Experimental Investigation of Natural Convection Losses From Open Cavities

1984 ◽  
Vol 106 (2) ◽  
pp. 333-338 ◽  
Author(s):  
C. F. Hess ◽  
R. H. Henze
Keyword(s):  
Natural Convection ◽  
Three Dimensional ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
Turbulence Flow ◽  
Temperature Boundary ◽  
Open Cavities ◽  
Rayleigh Numbers ◽  
Temperature Boundary Condition

Experimental results for natural convection in a cavity are reported. Both constrained and unconstrained cavity geometries were studied. Detailed velocity profiles were obtained using Laser doppler velocimetry for Rayleigh numbers between 3 × 1010 and 2 × 1011, corresponding to a constant elevated wall temperature boundary condition. Characteristics of two-dimensional and three-dimensional flows obtained with dye flow visualization are discussed, including boundary layer transition to turbulence, flow patterns in the cavity, and flow outside of the cavity. Local Nusselt number is correlated with local Rayleigh number for constrained and unconstrained cavities.

Final Design Parameter Settings for a Physically-Realizable Uniform Temperature Boundary Condition Specification on a Wall of an Enclosure

2013 ◽  
Author(s):  
P. Y. C. Lee ◽  
W. H. Leong
Keyword(s):  
Boundary Condition ◽  
Natural Convection ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Design Parameters ◽  
Uniform Temperature ◽  
Original Design ◽  
Temperature Boundary ◽  
Contact Width ◽  
Temperature Boundary Condition

Design parameters based on a three-dimensional internal natural convection heat transfer in a cubical apparatus are presented so that a uniform temperature boundary condition specification on a wall of the apparatus can be physically achieved. Preliminary temperature measurements based on the initial design of the apparatus where the uniform boundary condition was prescribed revealed that a temperature non-uniformity existed in the excess of 4% error. In order to complete the objective of the benchmark internal natural convection study, the apparatus had to be modified so that the temperature non-uniformity can be reduced to less than 1% error. It was decided that the original design be modified by simply adding two auxiliary heaters in the vicinity of the wall where the uniform temperature profile was desired. Before the implementation of the auxiliary heaters onto the apparatus, a detailed mathematical analysis was conducted to determine the position and the contact width of the heaters, and to establish an appropriate heat flux required to reduce the temperature non-uniformity to less than 1% along the wall of the apparatus. This analysis was achieved by using the approximate analytical temperature solution obtained from the boundary value problem of a plate (which is one part of the apparatus) with boundary conditions prescribed to model the auxiliary heaters. Previously, a specific set of design parameters were used that reduced the temperature non-uniformity to less than 1% along a wall of the modified cubical apparatus. As an extension to the previous work, this paper presents a generalized set of design parameters that can equally prescribe a physically-realizable uniform temperature setting along a wall of an enclosure to within 1% error. With the range of design parameters, this would enable any designer with the flexibility in choosing what parameters can be allocated based on their need.

The resonant-triad nonlinear interaction in boundary-layer transition

1987 ◽  
Vol 179 ◽  
pp. 227-252 ◽  
Author(s):  
F. T. Smith ◽  
P. A. Stewart
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Quantitative Agreement ◽  
Finite Amplitude ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
Structured Analysis

Recent controlled experiments by Kachanov & Levchenko (1984) and others indicate that, during some slower kinds of transition to turbulence in boundary layers, three-dimensionality can come into play initially as a resonant-triad phenomenon, depending on the disturbance sizes present. The triad interaction, suggested theoretically in the boundary-layer context by Craik (1971) and others, is studied in the present work by means of multi-structured analysis for high characteristic Reynolds numbers. A finite-amplitude/relatively high-frequency approach leads rationally to the nonlinear triad equations, solutions for which are then obtained analytically and computationally in certain central cases of interest (temporal and spatial). The solutions have a rather chaotic spiky appearance as continual energy exchange develops between the two- and three-dimensional nonlinear modes, whose large-scale response seems governed by inviscid dynamics but subject to important, continual ‘rejuvenation’ from small- (fast-) scale viscous action in-between. The three-dimensional growth rate is thereby increased, but not the two-dimensional. Subsequently the disturbed flow enters a higher-amplitude regime similar to that studied in some related papers by the authors and co-workers. Comparisons with the experiments are very supportive of the theory (in the small and in the large), yielding both qualitative and quantitative agreement.

