Three-dimensional convection regimes in a cubical cavity

Nonlinear three-dimensional convection regimes in a cubical cavity heated from below are studied numerically for small and moderate supercriticalities and different values of the Prandtl number Pr. The cases of adiabatic and perfectly heat-conducting lateral cavity boundaries are considered. The structure of different supercritical motions and their stability are investigated. The existence of different kinds of convective structures is detected over a wide range of governing parameters.     

Vibrational thermal convection in a rectangular cavity

Vibrational thermal convection in a rectangular cavity under conditions of weightlessness is studied. Some equilibrium configurations were obtained in earlier papers of two of the authors [1, 2] and their linear stability investigated. In the present paper, a numerical investigation is made of the developed vibrational convection which arises under conditions when equilibrium is impossible. The structure of the average vibrational-convective flows and the characteristics of the heat transfer are determined. The change of regimes and the connection with the stability problem are discussed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 94–99, July–August, 1982.     

Nonsteady-state thermal convection in a spherical cavity

Three-dimensional axisymmetrical convection in a spherical cavity is examined. The general heat-transfer condition is stipulated on the boundary of the spherical cavity. A method of finite differences is used for the solution.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 118–124, July–August, 1970.The authors thanks G. Z. Gershuni and E. M. Mukhovitskii for their help in this work.     

Bifurcation analysis for thermal convection in a rotating porous layer

The linear and weakly nonlinear thermal convection in a rotating porous layer is investigated by constructing a simplified model involving a system of fifth-order nonlinear ordinary differential equations. The flow in the porous medium is described by Lap wood-Brinkman-extended Darcy model with fluid viscosity different from effective viscosity. Conditions for the occurrence of possible bifurcations are obtained. It is established that Hopf bifurcation is possible only at a lower value of the Rayleigh number than that of simple bifurcation. In contrast to the non-rotating case, it is found that the ratio of viscosities as well as the Darcy number plays a dual role on the steady onset and some important observations are made on the stability characteristics of the system. The results obtained from weakly nonlinear theory reveal that, the steady bifurcating solution may be either sub-critical or supercritical depending on the choice of physical parameters. Heat transfer is calculated in terms of Nusselt number.     

Transient free convection flow between long vertical parallel plates with ramped wall temperature at one boundary in the presence of thermal radiation and constant mass diffusion

The unsteady laminar free convection flow between two long vertical parallel plates with ramped wall temperature at one boundary has been investigated in the presence of thermal radiation and chemical species concentration. The exact solutions of the momentum, energy and concentration equations have been obtained using the Laplace transform technique. The velocity and temperature profiles, skin-friction and Nusselt number variations are shown graphically and the numerical values of the volume flow rate, the total heat rate and species rate added to the fluid are presented in a table. The influence of different system parameters such as the radiation parameter (R), buoyancy ratio parameter (N), Schmidt number (Sc) and time (t) has been analyzed carefully. A critical analysis of the coupled heat and mass transfer phenomena is provided. The free convective flow due to ramped wall temperature has also been compared with the baseline case of flow due to constant wall temperature.     

Laminar thermal convection in rotating cavity between two disks

In solving several technical problems it is necessary to know what takes place in a closed rotating axisymmetric cavity filled with a nonuniformly heated viscous fluid. Such cavities are encountered, for example, in the rotors of steam and gas turbines. The thermal convection in these cavities is studied for a definite temperature condition of the rotors: in [1, 2] some qualitative considerations are presented, and quantitative estimates are given for thermal convection in cavities of turbine rotors; in [3,4] there is presented a very approximate calculation using the method of integral relations of the heat transfer coefficients in the case of a narrow cavity between two rotating disks which have different temperatures. We note that the thermal convection effect in a rotating cavity may be utilized in various technical devices, for example, in equipment for separating isotopes, etc. [5], A solution is presented for the problem of laminar thermal convection in a narrow cavity between two disks which are rotating with the same velocity and which have different temperatures which are constant along the radius. In the case of the narrow cavity we can neglect the influence of the cylindrical cavity rim on the flow in primary portion of the cavity (see [6]); therefore it is sufficient to solve the self-similar problem for two infinite disks.In conclusion I would like to thank A. Z. Serazetdinov and V. L. Karaseva for carrying out the computer calculations.     

On hydromagnetic free convection in the presence of induced magnetic field

Free convection in an electrically conducting fluid in a vertical channel under the action of an applied magnetic field has been discussed. The induced magnetic field has been included in the flow analysis. The equations describing the transport processes have been solved numerically. The effects of these processes, parameterized by a number of non-dimensional parameters have been discussed on the developing velocity and induced magnetic field profiles.     

Vibrational thermal convection in a cavity executing high-frequency rocking motions

The vibrational thermal convection in a cavity executing high-frequency rocking motions is investigated. The equations of vibrational convection are obtained by the method of averaging. It is shown that rocking motions lead to some new and distinctive effects. The convective stability in a plane layer in the presence of such vibrations is investigated on the basis of the obtained equations. A comparison with known experimental data is made. The results of experiments confirm the theoretical conclusions drawn on the basis of the averaged equations of vibrational convection.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 138–144, May–June, 1988.I thank E. M. Zhukhovitskii for helpful discussion.     

Investigation of low-intensity convection regimes in a rectangular cavity with a heat flux on the boundary

The characteristics of heat transfer during natural thermogravitational fluid convection of low intensity in a rectangular cavity heated from below (cooled from above) are investigated. Local convection effects are studied. The dependence of local superheating (supercooling) on the Grashof number and the cavity side ratio is found for single-, two-and three-vortex steady motions. The limits of the convection regimes are estimated.     

