Taylor Vortex Flow Research Articles

A modified compact numerical algorithm to solve 2D Navier-Stokes equation

In this paper a modified fourth order compact scheme for solving unsteady 2-D Navier-stokes equation in stream function-vorticity formulation is proposed. The proposed scheme involves domain transformation and the governing cartesian equations are transformed to body fitted coordinate system. Explicit Euler’s forward discretization in time and central difference in space are applied except for few nodes adjacent to the computational boundaries. The scheme is tested on two benchmark problems Taylor vortex flow, Burgraff flow. The results in numerical form are compared with exact solutions and are in excellent agreement.

Taylor-vortex flow in shear-thinning fluids.

This paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding of the influence of the viscosity stratification and the nonlinear variation of the effective viscosity μ with the shear rate γ[over ̇] on the flow structure in the Taylor-vortex flow regime. A wide gap configuration (η=0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order, is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns is shifted axially toward the radial outflow boundaries (z=0,z/λ_{z}=1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes stronger than the inflow and the extent of the inflow zone where the vorticity is low increases acoordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.

Statistics, plumes and azimuthally travelling waves in ultimate Taylor–Couette turbulent vortices

In this paper, we experimentally study the influence of large-scale Taylor rolls on the small-scale statistics and the flow organization in fully turbulent Taylor–Couette flow for Reynolds numbers up to $Re_{S}=3\times 10^{5}$. The velocity field in the gap confined by coaxial and independently rotating cylinders at a radius ratio of $\unicode[STIX]{x1D702}=0.714$ is measured using planar particle image velocimetry in horizontal planes at different cylinder heights. Flow regions with and without prominent Taylor vortices are compared. We show that the local angular momentum transport (expressed in terms of a Nusselt number) mainly takes place in the regions of the vortex in- and outflow, where the radial and azimuthal velocity components are highly correlated. The efficient momentum transfer is reflected in intermittent bursts, which becomes visible in the exponential tails of the probability density functions of the local Nusselt number. In addition, by calculating azimuthal energy co-spectra, small-scale plumes are revealed to be the underlying structure of these bursts. These flow features are very similar to the one observed in Rayleigh–Bénard convection, which emphasizes the analogies of these systems. By performing a complex proper orthogonal decomposition, we remarkably detect azimuthally travelling waves superimposed on the turbulent Taylor vortices, not only in the classical but also in the ultimate regime. This very large-scale flow pattern, which is most pronounced at the axial location of the vortex centre, is similar to the well-known wavy Taylor vortex flow, which has comparable wave speeds, but much larger azimuthal wavenumbers.

Suspension Taylor–Couette flow: co-existence of stationary and travelling waves, and the characteristics of Taylor vortices and spirals

Flow visualization and particle image velocimetry (PIV) measurements are used to unravel the pattern transition and velocity field in the Taylor–Couette flow (TCF) of neutrally buoyant non-Brownian spheres immersed in a Newtonian fluid. With increasing Reynolds number ($Re$) or the rotation rate of the inner cylinder, the bifurcation sequence in suspension TCF remains same as in its Newtonian counterpart (i.e. from the circular Couette flow (CCF) to stationary Taylor vortex flow (TVF) and then to travelling wavy Taylor vortices (WTV) with increasing $Re$) for small particle volume fractions ($\unicode[STIX]{x1D719}<0.05$). However, at $\unicode[STIX]{x1D719}\geqslant 0.05$, non-axisymmetric patterns such as (i) the spiral vortex flow (SVF) and (ii) two mixed or co-existing states of stationary (TVF, axisymmetric) and travelling (WTV or SVF, non-axisymmetric) waves, namely (iia) the ‘TVF$+$WTV’ and (iib) the ‘TVF$+$SVF’ states, are found, with the former as a primary bifurcation from CCF. While the SVF state appears both in the ramp-up and ramp-down experiments as in the work of Majji et al. (J. Fluid Mech., vol. 835, 2018, pp. 936–969), new co-existing patterns are found only during the ramp-up protocol. The secondary bifurcation TVF $\leftrightarrow$ WTV is found to be hysteretic or sub-critical for $\unicode[STIX]{x1D719}\geqslant 0.1$. In general, there is a reduction in the value of the critical Reynolds number, i.e. $Re_{c}(\unicode[STIX]{x1D719}\neq 0)<Re_{c}(\unicode[STIX]{x1D719}=0)$, for both primary and secondary transitions. The wave speeds of both travelling waves (WTV and SVF) are approximately half of the rotational velocity of the inner cylinder, with negligible dependence on $\unicode[STIX]{x1D719}$. The analysis of the radial–axial velocity field reveals that the Taylor vortices in a suspension are asymmetric and become increasingly anharmonic, with enhanced radial transport, with increasing particle loading. Instantaneous streamline patterns on the axial–radial plane confirm that the stationary Taylor vortices can indeed co-exist either with axially propagating spiral vortices or azimuthally propagating wavy Taylor vortices – their long-time stability is demonstrated. It is shown that the azimuthal velocity is considerably altered for $\unicode[STIX]{x1D719}\geqslant 0.05$, resembling shear-band type profiles, even in the CCF regime (i.e. at sub-critical Reynolds numbers) of suspension TCF; its possible role on the genesis of observed patterns as well as on the torque scaling is discussed.

