scholarly journals Finite-amplitude convection in rotating spherical fluid shells

1997 ◽  
Vol 332 ◽  
pp. 359-376 ◽  
Author(s):  
A. Tilgner ◽  
F. H. Busse
Keyword(s):  
Heat Transport ◽  
Critical Value ◽  
Finite Amplitude ◽  
Time Dependent ◽  
Polar Regions ◽  
Onset Of Convection ◽  
Prandtl Numbers ◽  
Spherical Fluid ◽  
Rayleigh Numbers

Finite-amplitude convection in rotating spherical fluid shells is considered for a variety of Prandtl numbers P and Rayleigh numbers Ra up to about 10 times the critical value. Convection at low Rayleigh numbers in the form of azimuthally periodic or weakly aperiodic drifting waves is characterized by relatively low heat transport, especially for P ≲ 1. The transition to strongly time-dependent convection leads to a rapid increase of the heat transport with increasing Rayleigh numbers. Onset of convection in the polar regions is delayed, but contributes a disproportionate fraction of the heat transport at high Rayleigh number. The differential rotation generated by convection, the distributions of helicity, and the role of asymmetry with respect to the equatorial plane are also studied.

Heat transport by parallel-roll convection in a rectangular container

1987 ◽  
Vol 185 ◽  
pp. 205-234 ◽  
Author(s):  
R. W. Walden ◽  
Paul Kolodner ◽  
A. Passner ◽  
C. M. Surko
Keyword(s):  
Rayleigh Number ◽  
Heat Transport ◽  
Critical Rayleigh Number ◽  
Equation Model ◽  
Onset Of Convection ◽  
Infinite Layer ◽  
Lateral Extent ◽  
Prandtl Numbers ◽  
Rayleigh Numbers ◽  
Good Agreement

Heat-transport measurements are reported for thermal convection in a rectangular box of aspect’ ratio 10 x 5. Results are presented for Rayleigh numbers up to 35Rc, Prandtl numbers between 2 and 20, and wavenumbers between 0.6 and 1.0kc, where Rc and kc are the critical Rayleigh number and wavenumber for the onset of convection in a layer of infinite lateral extent. The measurements are in good agreement with a phenomenological model which combines the calculations of Nusselt number, as a function of Rayleigh number and roll wavenumber for two-dimensional convection in an infinite layer, with a nonlinear amplitude-equation model developed to account for sidewell attenuation. The appearance of bimodal convection increases the heat transport above that expected for simple parallel-roll convection.

Low-Prandtl-number convection in a layer heated from below

1981 ◽  
Vol 102 ◽  
pp. 61-74 ◽  
Author(s):  
R. M. Clever ◽  
F. H. Busse
Keyword(s):  
Prandtl Number ◽  
Heat Transport ◽  
Convective Heat ◽  
Critical Value ◽  
Horizontal Layer ◽  
Convection Flow ◽  
Prandtl Numbers ◽  
Steady Solutions ◽  
Rayleigh Numbers ◽  
Horizontal Wavelength

Steady solutions in the form of two-dimensional rolls are obtained numerically for convection in a horizontal layer of a low-Prandtl-number fluid heated from below. Prandtl numbers in the range 0·001 [les ] P [les ] 0·71 are investigated for Rayleigh numbers between the critical value, R = 1708, and R = 20,000 in the case of rigid boundaries. The calculations reveal that the convective heat transport is relatively independent of the Prandtl number at Rayleigh numbers greater than a finite critical value R2 of the order of 5 × 103. At R = 10,000 the convective heat transport varies by only about 30% for Prandtl numbers in the range investigated. As the Rayleigh number is increased above the critical value R2, the streamlines of the convection flow become circular, independent of the horizontal wavelength as long as the latter is larger than or about equal to twice the height of the layer.

scholarly journals Unsteady Finite Amplitude Convection of Water–Copper Nanoliquid in High-Porosity Enclosures

