Couette Channel Research Articles

Effectiveness of silver-magnesium oxide-water hybrid nanofluid in Couette channel

The present article numerically investigates the unsteady magnetohydrodynamic (MHD) Couette flow containing novel (Ag + MgO)-water hybrid nanofluid (HNF). The nanoparticles of silver (Ag) and magnesium oxide (MgO) are supplemented to base fluid water. The top wall is kept in uniform motion while the bottom wall of channel set stationary and stretchable. An external magnetic field is applied perpendicular to lower plate. The governed nonlinear partial differential equations (PDE) are solved employing finite difference method (FDM). The effects of hybrid nanofluid and nanofluid (NF) are compared for the significant parameters and presented graphically. The results illustrate that (Ag + MgO)-water HNF exhibits significant influence over Ag-water NF on velocity and temperature in the Couette channel.

Effects of Ohmic heating, induced magnetic field and Newtonian heating on magnetohydrodynamic generalized Couette flow of Jeffrey nanofluid between two parallel horizontal plates with convective cooling

In this article, the effects of Ohmic heating, induced magnetic field and Newtonian heating on MHD generalized Couette flow of Jeffrey nanofluid between two horizontal plates with convective cooling has been investigated. The mathematical model used for the magnetohydrodynamic generalized Couette flow of pure water as the fluid phase containing Copper (Cu) as nanoparticles takes into account the effects of viscous dissipation, Soret and Dufour. The numerical solution of the system of nonlinear partial differential equations controlling the flow was performed using the finite difference method. To acquire the flow variable profiles, such as velocity, induced magnetic field, temperature, and concentration profiles graphically, the resulting numerical schemes are simulated in MATLAB software. The findings reveal that an increase in the Schmidt number causes a decrease in the concentration profiles, rise in the Jeffrey parameter causes a decrease in the velocity profiles. The temperature profiles also rise as a result of an increase in the Ohmic heating parameter and the heat generation parameter. Induced magnetic field profiles decreases with an increase in magnetic Prandtl number. The results demonstrate that Cu - water shows significant impact over nanofluid on temperature and velocity in the generalized Couette channel. The results of this study are valuable because they can be applied to the development of many chemical technologies, such as the production of polymers, MHD pumps, food processing, chemical catalytic reactors, MHD flow meters, astronomy, and lubrication. The results are compared with standard literature and show good agreement.

Thermo-fluidic transport process in magnetohydrodynamic Couette channel containing hybrid nanofluid

Current paper focusses on the mathematical simulation of thermo-fluidic unsteady flow in a magnetohydrodynamic (MHD) Couette channel containing novel (ZnO–Al2 O3)-water hybrid nanofluid (HNF). The nanoparticles of zinc oxide(ZnO) and aluminium oxide(Al2O3) are supplemented to basefluid water in 1:1 ratio. The bottom wall of channel kept stationary and stretchable, while the top is set in uniform motion with convective cooling. A uniform magnetic field appealed normally to lower plate. The governed nonlinear partial differential equations(PDE) are integrated employing finite difference method (FDM). A comparison of effect of hybrid nanofluid versus nanofluid (NF) is performed. The effects of non-dimensional quantities namely, nanoparticle volume fraction(NVF), magnetic field, stretching parameter, Biot number and Eckert number are reported graphically. The results demonstrate that (ZnO+ Al2O3)-water HNF shows significant impact over ZnO–water NF on velocity and temperature in the Couette channel.

Influence of Exponential Space Based Heat Source on Unsteady Couette Nanoliquid Flow

Present article addresses unsteady Couette flow of nanofluid constricted Couette channel under the impression of exponential space based heat source (ESHS) and temperature based heat source (THS). The novelty of the study is to combine the effects of heat sources of type ESHS and THS to the Couette flow. The governed flow equations are solved employing FEM. The influence of dimensionless quantities such as ESHS, Biot number, variable viscosity and stretching parameter are exposed graphically. From the attained outcomes, it is observed that the profile of temperature rather than the velocity, in the Couette channel is boosted with ESHS and THS parameters.

