Laminar natural convection boundary layers on horizontal circular discs

1979 ◽  
Vol 30 (3) ◽  
pp. 427-435 ◽  
Author(s):  
Md. Zakerullah ◽  
J. A. D. Ackroyd
Keyword(s):  
Natural Convection ◽  
Boundary Layers ◽  
Convection Boundary ◽  
Laminar Natural Convection

Length of near-wall plumes in turbulent convection

2011 ◽  
Vol 685 ◽  
pp. 335-364 ◽  
Author(s):  
Baburaj A. Puthenveettil ◽  
G. S. Gunasegarane ◽  
Yogesh K. Agrawal ◽  
Daniel Schmeling ◽  
Johannes Bosbach ◽  
...  
Keyword(s):  
Natural Convection ◽  
Boundary Layers ◽  
Fluid Layer ◽  
Geometric Constraints ◽  
Turbulent Convection ◽  
Total Length ◽  
Convection Boundary ◽  
Laminar Natural Convection ◽  
Prandtl Numbers ◽  
Near Wall

AbstractWe present planforms of line plumes formed on horizontal surfaces in turbulent convection, along with the length of line plumes measured from these planforms, in a six decade range of Rayleigh numbers ($1{0}^{5} \lt \mathit{Ra}\lt 1{0}^{11} $) and at three Prandtl numbers ($\mathit{Pr}= 0. 7, 5. 2, 602$). Using geometric constraints on the relations for the mean plume spacings, we obtain expressions for the total length of near-wall plumes on horizontal surfaces in turbulent convection. The plume length per unit area (${L}_{p} / A$), made dimensionless by the near-wall length scale in turbulent convection (${Z}_{w} $), remains constant for a given fluid. The Nusselt number is shown to be directly proportional to ${L}_{p} H/ A$ for a given fluid layer of height $H$. The increase in $\mathit{Pr}$ has a weak influence in decreasing ${L}_{p} / A$. These expressions match the measurements, thereby showing that the assumption of laminar natural convection boundary layers in turbulent convection is consistent with the observed total length of line plumes. We then show that similar relationships are obtained based on the assumption that the line plumes are the outcome of the instability of laminar natural convection boundary layers on the horizontal surfaces.

A Multigrid Accelerated Code for Simulating Unsteady Conjugate Natural Convection Boundary Layers

2016 ◽  
Vol 846 ◽  
pp. 30-35
Author(s):  
Mehdi Khatamifar ◽  
Emma Lee Wood ◽  
Wen Xian Lin ◽  
David Holmes ◽  
Steven W. Armfield ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Layers ◽  
Numerical Study ◽  
Viscous Boundary Layer ◽  
Central Difference ◽  
Simulation Accuracy ◽  
Conjugate Natural Convection ◽  
Wide Range ◽  
Convection Boundary

This paper presents a numerical study on the flow dynamics and heat transfer behaviour of unsteady conjugate natural convection boundary layers (CNCBLs) in a partitioned, air filled square cavity. An unsteady two-dimensional multigrid-assisted solver is developed in the C#.NET programming language on stretched Cartesian meshes. The finite volume method is used to discretise the governing equations. To solve the coupled pressure and velocity, the SIMPLE algorithm is used, and to increase simulation accuracy the Adam-Bashforth, QUICK and central difference schemes are employed for time, convection, and diffusion terms respectively. The Poisson pressure equation is solved through the use of the multigrid method. The developed code is used to model CNCBLs which typically require a large amount of simulation time. The numerical results provide detailed descriptions of unsteady CNCBLs and associated heat transfer behaviour over a wide range of Ra, such as the thermal and viscous boundary layer thicknesses, temperature and velocity distributions, and maximum velocities within the CNCBLs.

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