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
P. G. Siddheshwar ◽  
K. M. Lakshmi
Keyword(s):  
Porous Medium ◽  
Heat Transport ◽  
Heat Storage ◽  
Finite Amplitude ◽  
High Porosity ◽  
Two Phase ◽  
Onset Of Convection ◽  
Maximum Heat ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

Unicellular Rayleigh–Bénard convection of water–copper nanoliquid confined in a high-porosity enclosure is studied analytically. The modified-Buongiorno–Brinkman two-phase model is used for nanoliquid description to include the effects of Brownian motion, thermophoresis, porous medium friction, and thermophysical properties. Free–free and rigid–rigid boundaries are considered for investigation of onset of convection and heat transport. Boundary effects on onset of convection are shown to be classical in nature. Stability boundaries in the R1*–R2 plane are drawn to specify the regions in which various instabilities appear. Specifically, subcritical instabilities' region of appearance is highlighted. Square, shallow, and tall porous enclosures are considered for study, and it is found that the maximum heat transport occurs in the case of a tall enclosure and minimum in the case of a shallow enclosure. The analysis also reveals that the addition of a dilute concentration of nanoparticles in a liquid-saturated porous enclosure advances onset and thereby enhances the heat transport irrespective of the type of boundaries. The presence of porous medium serves the purpose of heat storage in the system because of its low thermal conductivity.

Finite amplitude cellular convection

1958 ◽  
Vol 4 (3) ◽  
pp. 225-260 ◽  
Author(s):  
W. V. R. Malkus ◽  
G. Veronis
Keyword(s):  
Rayleigh Number ◽  
Prandtl Number ◽  
Heat Transport ◽  
Stability Problem ◽  
Dominant Role ◽  
Linear Equations ◽  
Finite Amplitude ◽  
Set Up ◽  
Rayleigh Numbers ◽  
Linear Stability Problem

When a layer of fluid is heated uniformly from below and cooled from above, a cellular regime of steady convection is set up at values of the Rayleigh number exceeding a critical value. A method is presented here to determine the form and amplitude of this convection. The non-linear equations describing the fields of motion and temperature are expanded in a sequence of inhomogeneous linear equations dependent upon the solutions of the linear stability problem. We find that there are an infinite number of steady-state finite amplitude solutions (having different horizontal plan-forms) which formally satisfy these equations. A criterion for ‘relative stability’ is deduced which selects as the realized solution that one which has the maximum mean-square temperature gradient. Particular conclusions are that for a large Prandtl number the amplitude of the convection is determined primarily by the distortion of the distribution of mean temperature and only secondarily by the self-distortion of the disturbance, and that when the Prandtl number is less than unity self-distortion plays the dominant role in amplitude determination. The initial heat transport due to convection depends linearly on the Rayleigh number; the heat transport at higher Rayleigh numbers departs only slightly from this linear dependence. Square horizontal plan-forms are preferred to hexagonal plan-forms in ordinary fluids with symmetric boundary conditions. The proposed finite amplitude method is applicable to any model of shear flow or convection with a soluble stability problem.

Convection in a rotating cylindrical annulus. Part 4. Modulations and transition to chaos at low Prandtl numbers

1997 ◽  
Vol 350 ◽  
pp. 209-229 ◽  
Author(s):  
J. HERRMANN ◽  
F. H. BUSSE
Keyword(s):  
Rossby Waves ◽  
Landau Equation ◽  
Neutral Curve ◽  
Onset Of Convection ◽  
Ginzburg Landau ◽  
Cylindrical Annulus ◽  
Chaotic Convection ◽  
Finite Distance ◽  
Prandtl Numbers ◽  
Rayleigh Numbers

Thermal Rossby waves driven by centrifugal buoyancy in a rotating cylindrical fluid gap become unstable right at the onset of convection when the Prandtl number is small. The Benjamin–Feir–Newell instability leads to modulated thermal Rossby waves which can also be described by a generalized Ginzburg–Landau equation. A resonance instability occurs at a finite distance in Rayleigh number from the neutral curve. It leads to two independent wave patterns propagating past each other and finally gives rise to vacillations of the amplitude of convection. Most of these features can be described to a good approximation by a system of three coupled amplitude equations. Time integrations based on a Galerkin expansion show transitions to chaotic convection at higher Rayleigh numbers.