Numerical Solution of Transient Fe3O4-EG Nanofluid Flow past Couette Channel Associated with Radiation

The aim of the present paper is to analyze the transient Couette nanofluid flow of ethylene glycol(EG)-Ferrous oxide(Fe3O4) between two parallel plates in the presence of thermal radiation. Tiwari and Das nanofluid model is assumed to frame the governing equations. The novelty of the study is combining the effects of thermal radiation and Couette flow with pulsative pressure gradient. It is important because of its applications in the lubricant technology and advanced energy conversion systems operated at high temperature. The effects of dimensionless quantities such as radiation parameter(Rd=0.1 – 0.5), Biot number(Bi=1 4), nanoparticle volume fraction(), pressure gradient(A=1 3), amplitude pulse() stretching parameter() and viscosity variation parameter() are explored graphically. The main conclusion that can be drawn from the results is that high velocity region of steady state is strengthened near the upper plate with the growth in stretching parameter rather thermal radiation. The temperature near the upper plate enhances with thermal radiation. A vortex is formed in the upper half region of Couette channel with the increase in the phase angle, amplitude and pressure gradient. The temperature in the upper region of Couette channel, is significantly enhanced by the volume fraction of nanoparticles.

On-wall and interior separation in a two-fluid boundary layer

A two-fluid boundary layer is considered in the context of a high Reynolds number Poiseuille–Couette channel flow encountering an elongated shallow obstacle. The flow is laminar, steady and two-dimensional, with the boundary layer shown to have the pressure unknown in advance and a specified displacement (a condensed boundary layer). The focus is on the detail of the flow reversal triggered by the obstacle. The interface between the two fluids passes through the boundary layer which, in conjunction with the effects of gravity and distinct densities in the two fluids, leads to several possible topologies of the reversed flow, including a conventional on-wall separation, interior flow reversal above the interface, and several combinations of the two. The effect of upstream influence due to a transverse pressure variation under gravity is mentioned briefly.

Thermal Radiation, Chemical Reaction, Viscous and Joule Dissipation Effects on MHD Flow Embedded in a Porous Medium

An analysis is presented to study the effects of thermal radiation, chemical reaction, viscous and Joule dissipation on MHD free convection flow between a pair of infinite vertical Couette channel walls embedded in a porous medium. The fluid flows by a strong transverse magnetic field imposed perpendicularly to the channel wall on the assumption of a small magnetic Reynolds number. The governing non linear partial differential equations are transformed in to ordinary differential equations and are solved analytically. The effect of various parameters viz., Eckert number, electric conductivity, dynamic viscosity and strength of magnetic field on temperature profile has been discussed and presented graphically.

Effect of Thermal Radiation, Chemical Reaction and Viscous Dissipation on MHD Flow

This study examines the effect of thermal radiation, chemical reaction and viscous dissipation on a magnetohydro- dynamic flow in between a pair of infinite vertical Couette channel walls. The momentum equation accounts the effects of both the thermal and the concentration buoyancy forces of the flow. The energy equation addresses the effects of the thermal radiation and viscous dissipation of the flow. Also, the concentration equation includes the effects of molecular diffusivity and chemical reaction parameters. The gray colored fluid considered in this study is a non-scattering medium and has the property of absorbing and emitting radiation. The Roseland approximation is used to describe the radiative heat flux in the energy equation. The velocity of flow transforms kinetic energy into heat energy. The increment of the velocity due to internal energy results in heating up of the fluid and consequently it causes increment of the thermal buoyancy force. The Eckert number being the ratio of the kinetic energy of the flow to the temperature difference of the channel walls is directly proportional to the thermal energy dissipation. It can be observed that increasing the Eckert number results in increasing velocity. A uniform magnetic field is applied perpendicular to the channel walls. The temperature of the moving wall is high enough due to the presence of thermal radiation. The solution of the governing equations is obtained using regular perturbation techniques. These techniques help to convert partial differential equations to a set of ordinary differential equations in dimensionless form and thus they are solved analytically. The following results are obtained: from the simulation study it is observed that the flow pattern of the fluid is affected due to the influence of the thermal radiation, the chemical reaction and viscous dissipation. The increment in the Hartmann number results in the increment of the Lorentz force but a decrement in velocity of the flow. An increment in the radiative parameter results in a decrement in temperature. An increment in the Prandtl number results in a decrement in thermal diffusivity. An increment in both the chemical reaction parameter and molecular diffusivity results in a decrement in concentration.

