Showing papers on "Hartmann number published in 2012"

Analytical investigation of Jeffery-Hamel flow with high magnetic field and nanoparticle by Adomian decomposition method

Abstract: In this study, the effects of magnetic field and nanoparticle on the Jeffery-Hamel flow are studied using a powerful analytical method called the Adomian decomposition method (ADM). The traditional Navier-Stokes equation of fluid mechanics and Maxwell’s electromagnetism governing equations are reduced to nonlinear ordinary differential equations to model the problem. The obtained results are well agreed with that of the Runge-Kutta method. The present plots confirm that the method has high accuracy for different α, Ha, and Re numbers. The flow field inside the divergent channel is studied for various values of Hartmann number and angle of channel. The effect of nanoparticle volume fraction in the absence of magnetic field is investigated.

Numerical study of magnetohydrodynamic duct flow at high Reynolds and Hartmann numbers

Abstract: High-resolution direct numerical simulations are conducted to analyse turbulent states of the flow of an electrically conducting fluid in a duct of square cross-section with electrically insulating walls and imposed transverse magnetic field. The Reynolds number of the flow is and the Hartmann number varies from to . It is found that there is a broad range of Hartmann numbers in which the flow is neither laminar nor fully turbulent, but has laminar core, Hartmann boundary layers and turbulent zones near the walls parallel to the magnetic field. Analysis of turbulent fluctuations shows that each zone consists of two layers: the boundary layer near the wall characterized by small-scale turbulence and the outer layer dominated by large-scale vortical structures strongly elongated in the direction of the magnetic field. We also find a peculiar scaling of the mean velocity, according to which the reciprocal von Karman coefficient grows nearly linearly with the distance to the wall.

Investigation of the laminar viscous flow in a semi-porous channel in the presence of uniform magnetic field using optimal homotopy asymptotic method

Abstract: In this paper, the problem of laminar viscous flow in a semi-porous channel in the presence of transverse magnetic field is studied. The Optimal Homotopy Asymptotic Method (OHAM) is employed to approximate the solution of the system of nonlinear differential equations governing the problem. The influence of the Hartmann number (Ha) and the Reynolds number (Re) on the flow was investigated. The results of the OHAM were compared with homotopy analysis method (HAM) and variation iteration method (VIM) results.

Investigation of Prandtl number effect on natural convection MHD in an open cavity by lattice Boltzmann method

Abstract: Purpose – Magneto hydrodynamic (MHD) flows in fluids is known to have an important effect on heat transfer and fluid flow in various substances while the quality of the substances and the considered shapes can influence the amount of changes. Thus, MHD flows in a different form and widespread alterations in the kind of the material and the power of MHD flow were carried out by lattice Boltzmann method (LBM) in this investigation. The aim of this paper is to identify the ability of LBM for solving MHD flows as the effect of different substances in the presence of the magnetic field changes.Design/methodology/approach – This method was utilized for solving MHD natural convection in an open cavity while Hartmann number varies from 0 to 150 and Rayleigh number is considered at values of Ra=103, 104 and 105, with the Prandtl number altering in a wide range of Pr=0.025, 0.71 and 6.2. An appropriate validation with previous numerical investigations demonstrated that this attitude is a suitable method for MHD pro...

Instabilities and turbulence in magnetohydrodynamic flow in a toroidal duct prior to transition in Hartmann layers

Abstract: Flow of an electrically conducting fluid in a toroidal duct of square cross-section is analysed. The flow is driven by the azimuthal Lorentz force resulting from the interaction between the radial electric currents created by the difference of electric potential maintained between the cylinder walls and the strong magnetic field imposed in the axial direction. The flow geometry and the value of the Hartmann number correspond to the experiment of Moresco & Alboussiere (J. Fluid Mech., vol. 504, 2004, pp. 167–181). The purpose of the analysis is to reveal the flow features at Reynolds numbers below the threshold of transition to turbulence in Hartmann layers. We find that the flow experiences a complex evolution. The laminar base flow experiences the first instability at the Reynolds number significantly smaller than that of the threshold. The instability is axisymmetric and oscillatory. Turbulence appears at a slightly higher Reynolds number. Right up to the Hartmann layer instability, the turbulence remains localized in a layer near the outer cylinder wall. It is demonstrated that the turbulence may affect the transition in the Hartmann layers via unsteady forcing of the outer flow.

