The instability of a layer of fluid heated below and subject to Coriolis forces

1953 ◽  
Vol 217 (1130) ◽  
pp. 306-327 ◽  
Keyword(s):  
Coriolis Force ◽  
Thermal Instability ◽  
Horizontal Layer ◽  
Onset Of Convection ◽  
Dimensional Parameter ◽  
Coriolis Forces ◽  
Effective Gravity ◽  
The Stability ◽  
Bounding Surfaces ◽  
Rayleigh Numbers

This paper is devoted to examining the stability of a horizontal layer of fluid heated below, subject to an effective gravity ( g ) acting (approximately) in the direction of the vertical and the Coriolis force resulting from a rotation of angular velocity Ω about a direction making an angle ϑ with the vertical. It is shown that the effect of the Coriolis force is to inhibit the onset of convection, the extent of the inhibition depending on the value of the non-dimensional parameter T = 4 d 4 Ω 2 cos 2 ϑ/ v 2 , where d denotes the depth of the layer and v is the kinematic viscosity. Tables of the critical Rayleigh numbers ( R c ) for the onset of convection are provided for the three cases ( a ) both bounding surfaces free, ( b ) both bounding surfaces rigid and ( c ) one bounding surface free and the other rigid. In all three cases R c →constant x T 2/3 as T →∞ ; the corresponding dependence of the critical temperature gradient (— β c ) for the onset of convection, on v and d , is gαβ c = constant x ĸ (Ω 4 cos 4 ϑ/ d 4 v ) 1/2 ( ĸ is the coefficient of thermometric conductivity and α is the coefficient of volume expansion). The question whether thermal instability can set in as oscillations of increasing amplitude (i.e. as 'overstability’) is examined for case ( a ), and it is shown that if ĸ/v <1.478, this possibility does not arise; but if ĸ/v >1.478, over-stability is the first type of instability to arise for all T greater than a certain determinate value. It further appears that these latter possibilities should be considered in meteorological and astrophysical applications of the theory.

The stability of viscous flow between rotating cylinders in the presence of a magnetic field

1953 ◽  
Vol 216 (1126) ◽  
pp. 293-309 ◽  
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Viscous Flow ◽  
Thermal Instability ◽  
Horizontal Layer ◽  
Rotational Stability ◽  
Marginal Stability ◽  
Inhibiting Effect ◽  
The Stability ◽  
The Magnetic Field

In this paper the theory of the stability of viscous flow between two rotating coaxial cylinders which has been developed by Taylor, Jeffreys and Meksyn is extended to the case when the fluid considered is an electrical conductor and a magnetic field along the axis of the cylinders is present. A differential equation of order eight is derived which governs the situation in marginal stability; and a significant set of boundary conditions for the problem is formulated. The case when the two cylinders are rotating in the same direction and the difference ( d ) in their radii is small compared to their mean (R 0 ) is investigated in detail. A variational procedure for solving the underlying characteristic value problem and determining the critical Taylor numbers for the onset of instability is described. As in the case of thermal instability of a horizontal layer of fluid heated below, the effect of the magnetic field is to inhibit the onset of instability, the inhibiting effect being the greater, the greater the strength of the field and the value of the electrical conductivity. In both cases, the inhibiting effect of the magnetic field depends on the strength of the field ( H ), the density ( ρ ) and the coefficients of electrical conductivity ( σ ), kinematic viscosity ( v ) and magnetic permeability ( μ ) through the same non-dimensional combination Q =μ 2 H 2 d 2 σ/ pv ; however, the effect on rotational stability is more pronounced than on thermal instability. A table of the critical Taylor numbers for various values of Q is provided.

On the analogy between thermal and rotational hydrodynamic stability

1966 ◽  
Vol 24 (1) ◽  
pp. 165-176 ◽  
Author(s):  
Walter R. Debler
Keyword(s):  
Temperature Distribution ◽  
Initial Temperature ◽  
Rotating Cylinder ◽  
Temperature Profiles ◽  
Convection Pattern ◽  
Onset Of Convection ◽  
Single Vortex ◽  
Angular Velocities ◽  
The Stability ◽  
Rayleigh Numbers

The correspondence between the eigenvalues for the problem of the onset of convection in a fluid confined between two horizontal plates and for the stability of viscous flow between two cylinders rotating at almost the same angular velocity has been known for some time. The recent work of Chandrasekhar (1961) has prompted the extension of the analogy to a larger group of rotating cylinder problems and their associated convection cases in which the primary temperature distribution is parabolic. This paper shows the analogy between these two problems and presents data which give the corresponding temperature distribution for a given ratio of angular velocities between the two cylinders. The equivalent Rayleigh numbers are listed for the Taylor numbers given by Chandrasekhar (1954). The eigenfunctions for several of the parabolic temperature profiles are determined. These results show that the single vortex convection pattern becomes a double vortex for certain initial temperature distributions. The critical Rayleigh numbers for the stability of a layer of water which is near 4 °C is also found by analogy.

