Laser-Doppler Measurements of the Velocity Along a Heated Vertical Wall of a Rectangular Enclosure

1983 ◽  
Vol 105 (4) ◽  
pp. 782-788 ◽  
Author(s):  
H. Ozoe ◽  
M. Ohmuro ◽  
A. Mouri ◽  
S. Mishima ◽  
H. Sayama ◽  
...  
Keyword(s):  
Numerical Solutions ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Laser Doppler ◽  
Central Core ◽  
Heated Wall ◽  
Critical Test ◽  
Three Dimensional Flow ◽  
Rectangular Enclosure ◽  
First Time

The horizontal and vertical velocity profiles near a heated vertical wall of rectangular enclosure were measured for the laminar regime of natural convection with a laser-Doppler anemometer. The horizontal temperature profiles near the heated wall were measured with a thermocouple. An almost perfect two-dimensional mode of flow was confirmed for the central regime of the box. A minimum in the temperature profile between the hot wall and the thermally stratified central core resulted in a downward flow just outside the boundary layer of upward flow, but the central core was stagnant. Visualization of the flow with a phenolphtalein tracer confirmed the two-dimensionality of the flow along the vertical heated wall and revealed a zone of three-dimensional flow in the form of spiral streaklines along the insulated top plate toward the opposing cooled vertical wall. Measurements such as these provide for the first time the basis for a critical test of the accuracy of numerical solutions.

Three-Dimensional Natural Convective Flow in a Rectangular Enclosure With a Rectangular Heated Section on One Vertical Wall and With the Other Vertical Walls Cooled

2008 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Abdulrahim Kalendar ◽  
Thomas M. Simko
Keyword(s):  
Convective Flow ◽  
Vertical Wall ◽  
Three Dimensional ◽  
The Other ◽  
Heated Wall ◽  
Governing Equations ◽  
Vertical Sidewall ◽  
Rectangular Enclosure ◽  
Wide Range ◽  
Vertical Walls

Three-dimensional natural convective flow in a rectangular enclosure with vertical sidewalls and horizontal top and bottom surfaces has been considered. A heated rectangular element is mounted in the middle of one vertical wall of the enclosure, the remainder of this wall being adiabatic. The remaining vertical walls are cooled to a uniform low temperature. The horizontal top and bottom walls are adiabatic. The flow has been assumed to be steady and laminar. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. Radiation effects have been neglected. The numerical solution was obtained using the governing equations written in terms of dimensionless variables. The enclosure height, H′, was used as the characteristic length scale and the difference between the temperatures of the hot wall section and the cooled walls were used as the characteristic temperature scale. The dimensionless governing equations have been solved using FIDAP, a commercial software package that employs the finite element method. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless height of the heated wall section compared to the overall enclosure height; the dimensionless width of the heated wall section compared to its height; the dimensionless width of the enclosure between the vertical sidewall on which the heated wall section is mounted and the opposite vertical sidewall, and the dimensionless width of the enclosure between the other two vertical sidewalls. Because of the application being considered, results have only been obtained for Pr = 0.7. Attention has been restricted to the case where the dimensionless width of the enclosure between the vertical sidewall on which the heated wall section is mounted and the opposite vertical sidewall is 0.5 and where the dimensionless width of the enclosure between the other two vertical sidewalls is 1.0. A wide range of the other parameters has been considered particular attention having been given to the effect of the dimensionless width of the heated wall section compared to its height on the mean Nusselt number for the heated wall section.

Visualization and Prediction of Natural Convection of Water Near Its Density Maximum in a Tall Rectangular Enclosure at High Rayleigh Numbers

2000 ◽  
Vol 123 (1) ◽  
pp. 84-95 ◽  
Author(s):  
C. J. Ho ◽  
F. J. Tu
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Convection Flow ◽  
Oscillatory Convection ◽  
Uniform Temperature ◽  
Density Maximum ◽  
Rectangular Enclosure ◽  
Rayleigh Numbers

An experimental and numerical investigation is presented concerning the natural convection of water near its maximum-density in a differentially heated rectangular enclosure at high Rayleigh numbers, in which an oscillatory convection regime may arise. The water in a tall enclosure of Ay=8 is initially at rest and at a uniform temperature below 4°C and then the temperature of the hot vertical wall is suddenly raised and kept at a uniform temperature above 4°C. The cold vertical wall is maintained at a constant uniform temperature equal to that of the initial temperature of the water. The top and bottom walls are insulated. Using thermally sensitive liquid crystal particles as tracers, flow and temperature fields of a temporally oscillatory convection was documented experimentally for RaW=3.454×105 with the density inversion parameter θm=0.5. The oscillatory convection features a cyclic sequence of onset at the lower quarter-height region, growth, and decay of the upward-drifting secondary vortices within counter-rotating bicellular flows in the enclosure. Two and three-dimensional numerical simulations corresponding to the visualization experiments are undertaken. Comparison of experimental with numerical results reveals that two-dimensional numerical simulation captures the main features of the observed convection flow.