Taylor-Couette flow of shear-thinning fluids

The flow between two concentric cylinders, one of which is rotating (Taylor-Couette flow), has been the focus of extensive research, due to the number of flow instabilities that may occur and its use in various industrial applications. We examine Taylor-Couette flow of Newtonian and shear-thinning fluids (solutions of xanthan gum in water/glycerol) using a combination of particle-image velocimetry and flow visualization for a wide range of Reynolds number, spanning the circular Couette flow, Taylor vortex flow, and wavy vortex flow regimes. Shear thinning is associated with an increase in the axial wavelength and has a nonmonotonic effect on the critical Reynolds number for transition to Taylor vortex flow and wavy vortex flow. The magnitude of vorticity and the strength of the radial jets transporting fluid away from the inner cylinder (“outward jets”) are both reduced in shear-thinning fluids relative to the Newtonian case; the vorticity in the shear-thinning fluids also tends to concentrate at the edges of vortices, rather than in the cores. In the wavy vortex flow regime for Newtonian fluids, the amplitudes of the waves at the “inward jets” (moving toward the inner cylinder) are low compared to those at the outward jets. However, for the shear-thinning fluids, the amplitudes of the waves at both the inward and outward jets tend to be significantly larger. Finally, shear thinning is associated with greater variations in time and space: we observe slow drifts in the axial positions of vortices and spatial variations in the amplitudes of the wavy instability, which are absent in Newtonian fluids.

Numerical Analysis of Critical Reynolds Number of Wavy Taylor Vortex Flow with Changing Aspect Ratio

Taylor vortex flow is one of the important vortex flows that have been studied since its classic study made by G. I. Taylor in 1923. State of the flow between inner and outer cylinders of a rotating co-axial cylinder transits from Couette flow to Taylor vortex flow and to wavy Taylor vortex flow as the increase of Reynolds number. This study has identified the critical Reynolds number when the flow changes from Taylor vortex flow to wavy Taylor vortex flow. The numerical analysis making use of the attractor in the chaos theory has been used in this identification of the critical Reynolds number. The calculated critical Reynolds numbers of each flow mode are almost identical to the values obtained by the visualization experiment at small aspect ratios. In the region where the aspect ratio is larger than the ratio at the peak critical Reynolds number, the distribution of the Reynolds number is qualitatively similar between the calculated and experimental values.

Hydrodynamic education with rheoscopic fluid

We present a educational poster supporting the subject „Mechanics of fluids I“, which the students evaluate to be difficult mainly due to abstractness. Our goal is to show in vivo the behavior, especially the non-linearity, of various flows transiting into turbulence. The fluid motion is visualized by using the rheoscopic fluid, which consist of water and the dust of mica, whose particles are longitudinal and shiny resulting into easily observable reflections, when the particles coherently orient along the maximum stress. This happens mainly in shear layers, e.g. at the boundary between vortex core and envelope. An example of flow transiting into turbulence is the Taylor-Couette flow between two concentric cylinders, which with increasing Taylor number passes through various regimes from fully laminar bearing flow through the Taylor vortex flow (TVF) and later Wavy vortex flow (WVF) up to Turbulent Taylor vortices regime (TTV) and, finally, the regime of featureless turbulence.