scholarly journals Rayleigh-Bénard convection in an elastico-viscous Walters’ (model B’) nanofluid layer

2015 ◽  
Vol 63 (1) ◽  
pp. 235-244 ◽  
Author(s):  
G.C. Rana ◽  
R. Chand
Keyword(s):  
Fluid Model ◽  
Normal Mode Analysis ◽  
Sufficient Conditions ◽  
Lewis Number ◽  
Horizontal Layer ◽  
Linear Stability Theory ◽  
Mode Analysis ◽  
Physical Parameters ◽  
Onset Of Convection ◽  
The Stability

Abstract In this study, the onset of convection in an elastico-viscous Walters’ (model B’) nanofluid horizontal layer heated from below is considered. The Walters’ (model B’) fluid model is employed to describe the rheological behavior of the nanofluid. By applying the linear stability theory and a normal mode analysis method, the dispersion relation has been derived. For the case of stationary convection, it is observed that the Walters’ (model B’) elastico-viscous nanofluid behaves like an ordinary Newtonian nanofluid. The effects of the various physical parameters of the system, namely, the concentration Rayleigh number, Prandtl number, capacity ratio, Lewis number and kinematics visco-elasticity coefficient on the stability of the system has been numerically investigated. In addition, sufficient conditions for the non-existence of oscillatory convection are also derived.

scholarly journals Hall Effect on Bénard Convection of Compressible Viscoelastic Fluid through Porous Medium

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Mahinder Singh ◽  
Chander Bhan Mehta
Keyword(s):  
Magnetic Field ◽  
Porous Medium ◽  
Thermal Instability ◽  
Linear Stability Theory ◽  
Stationary Convection ◽  
Onset Of Convection ◽  
Medium Permeability ◽  
Rayleigh Numbers ◽  
The Magnetic Field ◽  
Mode Technique

An investigation made on the effect of Hall currents on thermal instability of a compressible Walter’s B′ elasticoviscous fluid through porous medium is considered. The analysis is carried out within the framework of linear stability theory and normal mode technique. For the case of stationary convection, Hall currents and compressibility have postponed the onset of convection through porous medium. Moreover, medium permeability hasten postpone the onset of convection, and magnetic field has duel character on the onset of convection. The critical Rayleigh numbers and the wave numbers of the associated disturbances for the onset of instability as stationary convection have been obtained and the behavior of various parameters on critical thermal Rayleigh numbers has been depicted graphically. The magnetic field, Hall currents found to introduce oscillatory modes, in the absence of these effects the principle of exchange of stabilities is valid.

The instability of a layer of fluid heated below and subject to the simultaneous action of a magnetic field and rotation

1954 ◽  
Vol 225 (1161) ◽  
pp. 173-184 ◽  
Keyword(s):  
Magnetic Field ◽  
Kinematic Viscosity ◽  
Critical Rayleigh Number ◽  
Horizontal Layer ◽  
Simultaneous Action ◽  
Free Boundaries ◽  
Complex Behaviour ◽  
Effective Gravity ◽  
Dimensional Parameters ◽  
The Stability

This paper is devoted to an examination of the stability of a horizontal layer of fluid heated below, subject to an effective gravity g acting (approximately) in the direction of the vertical, a magnetic field H and the Coriolis acceleration resulting from a rotation Ω. When g, H and Ω are parallel, the critical Rayleigh number ( R c ) at which convection sets in depends on H and Ω through the non-dimensional parameters Q = μ 2 H 2 d 2 σ/ρv and T = 4Ω 2 d 4 / v 2 where μ, σ and v are the coefficients of magnetic permeability, electrical conductivity and kinematic viscosity, respectively, and d is the depth of the layer considered. In the case when the liquid is confined between two free boundaries the dependence of R c on Q and T is explicitly established. The results reveal some very unexpected features and illustrate the complex behaviour of a fluid under the simultaneous action of a magnetic field and rotation.

scholarly journals Thermosolutal Natural Convection in Partially Porous Domains

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Dominique Gobin ◽  
Benoît Goyeau
Keyword(s):  
Mass Transfer ◽  
Porous Medium ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Fluid Layer ◽  
Horizontal Layer ◽  
Clear Fluid ◽  
Onset Of Convection ◽  
The Stability ◽  
Double Diffusive

In many industrial processes or natural phenomena, coupled heat and mass transfer and fluid flow take place in configurations combining a clear fluid and a porous medium. Since the pioneering work by Beavers and Joseph (1967), the modeling of such systems has been a controversial issue, essentially due to the description of the interface between the fluid and the porous domains. The validity of the so-called one-domain approach—more intuitive and numerically simpler to implement—compared to a two-domain description where the interface is explicitly accounted for, is now clearly assessed. This paper reports recent developments and the current state of the art on this topic, concerning the numerical simulation of such flows as well as the stability studies. The continuity of the conservation equations between a fluid and a porous medium are examined and the conditions for a correct handling of the discontinuity of the macroscopic properties are analyzed. A particular class of problems dealing with thermal and double diffusive natural convection mechanisms in partially porous enclosures is presented, and it is shown that this configuration exhibits specific features in terms of the heat and mass transfer characteristics, depending on the properties of the porous domain. Concerning the stability analysis in a horizontal layer where a fluid layer lies on top of a porous medium, it is shown that the onset of convection is strongly influenced by the presence of the porous medium. The case of double diffusive convection is presented in detail.