Three-Dimensional Flow Effects on Convective Heat Transfer From a Window Covered by a Simple Plane Blind With No Top Covering

2006 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Approximate Model ◽  
Conductive Heat ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Effects

Most studies of convective heat transfer in window-blind systems assume that the flow over the window-blind arrangement is two-dimensional. In some cases, however, three-dimensional flow effects can become important. The present study was undertaken to determine how significant such effects can be for the particular case of a window covered by a simple plane blind. Only convective heat transfer has been considered. The situation considered is only an approximate model of the real window-blind situation. The window is represented by a rectangular vertical isothermal wall section embedded in a large vertical adiabatic plane wall surface and exposed to a large surrounding "room" in which the temperature is lower than the window temperature. The plane blind is represented by a thin vertical wall having the same size as the "window" which offers no resistance to heat transfer across it and in which conductive heat transfer is negligible. The gaps between the blind and the window at the sides and at the top of the window-blind system are assumed to be open. The flow has been assumed to be laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. The solution has been obtained by numerically solving the three-dimensional governing equations written in dimensionless form. The effects of the dimensionless governing variables on the window Nusselt number have been numerically examined.

Instability in a viscous flow driven by streamwise vortices

2001 ◽  
Vol 432 ◽  
pp. 127-166 ◽  
Author(s):  
K. W. BRINCKMAN ◽  
J. D. A. WALKER
Keyword(s):  
Boundary Layer ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Wall Layer ◽  
External Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Wall Flow ◽  
Turbulent Wall ◽  
Near Wall

Unsteady separation processes at large finite, Reynolds number, Re, are considered, as well as the possible relation to existing descriptions of boundary-layer separation in the limit Re → ∞. The model problem is a fundamental vortex-driven three-dimensional flow, believed to be relevant to bursting near the wall in a turbulent boundary layer. Bursting is known to be associated with streamwise vortex motion, but the vortex/wall interactions that drive the near-wall flow toward breakdown have not yet been fully identified. Here, a simulation of symmetric counter-rotating vortices is used to assess the influence of sustained pumping action on the development of a viscous wall layer. The calculated solutions describe a three-dimensional flow at finite Re that is independent of the streamwise coordinate and consists of a crossflow plane motion, with a developing streamwise flow. The unsteady problem is constructed to mimic a typical cycle in turbulent wall layers and numerical solutions are obtained over a range of Re. Recirculating eddies develop rapidly in the near-wall flow, but these eddies are eventually bisected by alleyways which open up from the external flow region to the wall. At sufficiently high Re, an oscillation was found to develop in the streamwise vorticity field near the alleyways with a concurrent evolution of a local spiky behaviour in the wall shear. Above a critical value of Re, the oscillation grows rapidly in amplitude and eventually penetrates the external flow field, suggesting the onset of an unstable wall-layer breakdown. Local zones of severely retarded streamwise velocity are computed which are reminiscent of the low-speed streaks commonly observed in turbulent boundary layers. A number of other features also bear a resemblance to observed coherent structure in the turbulent wall layer.

Wavelet-based adaptive simulations of three-dimensional flow past a square cylinder

2014 ◽  
Vol 748 ◽  
pp. 433-456 ◽  
Author(s):  
Giuliano De Stefano ◽  
Oleg V. Vasilyev
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Adaptive Methods ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Eddy Simulation ◽  
Experimental Findings ◽  
Bluff Body Flows

AbstractThe wavelet-based eddy capturing approach is extended to three-dimensional bluff body flows, where the flow geometry is enforced through Brinkman volume penalization. The wavelet-collocation/volume-penalization combined method is applied to the simulation of vortex shedding flow behind an isolated stationary prism with square cross-section. Wavelet-based direct numerical simulation is conducted at low supercritical Reynolds number, where the wake develops fundamental three-dimensional flow structures, while wavelet-based adaptive large-eddy simulation supplied with the one-equation localized dynamic kinetic-energy-based model is performed at moderately high Reynolds number. The present results are in general agreement with experimental findings and numerical solutions provided by classical non-adaptive methods. This study demonstrates that the proposed hybrid methodology for modelling bluff body flows is feasible, accurate and efficient.