Families of reversing and non-reversing Taylor vortex flows between two co-oscillating cylinders with different amplitudes

This paper deals with the centrifugal instability of time-modulated Taylor-Couette flow for the case in which the inner and outer cylinders are co-oscillating around zero mean with the angular velocities Ωin = Ω0 cos(ωt) and Ωout = εΩ0 cos(ωt), respectively (Ω0, ω, and ε denote, respectively, the amplitude, the frequency of the modulated rotation, and the amplitudes ratio). The small-gap equations for the stability of this flow with respect to axisymmetric disturbances are derived and solved on the basis of Floquet theory. We recover in the case ε = 0 where the outer cylinder is stationary while the inner is modulated the two well-known reversing and non-reversing Taylor vortex flows. Attention is focused on the evolution of these time-dependent flows when one allows the oscillation of the outer cylinder. It turns out that an increase in the parameter ε leads to the discovery of families of reversing and non-reversing flows and other interesting bifurcation phenomena including codimension-two bifurcation points. In addition, a proper tuning of this parameter ε provides a control of the onset of instability as well as the nature of the primary bifurcation. Moreover, it is shown that when ε > 1, the instability is suppressed in low frequencies and the flow is always stable in good agreement to what is obtained by a quasi-steady approach where transient instability is detected. This latter is attributed to the fluid inertia taking place when the cylinders are reversing their rotation’s direction. However, no effect of the parameter ε is observed in high frequencies where the instability develops in thin boundary Stokes layers near the oscillating cylinders.

Структуры течений во вращающемся цилиндре с жидкостью и свободным цилиндрическим ядром при вибрациях

In the present work, the modes of steady time-average flows are studied experimentally, which are realized in a quasi-coaxial layer at circular inertial oscillations of a free cylindrical core and its simultaneous differential rotation. The outer cylinder is formed by the wall of a hermetically sealed rotating container. The inner cylinder (core) is hollow and made of polyester film. The volume between the cylinders is filled with a low-viscosity incompressible fluid (water), into which small heavy particles are added, which serve for visualization. The container is installed horizontally and rotates rapidly, so that the core occupies a stable position on the cavity axis. To measure the rotation rate of the core, synchronization with the flicker frequency of a stroboscope is used; to study the flow structure by the distribution of visualizer particles, photo-recording is used. To excite the core oscillations, translational vibrations are applied to the container directed perpendicular to the axis of rotation. In this case, an intensive leading rotation of the core is generated. Depending on the mode of the core motion, various distribution structures of the visualizers are observed. At relatively low rates of the core rotation, structures with a spatial period characteristic of inertial waves are observed. In the case of moderate rates, one observes a regular system of toroidal vortices. At high rates, the flow becomes irregular. The system of toroidal vortices is associated with the centrifugal instability. The threshold of its occurrence is noticeably lower than in the case of the classical Couette–Taylor flow. Analysis of the results shows that the system under study has essential prerequisites for the lowering of the onset threshold of Taylor vortex flow.

Self-sustaining process in Taylor-Couette flow

The transition from Tayor vortex flow to wavy-vortex flow is revisited. The Self-Sustaining Process (SSP) of Waleffe [Phys. Fluids 9, 883-900 (1997)] proposes that a key ingredient in transition to turbulence in wall-bounded shear flows is a three-step process involving rolls advecting streamwise velocity, leading to streaks which become unstable to a wavy perturbation whose nonlinear interaction with itself feeds the rolls. We investigate this process in Taylor-Couette flow. The instability of Taylor-vortex flow to wavy-vortex flow, a process which is the inspiration for the second phase of the SSP, is shown to be caused by the streaks, with the rolls playing a negligible role, as predicted by Jones [J. Fluid Mech. 157, 135-162 (1985)] and demonstrated by Martinand et al. [Phys. Fluids 26, 094102 (2014)]. In the third phase of the SSP, the nonlinear interaction of the waves with themselves reinforces the rolls. We show this both quantitatively and qualitatively, identifying physical regions in which this reinforcement is strongest, and also demonstrate that this nonlinear interaction depletes the streaks.

