5 research outputs found
Eddy Heat Conduction and Nonlinear Stability of a Darcy Lapwood System Analysed by the Finite Spectral Method
Get PDFA finite Fourier transform is used to perform both linear and nonlinear stability analyses of a Darcy-Lapwood system of convective rolls. The method shows how many modes are unstable, the wave number instability band within each mode, the maximum growth rate (most critical) wave numbers on each mode, and the nonlinear growth rates for each amplitude as a function of the porous Rayleigh number. Single amplitude controls the nonlinear growth rates and thereby the physical flow rate and fluid velocity, on each mode. They are called the flak amplitudes. A discrete Fourier transform is used for numerical simulations and here frequency combinations appear that the traditional cut-off infinite transforms do not have. The discrete show a stationary solution in the weak instability phase, but when carried past 2 unstable modes they show fluctuating motion where all amplitudes except the flak may be zero on the average. This leads to a flak amplitude scaling process of the heat conduction, producing an eddy heat conduction coefficient where a Nu-RaL relationship is found. It fits better to experiments than previously found solutions but is lower than experiments
On thermal convective instability in rotating fluids.
Get PDFDoctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available on the PDF
Proceedings of the First International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
Get PDF1st International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Kruger Park, 8-10 April 2002.This lecture is a principle-based review of a growing body
of fundamental work stimulated by multiple opportunities to
optimize geometric form (shape, structure, configuration,
rhythm, topology, architecture, geography) in systems for heat
and fluid flow. Currents flow against resistances, and by
generating entropy (irreversibility) they force the system global
performance to levels lower than the theoretical limit. The
system design is destined to remain imperfect because of
constraints (finite sizes, costs, times). Improvements can be
achieved by properly balancing the resistances, i.e., by spreading
the imperfections through the system. Optimal spreading means
to endow the system with geometric form. The system
construction springs out of the constrained maximization of
global performance. This 'constructal' design principle is
reviewed by highlighting applications from heat transfer
engineering. Several examples illustrate the optimized internal
structure of convection cooled packages of electronics. The
origin of optimal geometric features lies in the global effort to
use every volume element to the maximum, i.e., to pack the
element not only with the most heat generating components, but
also with the most flow, in such a way that every fluid packet is
effectively engaged in cooling. In flows that connect a point to
a volume or an area, the resulting structure is a tree with high conductivity
branches and low-conductivity interstices.tm201
2011 program of study : shear turbulence : onset and structure
Get PDFThe theme for the Program in Geophysical Fluid Dynamics for the summer of 2011 was
Shear Turbulence: onset and structure. Ten days of principal lectures by FabianWale e and
Rich Kerswell began the summer, and a large number of seminars on this and a variety of
other topics then continued through the eighth week. These lectures are presented in these
Proceedings and form (we believe) the most complete, connected account of this subject)
Eleven fellows from around the globe helped to record the principal lectures, and each
carried out a project of his/her own, presented in seminar during the tenth and nal week.
All these lectures and projects are also presented in this Proceedings volume.
The further seminars presented throughout the summer by visitors and (in some cases)
by GFD faculty are also listed here. The popular Sears Lecture was given by L. Mahadevan.
The title was On growth and form: geometry, physics and biology. It was indeed popular,
drawing a large and enthusiastic audience.Funding was provided by the National Science Foundation under Grant No. OCE-0824636 and the
Office of Naval Research under Contract No. N00014-09-1084