Effect of Sinusoidal Oscillatory Flow on a Vertical Wall-Mounted Cylinder

2020 ◽  
Author(s):  
HaKun Jang ◽  
Celalettin Emre Ozdemir ◽  
Mayank Tyagi ◽  
Jun-Hong Liang
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Finite Depth ◽  
Horseshoe Vortex ◽  
Vortex Structures ◽  
Navier Stokes ◽  
Wide Range ◽  
Sinusoidal Flow

Abstract The purpose of this study is to numerically investigate the bed shear stress and near-bed mixing due to coherent vortex structures in the vicinity of a vertically wall-mounted circular cylinder subject to an imposed finite-depth oscillatory sinusoidal flow. Previous studies reveal that the Keulegan–Carpenter (KC) number influences the formation of lee-side wake vortex structures as well as the horseshoe vortex in front of a cylinder. Therefore, parametric studies in a moderately wide range of KC from 5 to 20 are numerically performed. In the present study, Direct Numerical Simulation (DNS) is conducted using the open-source software, OpenFOAM, that solves the three-dimensional unsteady incompressible Navier-Stokes equations using finite volume method. Nondimensional parameters used in the simulations are carefully chosen to represent the real physics. The numerical solutions are first validated using an analytical solution for the oscillating Stokes flow and the results are then systematically and quantitatively compared with the experimental measurements. The results show that the lee-side wake is significantly influenced by KC, and distinctive types of the lee-side wake are generated and classified based on KC. It is also found that both KC and the ratio of the thickness of the Stokes boundary layer to the water depth are heavily associated with the stability of the lee-side wake. In addition, the simulated size and lifespan of the horseshoe vortex agree well with the experimental data.

Heat Transfer in Discretely Heated Side-Vented Compact Enclosures by Combined Conduction, Natural Convection, and Radiation

1999 ◽  
Vol 121 (4) ◽  
pp. 1002-1010 ◽  
Author(s):  
E. Yu ◽  
Y. K. Joshi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Radiative Heating ◽  
Computational Domain ◽  
Flow Recirculation ◽  
Discrete Heat Source ◽  
Rayleigh Numbers

A three-dimensional investigation of combined conduction, natural convection, and radiation in a side-vented compact enclosure is carried out. The focus of the study is on the enhancement of overall heat transfer through the opening, and the roles of the various modes in achieving it. A discrete heat source, flush-mounted centrally on a vertical substrate, is placed in the enclosure with a single rectangular opening on the opposite vertical wall. Steady-state computations are carried out for Rayleigh numbers, Ra, at 2.6 × 106 and 2.0 × 107. The results show that radiation plays a significant role in the overall heat transfer, and the radiative transport is even more pronounced for lower Ra. It is found that natural convection is weakened by radiation, however, contrary to the existing studies on top vented enclosures, the overall heat transfer is enhanced when radiation is included in the computations. Flow recirculation by radiative heating of enclosure walls is predicted, and is also observed experimentally. Heat spreading in the substrate is found to effect both convection and radiation. The numerical solutions on an extended computational domain are found in good agreement with the experimental data, when the conjugate effects are accounted for.

Three-dimensional flow in a closed thermosyphon

1981 ◽  
Vol 109 ◽  
pp. 259-275 ◽  
Author(s):  
G. D. Mallinson ◽  
A. D. Graham ◽  
G. De Vahl Davis
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Exchange Process ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Transfer Rates ◽  
Dimensional Flow ◽  
Flow And Heat Transfer ◽  
Study Heat Transfer ◽  
Rayleigh Numbers

A numerical and experimental study has been made of the three-dimensional flow and heat transfer by natural convection in a closed, rectangular thermosyphon. At low Rayleigh numbers, the flows in the two halves of the cavity remain separate, with heat transfer across the mid-height plane occurring only by conduction. At increasing Rayleigh numbers, an exchange process of increasing complexity occurs. The numerical solutions were used to explore this process and to predict flow patterns which were found to resemble closely those observed during previous investigations of cylindrical thermosyphons. The results were verified by a flow visualization study. Heat-transfer rates are presented and augment previous data for higher values of the governing parameters.

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