Continuous Synthesis of Structurally Uniform Graphene Oxide Materials in a Model Taylor–Couette Flow Reactor

Graphene oxide (GO) has proven to be an invaluable material for a wide range of applications. The development of a bulk-scale continuous process to synthesize GO materials has become crucial. In this study, we used a model Taylor–Couette reactor with axial flow to transform the oxidation of graphite flakes into a continuous process. Efficient mixing of graphite and oxidizing agents was achieved via Taylor vortices, which remarkably shortened the duration of graphite oxide (GtO) synthesis from hours to minutes. Our results reveal that the level of oxidation increased at the Taylor vortex flow (TVF) regime and significantly decreased at other hydrodynamic flow regimes. More importantly, TVF regime resulted in structurally uniform GtO products. This confirms that the developed apparatus offers a robust method to synthesize high-quality, structurally uniform GtO in a continuous manner that can be used in numerous applications.

Numerical investigation of the effect of different working fluids on the pattern formation in a narrow rotating annulus

Fluid evolving in an annular gap between two coaxial cylinders, well known as Taylor–Couette flow, is one of the fundamental problems in fluid mechanics for the study of instabilities and the transition to turbulence. This flow system is typically a closed environment, where the working fluid is confined axially by end-plates and radially between the cylinders. In this work, we investigate, via CFD simulation, the influence of the working fluids confined inside an infinite aspect ratio Taylor–Couette system on the onset of cellular pattern. The inner cylinder rotates freely about a vertical axis through its centre, while the outer one, the upper and bottom end-caps are held at rest. The basic system is characterized by a height H = 150 mm, an annular gap d = 5 mm, a ratio of the inner to the outer cylinders radii η = 0.909, an aspect ratio corresponding to the cylinders height reported to the gap length Γ = 30 and a ratio of the gap to the radius of the inner cylinder δ = 0.1. The flow behaviour and the time-independent formation of axisymmetric vortices are investigated under steady-state condition. The main goal of this work is to show how the change in cellular pattern operates when changing the working fluid by simulating and comparing four different liquids, namely hydrogen, helium, lithium and water. Particular attention is given to the onset of Taylor vortices in the vicinity of the threshold of transition, i.e. from the laminar Couette flow to the occurrence of Taylor vortex flow. In addition, the flow patterns are presented in terms of distributions of wall shear stress, skin friction coefficient, streamlines and velocity components. The computed results show that the critical Taylor number for the different liquids is the same, Tac1 = 42.4. Interestingly, lithium and hydrogen exhibit quite different behaviours than other liquids. The shape and wavelength of Ekman cells and the Taylor vortices for lithium and hydrogen show significant changes compared to water and helium.

Heat transfer characteristics of Taylor vortex flow with shear-thinning fluids

This study numerically investigates the heat transfer characteristics, including the fluid flow, of a Taylor vortex flow system with shear-thinning fluids. Governing equations were solved using OpenFOAM® 4.0 code. The Carreau model was utilized as the rheological model. The parameter (n) in the Carreau model, which describes the slope of a decrease in viscosity with an increase in shear-rate, was varied from 1 to 0.3. The local Nusselt number (NuL) decreased with the increase in shear-thinning property. Furthermore, a correlation equation between the effective Reynolds number (Reeff) and a global Nusselt number (NuG) was proposed. Using this equation, NuG was evaluated within a ± 10% error in the case of n = 1, 0.7, 0.5, and within a ± 20% error in the case of n = 0.3. The size of the Taylor vortices became axially larger with an increase in the shear-thinning property. Furthermore, the thickness of the boundary layer of velocity and temperature increased with an increase in shear-thinning property. The ratio of the thickness of velocity boundary layer to the temperature boundary layer monotonically decreased with an increase in Reeff.