Slip Effects on the Unsteady MHD Pulsatile Blood Flow through Porous Medium in an Artery under the Effect of Body Acceleration

Abstract: Unsteady pulsatile flow of blood through porous medium in an artery has been studied under the influence of periodic body acceleration and slip condition in the presence of magnetic field considering blood as an incompressible electrically conducting fluid. An analytical solution of the equation of motion is obtained by applying the Laplace transform. With a view to illustrating the applicability of the mathematical model developed here, the analytic explicit expressions of axial velocity, wall shear stress, and fluid acceleration are given. The slip condition plays an important role in shear skin, spurt, and hysteresis effects. The fluids that exhibit boundary slip have important technological applications such as in polishing valves of artificial heart and internal cavities. The effects of slip condition, magnetic field, porous medium, and body acceleration have been discussed. The obtained results, for different values of parameters into the problem under consideration, show that the flow is appreciably influenced by the presence of Knudsen number of slip condition, permeability parameter of porous medium, Hartmann number of magnetic field, and frequency of periodic body acceleration. The study is useful for evaluating the role of porosity and slip condition when the body is subjected to magnetic resonance imaging (MRI).

Studying the effects of a longitudinal magnetic field and discrete isoflux heat source size on natural convection inside a tilted sinusoidal corrugated enclosure

Abstract: In the present work, the effects of the longitudinal magnetic field and the heat source size on natural convection heat transfer through a tilted sinusoidal corrugated enclosure for different values of enclosure inclination angles are analyzed and solved numerically by using the finite volume technique based on body fitted control volumes with a collected variable arrangement. A constant heat flux source is discretely embedded at the central part of the bottom wall whereas the remaining parts of the bottom wall and the upper wall are assumed adiabatic, and two vertical sinusoidal corrugated walls are maintained at a constant low temperature. The range of the variable parameters considered in the present analysis is as follows: the enclosure inclination angle is varied from 0^o to 135^o, the ratio of the size of the heating element to enclosure width varied from 20 to 80% of enclosure reference length, Hartmann number is varied from 0 to 100, and Rayleigh number varied from 10^3 to 10^6. Liquid gallium with constant Prandtl number (0.02) is used as a working fluid with constant properties except the density. The obtained results indicated that streamlines are affected strongly by the magnetic field especially for small values of inclination angle (@F=0^o) and Rayleigh number (Ra=10^3-10^6). The magnetic field effect decreases with an increase in the enclosure inclination angle (@F>0^o) especially for large values of Rayleigh number. The increase in Hartmann number will cause the temperature lines to become symmetrical in shape for large values of Rayleigh number (Ra=10^5-10^6). The results also explain that the temperature lines are very little affected by the inclination angle especially for small values of (@e=0.4) and (Ra=10^4), but this effect will increase especially for (@e=0.8) and (Ra=10^6). The Nusselt number increases first with an increase in inclination angle (0^[email protected][email protected]@?45^o), then is slightly affected for (45^o<@[email protected]?90^o), and finally decreases for (90^o<@[email protected]?135^o). An empirical correlation is developed by using Nusselt number versus Hartmann and Rayleigh numbers, and enclosure inclination angle. The increase in Hartmann number and the ratio of heating element to enclosure width will decrease the Nusselt number. Furthermore, four mathematical correlations are extracted from the results and presented, which can be used to accurately predict the average Nusselt number in terms of enclosure inclination angle, Hartmann, and Rayleigh numbers.

