which we quantify in terms of a special dynamical correlation function. In principle, our predictions can be verified for an active colloidal particle in various viscoelastic environments such as a polymer solution.

Numerical study on non-Fourier heat and mass transfer in partially ionized MHD Williamson hybrid nanofluid

This article aims to analyze the combined effects of Hall and ion slip currents, Darcy-Forchheimer porous medium, and non-uniform magnetic field under the suspension of hybrid nanoparticles. The flow situation is transformed into mathematical problems using conservation laws and correlations among thermophysical properties of base fluid nano and hybrid nanoparticles. These mathematical models are approximated under boundary layer (BL) approximations. The similarity analysis is performed and the finite element method (FEM) is deployed for the simulations and further investigations regarding non-Fourier behavior of heat and mass transfer. The present results have good agreement with the published benchmark which is a special case of present work. The numerical simulations for the motion of fluid particles under the variation of Weissenberg number are observed and it is noticed that fluid motion decelerates for higher values of Weissenberg number. Significant retardation to the motion of the fluid is seen because of an increase in the Darcy porous medium parameter as an increase in it implies a decrease in the permeability of the porous. Thermal relaxation is the property of the fluid due to which it avoids thermal changes to maintain thermal equilibrium. Therefore, a remarkable decrease in the temperature of fluid exhibiting thermal relaxation characteristics is noticed. It is also noted from numerical experiments that Hall and ion slip currents are responsible to slow down the Ohmic dissipation phenomenon. Thus the property of ionized fluid helps in controlling the thickness of thermal BL. Numerical experiments have shown that the solutal relaxation time for hybrid nanofluid is greater than that for mono nanofluid. Mass diffusivity of the fluid with hybrid nanofluid is less than that of mono nanofluid.

On the Topology of the Atmosphere Advected by a Periodic Array of Axisymmetric Thin-cored Vortex Rings

The fluid motion produced by a periodic array of identical, axisymmetric, thin-cored vortex rings is investigated. It is well known that such an array moves uniformly without change of shape or form in the direction of the central axis of symmetry, and is therefore an equilibrium solution of Euler's equations. In a frame of reference moving with the system of vortex rings, the motion of passive fluid particles is investigated as a function of the two non-dimensional parameters that define this system: $\varepsilon = a/R$, the ratio of minor radius to major radius of the torus-shaped vortex rings, and $\lambda = L/R$, the separation of the vortex rings normalized by their radii. Two bifurcations in the streamline topology are found that depend significantly on $\varepsilon$ and $\lambda$; these bifurcations delineate three distinct shapes of the 'atmosphere' of fluid particles that move together with the vortex ring for all time. Analogous to the case of an isolated vortex ring, the atmospheres can be 'thin-bodied' or 'thick-bodied'. Additionally, we find the occurrence of a 'connected' system, in which the atmospheres of neighboring rings touch at an invariant ring of fluid particles that is stationary in a frame of reference moving with the rings.

Computational analysis for enhancement of heat and mass transfer in MHD-polymer with hybrid nano-particles using generalized laws

Novel models for heat flux with laws of linear and angular momenta and convection-diffusion equation for heat are used for the formulation of system of problems associated with the flow of polymer (micropolar fluid) over a cylindrical heated body elongating in a radial direction with non-uniform velocity. Spin gradient and vortex effects with couple stresses are taken into account. Problems are solved using the finite element method (FEM) with Galerkin approximation. Grid-independent and convergent solutions are derived. The results for special cases are compared and validated with published benchmarks. Simulations are used to assess the impact of parameters on flow variables based on the convergent solutions. Simulated results are displayed in the form of velocity, temperature and concentration graphs. Thermal relaxation time corresponds to thermal elastic behaviour and is responsible to make the fluid to restore the thermal equilibrium. This thermal relaxation phenomenon helps in reducing the width of the thermal region. The angular motion of fluid particles has been shown to be affected less by vortex viscosity. Vortex viscosity has shown a greater impact on the motion of Cu−Ag− polymer relative that on Cu− polymer. Thermal performance of Cu−Ag− polymer is better than the thermal enhancement of Cu− polymer. Due to Joule heating, hybrid nanofluid dissipates more heat relative to the nanofluid. Vortex viscosity plays vital role in controlling the thermal region. Heat flux has shown an increase as a function of thermal relaxation time.

Unsteady and lineal translation of a sphere through a viscoelastic fluid

Unsteady translation of a sphere in a viscoelastic fluid is studied analytically. General, fully invertible relationships between an imposed time-dependent velocity and the resultant force are described in terms of a Volterra series expansion. These results are used to analyze particle motion in fluids described by the Johnson-Segalman and Giesekus models and to define a general framework for analyzing weakly nonlinear microrheology measurements.

Stability of a Nonlinear Fractional Langevin System with Nonsingular Exponential Kernel and Delay Control

Fractional Langevin system has great advantages in describing the random motion of Brownian particles in complex viscous fluid. This manuscript deals with a delayed nonlinear fractional Langevin system with nonsingular exponential kernel. Based on the fixed point theory, some sufficient criteria for the existence and uniqueness of solution are established. We also prove that this system is UH‐ and UHR‐stable attributed to the nonlinear analysis and inequality techniques. As applications, we provide some examples and simulations to illustrate the availability of main findings.

Multiscale CFD simulation of biomass fast pyrolysis with a machine learning derived intra-particle model and detailed pyrolysis kinetics

Coupling particle and reactor scale models is as essential as reactor fluid dynamics and particle motion for accurate Computational Fluid Dynamic (CFD) simulations of biomass fast pyrolysis reactors due to intraparticle heat transfer and chemical reactions controlling conversion time and product distributions. Direct online coupling of a particle model with a reactor model is computationally expensive, while offline coupling is case-dependent. In this research, solutions from a series of particle pyrolysis simulations were regressed with Artificial Neural Network (ANN). This machine learning-derived model predicted the same temperature and conversion profiles compared with particle resolved simulation while the isothermal approach overpredicted the temperature by 130 K and underpredicted the conversion time by 30 s. The ANN model was then integrated into CFD simulations of fluidized bed biomass fast pyrolysis with varied feedstocks via coupling PyTorch and MFiX. The averaged error of simulation predicted bio-oil yields with four feedstocks is 6.4%. This multi-scale approach provides an efficient tool for the coupled particle and reactor scale simulations of biomass pyrolysis.