The cavitating Taylor-Couette flow

This work presents an investigation of a new phenomenon of the Taylor-Couette flow: the onset of Taylor vortices in a cavitating fluid. This particular form of the Taylor-Couette flow develops if the shear flow between a rotating inner and a fixed outer cylinder approaches the critical Taylor number and the vapor pressure of the fluid simultaneously. This process is achieved by increasing the rotational speed of the inner cylinder, which causes an increase of the radial pressure gradient inside the laminar flow. The fully developed Taylor vortex flow is characterized by a pressure distribution in the azimuthal plane showing a local minimum adjacent to the wall of the inner cylinder between a pair of vortices that form a radial flow towards the outer cylinder. Thence, cavitation occurs simultaneously if the local pressure minimum drops below the vapor pressure of the fluid. This transition from a two-dimensional (Couette) into a three-dimensional (Taylor) flow triggered the idea to apply a newly developed unsteady 2-phase 3D-computational fluid dynamics code by computing the generation of vapor that is coinciding with the formation of Taylor vortices at the critical Taylor number. Whereas the results of a numerical simulation prove the existence of toroidal vapor caused by cavitation, the experimental validation demands additionally the development of a special fluid. Thus, the present work describes this specifically tailored fluid, which not only fulfills Taylor and pressure analogy but also features a favorable refractive index and a chemical suitability for the task.

Axial mixing and vortex stability to in situ radial injection in Taylor–Couette laminar and turbulent flows

Taylor–Couette flows have been widely studied in part due to the enhanced mixing performance from the variety of hydrodynamic flow states accessible. These process improvements have been demonstrated despite the traditionally limited injection mechanisms from the complexity of the Taylor–Couette geometry. In this study, using a newly designed, modified Taylor–Couette cell, axial mass transport behaviour is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the measured dispersion coefficient was found to increase with increasing $Re$, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A dimensionless stability criterion, the ratio of injection to diffusion time scales, was found to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, $Re$.

Interaction dynamics of longitudinal corrugations in Taylor-Couette flows

In this paper, numerical simulations are performed on the interaction of vortices with a longitudinal corrugated wall in a Taylor-Couette (TC) setting with the inner smooth surface cylinder rotating and the outer corrugated surface cylinder stationary. The motivation of the study is to shed light on how such an interaction affects the drag/torque with respect to two geometric parameters of the corrugations, namely, the wavelength λc* and amplitude A*, where * indicates a normalization by the gap width d. Results show that in the circular Couette flow regime, the secondary vortices induced by the corrugations cause the torque to increase. When λc*<1, there is a linear relationship between torque and λc*, and when λc*>1, there is a steeper increase of torque due to the interaction of the growing secondary vortices and the opposite wall. In the Taylor-vortex flow regime, the interaction between the Taylor vortices and the corrugations produces three distinct behaviors characterized by λc*. As the wavelength increases, our results show that the stronger modulation effects can override the inherent TC flow dynamics, which in turn leads to a wide range of flow structures that can have a significant impact on the resulting drag/torque characteristics. Generally, a torque reduction is achieved when λc*≤1, while forcing the Taylor vortices to stay on the crests of the corrugations can lead to significant improvement in torque reduction. Finally, the geometrical shape of the corrugations mainly alters the wall shear stress distribution on the corrugated wall, with a negligible effect on the flow dynamics when compared to λc*.

Linear stability analysis of the flow between rotating cylinders of wide gap

This study investigated by an analytical method the flow that develops in the gap between concentric rotating cylinders when the Taylor number Ta exceeds the first critical value. Concentric cylinders rotating at the speed ratio μ=0 are investigated over the radius ratio range 0.20≤η≤0.95. This range includes configurations characterised by a larger annular gap width d than classical journal bearing test cases and by a Taylor number beyond the first critical Taylor number at which Taylor vortices develop. The analysis focuses on determining the parameters for the direct transition from axisymmetric Couette flow to wavy Taylor vortex flow. The results show a marked change in trend as the radius ratio η reduces below 0.49 and 0.63 for the azimuthal wave-numbers m=2 and 3 respectively. The axial wavenumber increases so that the resulting wavy Taylor vortex flow is characterised by vortex structures elongated in the radial direction, with a meridional cross-section that is significantly elliptical. The linear stability analysis of the perturbation equations suggests this instability pattern is neutrally stable. Whereas a direct transition from axisymmetric Couette flow is not necessarily the only route for the onset of wavy Taylor vortex flow, the significant difference between the predicted pattern at large gap widths and classical wavy Taylor vortex flow merits further investigation.