MHD oblique stagnation-point flow of a Newtonian fluid

Abstract: The steady two-dimensional oblique stagnation-point flow of an electrically conducting Newtonian fluid in the presence of a uniform external electromagnetic field (E0, H0) is analysed, and some physical situations are examined. In particular, if E0 vanishes, H0 lies in the plane of the flow, with a direction not parallel to the boundary, and the induced magnetic field is neglected, it is proved that the oblique stagnation-point flow exists if and only if the external magnetic field is parallel to the dividing streamline. In all cases it is shown that the governing nonlinear partial differential equations admit similarity solutions, and the resulting ordinary differential problems are solved numerically. Finally, the behaviour of the flow near the boundary is analysed; this depends on the Hartmann number if H0 is parallel to the dividing streamline.

Effect of induced magnetic field on natural convection in vertical concentric annuli

Abstract: In the present paper, we have considered the steady fully developed laminar natural convective flow in open ended vertical concentric annuli in the presence of a radial magnetic field. The induced magnetic field produced by the motion of an electrically conducting fluid is taken into account. The transport equations concerned with the considered model are first recast in the non-dimensional form and then unified analytical solutions for the velocity, induced magnetic field and temperature field are obtained for the cases of isothermal and constant heat flux on the inner cylinder of concentric annuli. The effects of the various physical parameters appearing into the model are demonstrated through graphs and tables. It is found that the magnitude of maximum value of the fluid velocity as well as induced magnetic field is greater in the case of isothermal condition compared with the constant heat flux case when the gap between the cylinders is less or equal to 1.70 times the radius of inner cylinder, while reverse trend occurs when the gap between the cylinders is greater than 1.71 times the radius of inner cylinder. These fields are almost the same when the gap between the cylinders is equal to 1.71 times the radius of inner cylinder for both the cases. It is also found that as the Hartmann number increases, there is a flattening tendency for both the velocity and the induced magnetic field. The influence of the induced magnetic field is to increase the velocity profiles.

Reactive solute transfer in magnetohydrodynamic boundary layer stagnation-point flow over a stretching sheet with suction/blowing

Abstract: The article is concerned with the study of reactive solute distribution in the laminar boundary layer stagnation-point flow of an electrically conducting viscous incompressible fluid over a stretching sheet with suction or blowing. The fluid is permeated by a magnetic field produced by an electric current. The self-similar equations for momentum and mass transfer are obtained and solved numerically by finite difference method using quasi-linearization technique. The velocity and reactive concentration profiles for various values of parameters involved in the system are presented through graphs and analyzed physically. They reveal that the momentum and solute boundary layer thicknesses decrease with increasing values of b/a 1. Furthermore, it is noted that with the increase of Hartmann number, the solute transfer increases when b/a 1, but the opposite behavior has been noticed in the case of velocity profiles.

Enhancing heat transfer in a high Hartmann number magnetohydrodynamic channel flow via torsional oscillation of a cylindrical obstacle

Abstract: An approach is studied for side-wall heat transfer enhancement in the magnetohydrodynamic flow of fluid in a rectangular duct that is damped by a strong transverse magnetic field. The mechanism employs the rotational oscillation of a cylinder placed inside the duct to encourage vortex shedding, which promotes the mixing of fluid near a hot duct wall with cooler fluid in the interior. The effectiveness of the heat transfer enhancement is investigated over a wide range of oscillation amplitudes and forcing frequencies. The motivation for exploring this mechanism is inspired by the transient growth response of this flow, which indicates that the optimal disturbances feeding the vortex shedding process are localized near the cylinder, and are characterized by an asymmetrical disturbance with respect to the wake centreline. The results show that a considerable increase in heat transfer from the heated channel wall due to rotational oscillation of the cylinder can be achieved, with the maximum enhancement of mo...