Osborne Reynolds: Energy Methods in Transition and Loss Production: A Centennial Perspective

1995 ◽  
Vol 117 (1) ◽  
pp. 142-153 ◽  
Author(s):  
J. Moore ◽  
J. G. Moore
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Boundary Layer Transition ◽  
Turbulence Energy ◽  
Energy Methods ◽  
Layer Transition ◽  
Energy Balance Method ◽  
European Working ◽  
Transition Modeling

Osborne Reynolds’ developments of the concepts of Reynolds averaging, turbulence stresses, and equations for mean kinetic energy and turbulence energy are viewed in the light of 100 years of subsequent flow research. Attempts to use the Reynolds energy-balance method to calculate the lower critical Reynolds number for pipe and channel flows are reviewed. The modern use of turbulence-energy methods for boundary layer transition modeling is discussed, and a current European Working Group effort to evaluate and develop such methods is described. The possibility of applying these methods to calculate transition in pipe, channel, and sink flows is demonstrated using a one-equation, q-L, turbulence model. Recent work using the equation for the kinetic energy of mean motion to gain understanding of loss production mechanisms in three-dimensional turbulent flows is also discussed.

Numerical simulation of boundary-layer transition and transition control

1989 ◽  
Vol 199 ◽  
pp. 403-440 ◽  
Author(s):  
E. Laurien ◽  
L. Kleiser
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Transition Process ◽  
Numerical Results ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Layer Transition ◽  
Longitudinal Vortices ◽  
Tollmien Schlichting

The laminar-turbulent transition process in a parallel boundary-layer with Blasius profile is simulated by numerical integration of the three-dimensional incompressible Navier-Stokes equations using a spectral method. The model of spatially periodic disturbances developing in time is used. Both the classical Klebanoff-type and the subharmonic type of transition are simulated. Maps of the three-dimensional velocity and vorticity fields and visualizations by integrated fluid markers are obtained. The numerical results are compared with experimental measurements and flow visualizations by other authors. Good qualitative and quantitative agreement is found at corresponding stages of development up to the one-spike stage. After the appearance of two-dimensional Tollmien-Schlichting waves of sufficiently large amplitude an increasing three-dimensionality is observed. In particular, a peak-valley structure of the velocity fluctuations, mean longitudinal vortices and sharp spike-like instantaneous velocity signals are formed. The flow field is dominated by a three-dimensional horseshoe vortex system connected with free high-shear layers. Visualizations by time-lines show the formation of A-structures. Our numerical results connect various observations obtained with different experimental techniques. The initial three-dimensional steps of the transition process are consistent with the linear theory of secondary instability. In the later stages nonlinear interactions of the disturbance modes and the production of higher harmonics are essential.We also study the control of transition by local two-dimensional suction and blowing at the wall. It is shown that transition can be delayed or accelerated by superposing disturbances which are out of phase or in phase with oncoming Tollmien-Schlichting instability waves, respectively. Control is only effective if applied at an early, two-dimensional stage of transition. Mean longitudinal vortices remain even after successful control of the fluctuations.

Natural Convection from a Horizontal Cylinder—Laminar Regime

1981 ◽  
Vol 103 (3) ◽  
pp. 522-527 ◽  
Author(s):  
B. Farouk ◽  
S. I˙. Gu¨c¸eri
Keyword(s):  
Natural Convection ◽  
Horizontal Cylinder ◽  
Heat Transfer Characteristics ◽  
Convective Flows ◽  
Finite Difference Numerical Method ◽  
Temperature Boundary ◽  
Recirculation Zones ◽  
Boussinesq Fluid ◽  
Temperature Boundary Condition ◽  
Good Agreement

A finite-difference numerical method has been adopted to generate flow patterns and heat transfer characteristics for laminar, steady-state, two-dimensional natural convection around a circular cylinder submerged in an unbounded Boussinesq fluid. The approach allows the use of nonuniform as well as uniform specified temperature and heat flux distributions over the cylindrical surface. Part of the results are generated for reverse convective flows with recirculation zones which occur when part of the cylinder is below the ambient temperature while the remaining part is above. The results for uniform temperature boundary condition are in good agreement with the experimental data and other solutions available in literature.

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.

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