DNS of Taylor–Couette flow between counter-rotating cylinders at small radius ratio

A counter-rotating Taylor-Couette flow with relatively small radius ratios of $\eta$ = 0.2--0.5 was investigated over a wide range of the Reynolds number, from laminar to turbulent regime, by means of three-dimensional direct numerical simulations. We investigated the $\eta$ dependence of the flow structure and determined a critical value between $\eta$ = 0.2 and 0.3, below which, the stable outer cylinder side exhibited a modal structure that was different from the Taylor-vortex flow on the inner side. At $\eta \geq$ 0.3, the Taylor-vortex on the unstable inner side dominated the entire flow field between the cylinders, whose footprints were observed in the vicinity of the outer cylinder wall. However, for $\eta$ = 0.2, the influence from the inner side was limited up to the centre of the cylinder gap. Moreover, on the stable outer cylinder side, there appeared a modal structure that was axially homogeneous, azimuthally periodic, and similar to the Tollmien-Schlichting (TS) instability wave. As the Reynolds number increased with a fixed $\eta$ = 0.2, the modal structure changed its azimuthal wavenumber and thickened radially in the wall unit. Although the Reynolds shear stress on the outer side remained approximately zero, the intensity of the velocity fluctuations was comparable to the Taylor-vortex flows in the central part.

Inertial migration of particles in Taylor-Couette flows

An experimental study of inertial migration of neutrally buoyant particles in the circular Couette flow (CCF), Taylor vortex flow (TVF) and wavy vortex flow (WVF) is reported. This work considers a concentric cylinder Taylor-Couette device with a stationary outer cylinder and rotating inner cylinder. The device has a radius ratio of η = ri/ro = 0.877, where ri and ro are the inner and outer radii of the flow annulus. The ratio of the annular width between the cylinders (δ = ro − ri) and the particle diameter (dp) is α = δ/dp = 20. For η = 0.877, the flow of a Newtonian fluid undergoes transitions from CCF to TVF and TVF to WVF at Reynolds numbers Re = 120 and 151, respectively, and for the dilute suspensions studied here, these critical Reynolds numbers are almost unchanged. In CCF, particles were observed to migrate, due to the competition between the shear gradient of the flow and the wall interactions, to an equilibrium location near the middle of the annulus with an offset toward the inner cylinder. In TVF, the vortex motion causes the particles to be exposed to the shear gradient and wall interactions in a different manner, resulting in a circular equilibrium region in each vortex. The radius of this circular region grows with increase in Re. In WVF, the azimuthal waviness results in fairly well-distributed particles across the annulus.

Thermomagnetic effects on the stability of Taylor-Couette flow of a ferrofluid in the presence of azimuthal magnetic field

A stability analysis is conducted for the non-isothermal Taylor-Couette flow of a non-conductive ferrofluid under the action of an azimuthal magnetic field. The transition from steady flow to Taylor vortex flow is investigated in terms of the critical Taylor number and with respect to the changes in the magnetic field strength, radial temperature gradient, gap ratio, ferroparticle concentration and size. For the linear stability analysis, infinitesimal perturbations to the velocity, temperature and magnetization fields are considered and the resulting linear system of stability equations is solved using Chebyshev collocation method. Also, the original nonlinear system of equations is solved numerically using a finite element analysis software, and the results are compared with the linear stability analysis results. A significant stabilization is observed under strong magnetic fields for all cases. It is also observed that radial temperature difference has a destabilizing effect on the flow and this effect is amplified when the magnetic field strength is increased. Higher ferroparticle volume fraction and size lead to a strong degree of magnetization of the fluid and amplifies the stabilizing effect of magnetic fields. The stabilization under azimuthal magnetic forces is observed to be smaller for the narrow gap case compared to the wide gap case.