Magnetohydrodynamic peristaltic flow of a couple stress fluid through coaxial channels containing a porous medium

Abstract: This article studies the hydromagnetic peristaltic flow of couple stress fluids through the gap between two concentric channels containing a Darcian porous medium, with the inner channel being rigid. A sinusoidal wave propagates along the outer channel. Long wavelength and low Reynolds number assumptions are used. The effects of couple stress parameter, magnetic field, permeability, and the channel ratio width on pressure and frictional forces on the inner and outer channels are depicted graphically. Mechanical efficiency and trapping are also studied. Pressure diminishes with increasing coupling and permeability parameters whereas it increases with Hartmann number and channel width ratio. Applications of the model include transport of complex bio-waste fluids and magnetic field control of gastro-intestinal disorders.

Heat transfer augmentation of magnetohydrodynamics natural convection in l-shaped cavities utilizing nanofluids

Abstract: A numerical study of natural convection heat transfer through an alumina-water nanofluid inside L-shaped cavities in the presence of an external magnetic field is performed. The study has been carried out for a wide range of important parame­ters such as Rayleigh number, Hartmann number, aspect ratio of the cavity and solid volume fraction of the nanofluid. The influence of the nanoparticle, buoyancy force and the magnetic field on the flow and temperature fields have been plotted and discussed. The results show that after a critical Rayleigh number depending on the aspect ratio, the heat transfer in the cavity rises abruptly due to some significant changes in flow field. It is also found that the heat transfer enhances in the presence of the nanoparticles and increases with solid volume fraction of the nanofluid. In addition, the performance of the nanofluid utilization is more effective at high Ray­leigh numbers. The influence of the magnetic field has been also studied and de­duced that it has a remarkable effect on the heat transfer and flow field in the cavity that as the Hartmann number increases the overall Nusselt number is significantly decreased specially at high Rayleigh numbers.

Analytical solution of mixed electromagnetic/pressure driven gaseous flows in microchannels

Abstract: The influences of wall-slip/jump conditions on the fluid flow and heat transfer for hydrodynamically and thermally fully developed electrically conducting gaseous flow subject to an electromagnetic field inside a parallel plate microchannel with constant heat flux at walls are studied under the assumptions of a low-magnetic Reynolds number. The governing equations are non-dimensionalized and then analytical solutions are derived for the friction and the heat transfer coefficients. The fluid flow and the heat transfer characteristics obtained in the analytical solutions are discussed in detail for different parameters such as the Knudsen, Hartmann, and Brinkman numbers. The velocity profiles verify that even with a constant Knudsen number, applying a stronger electromagnetic field gives rise to an increase in the slip velocity. The results also reveal that on increasing the Hartmann number, the heat transfer rate as well as the friction factor is enhanced, whereas it tends to suppress the movement of the fluid. Further, it is found that the Nusselt and the Poiseuille numbers are less sensitive to the electromagnetic field effects with increase in rarefaction.

Mathematical Analysis of Unsteady MHD Blood Flow through Parallel Plate Channel with Heat Source

Abstract: In the present study, a mathematical model of unsteady blood flow through parallel plate channel under the action of an applied constant transverse magnetic field is proposed. The model is subjected to heat source. Analytical expressions are obtained by choosing the axial velocity; temperature distribution and the normal velocity of the blood depend on y and t only to convert the system of partial differential equations into system of ordinary differential equations under the conditions defined in our model. The model has been analyzed to find the effects of various parameters such as, Hartmann number, heat source parameter and Prandtl number on the axial velocity, temperature distribution and the normal velocity. The numerical solutions of axial velocity, temperature distributions and normal velocity are shown graphically for better understanding of the problem. Hence, the present mathematical model gives a simple form of axial velocity, temperature distribution and normal velocity of the blood flow so that it will help not only people working in the field of Physiological fluid dynamics but also to the medical practitioners.