scholarly journals Effect of Rotational Modulation on Rayleigh – B´enard Convection in a Couple Stress Liquid

2020 ◽  
Vol 18 (3) ◽  
pp. 1-12
Author(s):  
S Pranesh ◽  
Sangeetha George K
Keyword(s):  
Rayleigh Number ◽  
Couple Stress ◽  
Horizontal Layer ◽  
External Control ◽  
Regular Perturbation ◽  
Onset Of Convection ◽  
Rotational Modulation ◽  
Steady Rotation ◽  
The Stability ◽  
Internal Convection

The Rayleigh-B´enard convection in a couple stress liquid with rotational modulation is studied using the linear analysis based on normal mode technique. The stability of a horizontal layer of fluid heated from below is examined when, in addition to a steady rotation, a time-periodic sinusoidal perturbation is applied. The expression for Rayleigh number and correction Rayleigh number are obtained using regular perturbation method. The expression for correction Rayleigh number is obtained as a function of frequency of modulation, Taylor number, Couple Stress parameter and Prandtl number. It is observed that rotational modulation leads to delay in onset of convection. Rotation modulation is an example of external control of internal convection.

Magneto Thermal Convection in a Compressible Couple-Stress Fluid

2010 ◽  
Vol 65 (3) ◽  
pp. 215-220 ◽  
Author(s):  
Mahinder Singh ◽  
Pardeep Kumar
Keyword(s):  
Magnetic Field ◽  
Couple Stress ◽  
Thermal Instability ◽  
Normal Mode Analysis ◽  
Mode Analysis ◽  
Onset Of Convection ◽  
Electrically Conducting ◽  
Linearized Stability ◽  
The Stability ◽  
The Magnetic Field

The problem of thermal instability of compressible, electrically conducting couple-stress fluids in the presence of a uniform magnetic field is considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For stationary convection, the compressibility, couple-stress, and magnetic field postpone the onset of convection. Graphs have been plotted by giving numerical values of the parameters to depict the stability characteristics. The principle of exchange of stabilities is found to be satisfied. The magnetic field introduces oscillatory modes in the system that were non-existent in its absence. The case of overstability is also studied wherein a sufficient condition for the non-existence of overstability is obtained.

scholarly journals Effect of modulation on the onset of thermal convection

1969 ◽  
Vol 35 (2) ◽  
pp. 243-254 ◽  
Author(s):  
Giulio Venezian
Keyword(s):  
Temperature Field ◽  
Applied Field ◽  
Critical Rayleigh Number ◽  
Perturbation Expansion ◽  
Horizontal Layer ◽  
Time Dependent ◽  
Steady Temperature ◽  
Onset Of Convection ◽  
Time Modulation ◽  
The Stability

The stability of a horizontal layer of fluid heated from below is examined when, in addition to a steady temperature difference between the walls of the layer, a time-dependent sinusoidal perturbation is applied to the wall temperatures. Only infinitesimal disturbances are considered. The effects of the oscillating temperature field are treated by a perturbation expansion in powers of the amplitude of the applied field. The shift in the critical Rayleigh number is calculated as a function of frequency, and it is found that it is possible to advance or delay the onset of convection by time modulation of the wall temperatures.

scholarly journals Thermal convection of dusty compressible Rivlin-Ericksen viscoelastic fluid with hall currents

2012 ◽  
Vol 16 (1) ◽  
pp. 177-192 ◽  
Author(s):  
Urvashi Gupta ◽  
Parul Aggarwal ◽  
Kumar Wanchoo
Keyword(s):  
Magnetic Field ◽  
Thermal Instability ◽  
Normal Modes ◽  
Suspended Particles ◽  
Stationary Convection ◽  
Viscoelastic Parameter ◽  
Electrically Conducting ◽  
Stabilizing Effect ◽  
The Stability ◽  
Rayleigh Numbers

An investigation is made on the effect of Hall currents and suspended particles on the hydromagnetic stability of a compressible, electrically conducting Rivlin-Ericksen elastico-viscous fluid. The perturbation equations are analyzed in terms of normal modes after linearizing the relevant set of hydromagnetic equations. A dispersion relation governing the effects of viscoelasticity, magnetic field, Hall currents, compressibility and suspended particles is derived. For the stationary convection Rivlin-Ericksen fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. Compressibility and magnetic field are found to have a stabilizing effect on the system whereas Hall currents and suspended particles hasten the onset of thermal instability. These analytic results are confirmed numerically and the effects of various parameters on the stability parameter are depicted graphically. The critical Rayleigh numbers and the wavenumbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behavior of various parameters on critical thermal Rayleigh numbers has been depicted graphically. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, suspended particles and Hall currents which were not existing in the absence of these parameters.

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