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ThesisReykjavík University>Tækni- og verkfræðideild>MSc verkefni>

Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/13208

Title

On the Effects of Buoyancy on Passive Particle Motions in the Convective Boundary Layer from the Lagrangian Viewpoint

Published
September 2012
Abstract

Mechanical turbulence and convection are combined together in this project to make it a real scientific and engineering challenge. Thees two natural phenomenon are put together under experimental investigations inside the flow facility at the Laboratory for Fundamental Turbulence Research (LFTR) at Reykjavik University. The aim of this research is to study the effects of the buoyancy on passive particle motions in the convective boundary layer, and on the intermittent nature of the small scale structures present in such region. The region of interest is located at 15\,mm above the heated wall. Particle image velocimetry (Eulerian frame of reference) and Particle tracking velocimetry (Lagrangian frame of reference) are the measurements techniques used in this present work. Our flow is found to be approximatively homogeneous with a slight variation in the direction of the heat flow and anisotropic, with a Taylor Reynolds number, R_\lambda = 200, local Rayleigh number based on the thickness of the boundary layer, Ra_delta = 3x10^5$ and local Prandtl number, Pr = 6.77. Our focus is on small structures of homogeneous and anisotropic turbulence, ranging from the smallest scale present in the dissipative range, $\eta $ (Kolmogorov scale) to the to energy containing scales in the inertial subrange \eta << r << L . Eulerian and Lagrangian experiments were conducted at the region of interest with an imposed mean thermal gradient of various intensities. The production and generation of stable mean thermal gradient in the box-turbulence was done by a developed mathematical model which had predicted the shape of the mean temperature profile of our flow. New heating/cooling system was designed and implemented to generate the convective turbulence. We found that, in the presence of the buoyancy force, a new dynamic regime arises and the intermittency becomes very high which will increase the particle-particle interaction and therefore will increase their coalescence and rate of collisions.

Issued Date
01/10/2012


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