Peripheral mixing of passive scalar at small Reynolds number

Mixing of a passive scalar in the peripheral region close to a wall is investigated by means of accurate direct numerical simulations of both a three-dimensional Couette channel flow at low Reynolds numbers and a two-dimensional synthetic flow. In both cases, the resulting phenomenology can be understood in terms of the theory recently developed by Lebedev & Turitsyn (Phys. Rev. E, vol. 69, 2004, 036301). Our results prove the robustness of the identified mechanisms responsible for the persistency of scalar concentration close to the wall with important consequences in completely different fields ranging from microfluidic applications to environmental dispersion modelling.

Geometrical properties of the vorticity vector derived using large-eddy simulation

In this paper, the geometrical properties of the resolved vorticity vector ω ¯ derived from large-eddy simulation are investigated using a statistical method. Numerical tests have been performed based on a turbulent Couette channel flow using three different dynamic linear and nonlinear subgrid-scale stress models. The geometrical properties of ω ¯ have a significant impact on various physical quantities and processes of the flow. To demonstrate, we examined helicity and helical structure, the attitude of ω ¯ with respect to the eigenframes of the resolved strain rate tensor S ¯ ij and negative subgrid-scale stress tensor - τ ij , enstrophy generation, and local vortex stretching and compression. It is observed that the presence of the wall has a strong anisotropic influence on the alignment patterns between ω ¯ and the eigenvectors of S ¯ ij , and between ω ¯ and the resolved vortex stretching vector. Some interesting wall-limiting geometrical alignment patterns and probability density distributions in the form of Dirac delta functions associated with these alignment patterns are reported. To quantify the subgrid-scale modelling effects, the attitude of ω ¯ with respect to the eigenframe of - τ ij is studied, and the geometrical alignment between ω ¯ and the Euler axis is also investigated. The Euler axis and angle for describing the relative rotation between the eigenframes of - τ ij and S ¯ ij are natural invariants of the rotation matrix, and are found to be effective for characterizing a subgrid-scale stress model and for quantifying the associated subgrid-scale modelling effects on the geometrical properties of ω ¯ .

LES of turbulent heat transfer in Couette channel flow using dynamic SGS models

The present paper documents a Large Eddy Simulation of thermal transport in turbulent Couette flow with a constant wall temperature difference. A local formulation of a dynamic eddy viscosity model is used to model the subgrid-scale (SGS) stress, while the SGS heat flux is calculated two ways: • using the dynamic eddy viscosity and a constant SGS Prandtl number • using a second dynamic formulation for the SGS Prandtl number. Both simulations capture important features of the temperature field, although some small differences exist. Implementation of the dynamic SGS Prandtl number in a local formulation required extreme levels of clipping to ensure numerical stability.

Penetration of Shear Flow Into an Array of Rods Aligned With the Flow

AbstractShear flow over a square array of widely‐spaced rods aligned with the flow is investigated using singularity methods to solve Stokes equation. The flow field is determined for various arrays occupying a fraction of a Couette channel, for solid volume fractions from 0.001 to 0.1. Flow penetration into an array is quantified by the slip velocity at the array edge. This velocity is much greater than when the flow is across the array but still less than the value predicted by the use of Brinkman's equation.