PROPERTIES OF A LORENZ MODEL FOR CONVECTION IN A ROTATING FLUID LAYER

1992 ◽  
Vol 06 (16n17) ◽  
pp. 1055-1061
Author(s):  
GOVINDAN RAJESH ◽  
SUPREETI DAS ◽  
JAYANTA K. BHATTACHARJEE
Keyword(s):  
Limit Cycle ◽  
Fluid Layer ◽  
Stable Limit Cycle ◽  
Period Doubling ◽  
Finite Amplitude ◽  
Stable Limit ◽  
Rotating Fluid ◽  
Onset Of Convection ◽  
Rayleigh Numbers ◽  
Period Doubling Bifurcations

A Lorenz-like model due to Veronis for onset of convection in a rotating fluid layer is analysed for Rayleigh numbers higher than the point at which stationary convection occurs. The most outstanding feature is that for Taylor numbers above a critical value, the Hopf bifurcation does lead to a finite amplitude stable limit cycle via a hysteretic transition. This limit cycle undergoes a sequence of period doubling bifurcations to form a Feigenbaum attractor which then makes a transition to the Lorenz-like attractor.

Convection in a compressible fluid with infinite Prandtl number

1980 ◽  
Vol 96 (3) ◽  
pp. 515-583 ◽  
Author(s):  
Gary T. Jarvis ◽  
Dan P. Mckenzie
Keyword(s):  
Prandtl Number ◽  
Viscous Dissipation ◽  
Coefficient Of Thermal Expansion ◽  
Frictional Heating ◽  
Finite Amplitude ◽  
Two Dimensions ◽  
Adiabatic Temperature ◽  
Time Dependent ◽  
Dependent Manner ◽  
Rayleigh Numbers

An approximate set of equations is derived for a compressible liquid of infinite Prandtl number. These are referred to as the anelastic-liquid equations. The approximation requires the product of absolute temperature and volume coefficient of thermal expansion to be small compared to one. A single parameter defined as the ratio of the depth of the convecting layer,d, to the temperature scale height of the liquid,HT, governs the importance of the non-Boussinesq effects of compressibility, viscous dissipation, variable adiabatic temperature gradients and non-hydrostatic pressure gradients. Whend/HT[Lt ] 1 the Boussinesq equations result, but whend/HTisO(1) the non-Boussinesq terms become important. Using a time-dependent numerical model, the anelastic-liquid equations are solved in two dimensions and a systematic investigation of compressible convection is presented in whichd/HTis varied from 0·1 to 1·5. Both marginal stability and finite-amplitude convection are studied. Ford/HT[les ] 1·0 the effect of density variations is primarily geometric; descending parcels of liquid contract and ascending parcels expand, resulting in an increase in vorticity with depth. Whend/HT> 1·0 the density stratification significantly stabilizes the lower regions of the marginal state solutions. At all values ofd/HT[ges ] 0·25, an adiabatic temperature gradient proportional to temperature has a noticeable stabilizing effect on the lower regions. Ford/HT[ges ] 0·5, marginal solutions are completely stabilized at the bottom of the layer and penetrative convection occurs for a finite range of supercritical Rayleigh numbers. In the finite-amplitude solutions adiabatic heating and cooling produces an isentropic central region. Viscous dissipation acts to redistribute buoyancy sources and intense frictional heating influences flow solutions locally in a time-dependent manner. The ratio of the total viscous heating in the convecting system, ϕ, to the heat flux across the upper surface,Fu, has an upper limit equal tod/HT. This limit is achieved at high Rayleigh numbers, when heating is entirely from below, and, for sufficiently large values ofd/HT, Φ/Fuis greater than 1·00.