Nonlinear regimes of convection of an elasticoviscous fluid in a closed cavity heated from below

The two-dimensional thermal convection of a elasticoviscous fluid in a horizontal cylinder with a square cross-section heated from below is investigated. For describing the rheological properties of the fluid the Oldroyd model with the upper convective derivative is used. The investigation is carried out numerically using the finite-difference method. The instability limits of mechanical equilibrium with respect to monotonic and oscillatory perturbations are determined. Supercritical convection regimes are investigated numerically. Perm. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 5–11, July–August, 2000. This work was carried out with financial support from the Program of State Financial Support for Leading Science Schools (grant No. 96-15-96084).     

Thermohydrodynamic characteristics of combined double-diffusive radiation convection heat transfer in a cavity

This work deals with the numerical analysis of a radiating gas flow caused by both temperature and buoyancy concentration gradients in a square cavity; in this regard, the set of governing equations, including conservation of mass, momentum, species, and energy are solved by a numerical technique. In terms of radiation, since the fluid is considered as a semitransparent medium, the radiative term in the energy equation appears and is calculated by numerical solving of the radiative transfer equation (RTE). Furthermore, all of the surrounding cavity walls are considered to be opaque, gray, and diffuse with constant emissivity. All of the flow equations are solved by the finite difference method (FDM) and the RTE by the discrete ordinate one (DOM). In the present study, an attempt is made to verify the optical thickness effects on flow, thermal behavior, and mass transform in a cavity flow, such that reciprocating trends were seen in this manner. Our numerical results show that the thermal field in double-diffusive convection flow reaches very fast its steady-state situation in comparison to the concentration distribution. Besides, it is found that the thermohydrodynamic characteristics of a double-diffusive convection flow of a radiating gas are much affected by optical thickness.     

Effect of cavity inclination on a temperature and concentration controlled double diffusive convection at ice plate melting

This paper is concerned with the double diffusive convection due to the melting of an ice plate into a calcium chloride aqueous solution inside a rectangular cavity. It is mainly considered the effect of the cavity inclination on the melting rate and the mean melting Nusselt- and Sherwood-numbers, experimentally as well as numerically. The ice plate melts spontaneously with decreasing temperature at the melting front even if initially there does not exist a temperature difference between the ice and the liquid. The concentration- and temperature-gradients near the melting front induce double diffusive convection in the liquid, which will affect the melting rate. Experiments reveal that the mean melting mass increases monotonically with increasing cavity inclination. The numerical analysis based on the laminar assumption predicts well the melting mass in the range of =0–90°, however, under-predicts the melting mass in the range of =90–180° as compared with the experimental results.     

Magneto-hydrodynamic mixed convection of a power-law fluid past a stretching surface in the presence of thermal radiation and internal heat generation/absorption

The problem of magneto-hydrodynamic mixed convective flow and heat transfer of an electrically conducting, power-law fluid past a stretching surface in the presence of heat generation/absorption and thermal radiation has been analyzed. After transforming the governing equations with suitable dimensionless variables, numerical solutions are generated by an implicit finite-difference technique for the non-similar, coupled flow. The solution is found to be dependent on the governing parameters including the power-law fluid index, the magnetic field parameter, the modified Richardson number, the radiation parameter, the heat generation parameter, and the generalized Prandtl number. To reveal the tendency of the solutions, typical results for the velocity and temperature profiles, the skin-friction coefficient, and the local Nusselt number are presented for different values of these controlling parameters.     

Combined thermal radiation and natural convection in a cavity containing a discrete heater: Effects of nature of heating and heater aspect ratio

This paper investigates the interaction between thermal radiation and natural convection in an air filled square cavity with a discrete heater placed inside. The vertical walls of the cavity are cooled while the horizontal ones are insulated. Two types of the heater, viz., isothermal and heat generating are considered. The governing coupled nonlinear partial differential equations were solved using a finite volume method on a uniformly staggered grid system. The effects of the pertinent parameters such as the Rayleigh number, aspect ratio of the discrete heater and surface emissivity on the heat and fluid flow characteristics are investigated in detail. In general it is found that the overall heat transfer rate is enhanced with an increase of the surface emissivity and the Rayleigh number for both isothermal and heat generating heaters. Buoyancy induced flow gets augmented for the isothermal solid body whereas it is weakened for the heat generating body in the presence of radiation exchange.     

Interaction of turbulent natural convection and surface thermal radiation in inclined square enclosures

Two-dimensional numerical studies of flow and temperature fields for turbulent natural convection and surface radiation in inclined differentially heated enclosures are performed. Investigations are carried out over a wide range of Rayleigh numbers from 10⁸ to 10¹², with the angle of inclination varying between 0° and 90°. Turbulence is modeled with a novel variant of the k–ε closure model. The predicted results are validated against experimental and numerical results reported in literature. The effect of the inclination of the enclosure on pure turbulent natural convection and the latter’s interaction with surface radiation are brought out. Profiles of turbulent kinetic energy and effective viscosity are studied to observe the net effect on the intensity of turbulence caused by the interaction of natural convection and surface radiation. The variations of local Nusselt number and average Nusselt number are presented for various inclination angles. Marked change in the convective Nusselt number is found with the orientation of enclosure. Also analyzed is the influence of change in emissivity on the flow and heat transfer. A correlation relevant to practical applications in the form of average Nusselt number, as a function of Rayleigh number, Ra, radiation convection parameter, N _RC and inclination angle of the enclosure, φ is proposed.