Effect of the magnetic field on the hydrodynamic permeability of a membrane

Abstract: The present paper concerns the influence of the magnetic field on the permeability of a membrane of solid cylindrical particles covered with porous layer. Here, we have considered the flow along the axis of cylinder and the alignment of uniform magnetic field is assumed to be perpendicular to the axis. The Brinkman equation is used for flow through porous region and Stokes equation is used for flow through clear fluid region. To model flow through assemblage of particles, cell model technique has been used i.e. the porous cylindrical shell is assumed to be confined within a hypothetical cell of same geometry. The stress jump condition has been employed at the fluid-porous interface and all four alternative conditions Happel, Kuwabara, Kvashnin and Mehta-Morse/Cunningham are used at the hypothetical cell. Effect of the Hartmann number on the hydrodynamic permeability of the membrane is discussed.

Lattice Boltzmann simulation of MHD mixed convection in a two-sided lid-driven square cavity

Abstract: In this paper the effects of a magnetic field on mixed convection flow in a two-sided lid-driven cavity have been analyzed by the lattice Boltzmann method (LBM). The Hartmann number varied from Ha = 0 to 100. The study has been conducted for different Richardson numbers (Ri) from 0.01 to 100 while the direction of the magnetic field was investigated in the x-direction. Consequences demonstrate that the heat transfer augments with an increment of the Richardson number for different Hartmann numbers for two cases. The heat transfer declines with the growth of the magnetic field for various Richardson numbers for two cases. The difference between the values of heat transfer for the two cases at variant parameters is negligible but the trend of fluid flow for the two cases is multifarious. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20402

Finite Element Solution of MHD Transient Flow past an Impulsively Started Infinite Horizontal Porous Plate in a Rotating Fluid with Hall Current

Abstract: The problem of a transient three dimensional MHD flow of an electrically conducting viscous incompressible rotating fluid past an impulsively started infinite horizontal porous plate taking into account the Hall current is presented. It is assumed that the fluid rotates with a constant angular velocity about the normal to the plate and a uniform magnetic field applied along the normal to the plate and directed into the fluid region. The magnetic Reynolds number is assumed to be so small that the induced magnetic field can be neglected. The non-dimensional equations governing the flow are solved by Galerkin finite element method. The expressions for the primary and secondary velocity fields are obtained in non-dimensional form. The effects of the physical parameters like M (Hartmann number), Ω (Rotation parameter) and m (Hall parameter) on these fields are discussed through graphs and results are physically interpreted.

Linear stability of magnetohydrodynamic flow in a perfectly conducting rectangular duct

Abstract: We analyse numerically the linear stability of a liquid-metal flow in a rectangular duct with perfectly electrically conducting walls subject to a uniform transverse magnetic field. A non-standard three-dimensional vector stream-function/vorticity formulation is used with a Chebyshev collocation method to solve the eigenvalue problem for small-amplitude perturbations. A relatively weak magnetic field is found to render the flow linearly unstable as two weak jets appear close to the centre of the duct at the Hartmann number In a sufficiently strong magnetic field, the instability following the jets becomes confined in the layers of characteristic thickness located at the walls parallel to the magnetic field. In this case the instability is determined by which results in both the critical Reynolds number and wavenumber scaling as Instability modes can have one of the four different symmetry combinations along and across the magnetic field. The most unstable is a pair of modes with an even distribution of vorticity along the magnetic field. These two modes represent strongly non-uniform vortices aligned with the magnetic field, which rotate either in the same or opposite senses across the magnetic field. The former enhance while the latter weaken one another provided that the magnetic field is not too strong or the walls parallel to the field are not too far apart. In a strong magnetic field, when the vortices at the opposite walls are well separated by the core flow, the critical Reynolds number and wavenumber for both of these instability modes are the same: and The other pair of modes, which differs from the previous one by an odd distribution of vorticity along the magnetic field, is more stable with an approximately four times higher critical Reynolds number.