Finite-amplitude cellular convection in a fluidsaturated porous layer

1980 ◽  
Vol 373 (1753) ◽  
pp. 199-222 ◽  
Keyword(s):  
Rayleigh Number ◽  
Temperature Gradient ◽  
Heat Transport ◽  
Critical Rayleigh Number ◽  
Three Dimensional ◽  
Finite Amplitude ◽  
Onset Of Convection ◽  
Optimum Heat ◽  
Square Cells

The local nonlinear stability of thermal convection in fluid-saturated porous media, subjected to an adverse temperature gradient, is investigated. The critical Rayleigh number at the onset of convection and the corresponding heat transfer are determined. An approximate analytical method is presented to determine the form and amplitude of convection. To facilitate the determination of the physically preferred cell pattern, a detailed study of both two- and three-dimensional motions is made and a very good agreement with available experimental data is found. The finite-amplitude effects on the horizontal wavenumber, and the effect of the Prandtl number on the motion are discussed in detail. We find that, when the Rayleigh number is just greater than the critical value, two dimensional motion is more likely than three-dimensional motion, and the heat transport is shown to have two regions for n =1. In particular, it is shown that optimum heat transport occurs for a mixed horizontal plan form formed by the linear combination of general rectangular and square cells. Since an infinite number of steady-state finite-amplitude solutions exist for Rayleigh numbers greater than the critical number A c * , a relative stability criterion is discussed th at selects the realized solution as that having the maximum mean-square temperature gradient.

scholarly journals Large-scale mean patterns in turbulent convection

2015 ◽  
Vol 776 ◽  
pp. 96-108 ◽  
Author(s):  
Mohammad S. Emran ◽  
Jörg Schumacher
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Finite Amplitude ◽  
Mean Flow ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
Prandtl Numbers ◽  
Rayleigh Benard Convection ◽  
Rayleigh Numbers ◽  
Rayleigh Benard

Large-scale patterns, which are well-known from the spiral defect chaos (SDC) regime of thermal convection at Rayleigh numbers $\mathit{Ra}<10^{4}$, continue to exist in three-dimensional numerical simulations of turbulent Rayleigh–Bénard convection in extended cylindrical cells with an aspect ratio ${\it\Gamma}=50$ and $\mathit{Ra}>10^{5}$. They are revealed when the turbulent fields are averaged in time and turbulent fluctuations are thus removed. We apply the Boussinesq closure to estimate turbulent viscosities and diffusivities, respectively. The resulting turbulent Rayleigh number $\mathit{Ra}_{\ast }$, that describes the convection of the mean patterns, is indeed in the SDC range. The turbulent Prandtl numbers are smaller than one, with $0.2\leqslant \mathit{Pr}_{\ast }\leqslant 0.4$ for Prandtl numbers $0.7\leqslant \mathit{Pr}\leqslant 10$. Finally, we demonstrate that these mean flow patterns are robust to an additional finite-amplitude sidewall forcing when the level of turbulent fluctuations in the flow is sufficiently high.

Finite amplitude axisymmetric thermoconvective flows in a bounded cylindrical layer of fluid

1975 ◽  
Vol 71 (2) ◽  
pp. 209-229 ◽  
Author(s):  
G. S. Charlson ◽  
R. L. Sani
Keyword(s):  
Rayleigh Number ◽  
Cell Size ◽  
Critical Value ◽  
Finite Amplitude ◽  
Cylindrical Layer ◽  
Lateral Boundary ◽  
Galerkin’S Method ◽  
Galerkin's Method ◽  
Rayleigh Numbers ◽  
Increasing Function

Finite amplitude axisymmetric thermoconvective flows in a bounded cylindrical layer of fluid heated from beneath were calculated using Galerkin's method. Both systems with insulated and with conducting lateral boundaries were investigated for radius-to-depth ratios of 1, 2·25, 2·55 and 2·66. Flows bounded by a conducting lateral boundary were found to be unstable for Rayleigh numbers greater than 1·1 times the critical value. The cell size was found to be an increasing function of the Rayleigh number.

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