A hybrid spectral/boundary‐integral approach for transient viscoelastic flow exiting a channel

A hybrid spectral/boundary element approach is proposed to examine the influence of Couette channel flow on transient coating of highly elastic fluids. The viscoelastic instability of one‐dimensional plane Couette flow is first determined for a large class of Oldroyd fluids with added viscosity, which typically represent polymer solutions composed of a Newtonian solvent and a polymeric solute. The Johnson‐Segalman equation is used as the constitutive model. The velocity profile inside the channel is taken as the exit profile for the emerging free‐surface flow. The flow is assumed to be Newtonian as it emerges from the channel. An estimate of the magnitude of the rate‐of‐strain tensor components in the free‐surface region reveals that they are generally smaller than the shear rate inside the channel. The evolution of the flow front is simulated using the boundary element method. For the channel flow, the problem is reduced to a non‐linear dynamical system using the Galerkin projection method. Stability analysis indicates that the channel velocity may be linear or non‐linear depending on the range of the Weissenberg number. The evolution of the coating flow at the exit is examined for steady as well as transient (monotonic and oscillatory) channel flow. It is found that adverse flow can exist as a result of fluid elasticity, which can hinder the process of blade coating.

Viscous resuspension of a sediment caused by oscillating stratified flows

It is known that a sediment of settled particles can resuspend under the action of shear. In this paper, based on a mathematical model given by Leighton and Acrivos [6], we study theoretically the viscous resuspension of a sediment in a Couette channel with harmonically oscillating walls. Numerical experiments reveal that the resuspension height and the particle volume concentration at the bottom of the channel depend on the frequency of the oscillation. While oscillation of the top wall has nearly no influence on the sediment, a moving bottom wall causes the settled particles to completely resuspend if the frequency is large enough.

Turbulence, scalar transport, and reaction rates in flame-wall interaction

Turbulent premixed flames are studied in a Couette channel flow using direct numerical simulation (DNS). The combustion is simulated by a single-step reaction with heat release, and the flow is fully developed turbulence at a Reynolds number of 504 based on channel half-width The flow configuration consists of a V-shaped flame held in place by a flame holder. One flame is far from the walls and remains adiabatic, while the other flame interacts with a wall and is nonadiabatic. The flame alters the turbulent velocity profile. Near-wall viscous sublayer scaling is found provided both the pressure gradient and the local, average wall shear stress are used. However, in the log layer, the standard scaling does not collapse the velocity profiles, indicating the importance of additional transport mechanisms caused by the flame. The turbulent length scale is reduced in the flame brush region. In the adiabatic flame, the reduction is to approximately the laminar flame thickness. In the nonadiabatic wall flame, the reduction is not as dramatic due to wall heat loss causing weaker reaction rates. The probability density function (PDF) of the scalar progress variable has a classical bi-modal shape in the adiabatic flame. Thus, in the adiabatic flame, the DNS results compare well with the standard Bray-Moss-Libby (BML) expressions for the turbulent scalar flux and flame surface density. However, in the nonadiabatic flame, which interacts with the wall, the scalar PDF is less bi-modal. In this case, the DNS results and the BML expression for the flame surface density does not correctly capture the heat loss effects of the wall. Modifications to the flame surface area are suggested and compare well with the DNS results.

Structure parameters in rotating Couette-Poiseuille channel flow

It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.

Experiments on Plane Couette Flow

A simple method for generating plane Couette flow is described. In this technique the water surface of a covered open-channel flume represents the moving boundary, and measurements are performed in the overlying (sandwiched) air layer. Experimental results are presented which suggest transition from laminar to turbulent plane Couette flow at a Reynolds number (based on center-line velocity and channel half-depth) of about 280. Turbulent mean velocities from all available sources are correlated in terms of inner and outer law coordinates, and universal skin friction laws are derived therefrom for the case of hydrodynamically smooth boundaries. However, it is concluded that none of the presently available experimental data on turbulent plane Couette flow render support for von Kármán's theory of homologous turbulence. Results of a cursory exploration of the effects of unilateral boundary roughness suggest that mean-flow characteristics on the smooth side of a Couette channel assume the features prevailing on the rough side.