Direct real-space multi-point measurements of the velocity and temperature fields were carried out in various places of the convection cell. In the central region of the cell it is found that both velocity and temperature exhibit the same scaling behavior that one would find for the velocity and for a passive scalar in homogeneous and isotropic Navier-Stokes turbulence. Near the cell's sidewall where thermal plumes abound, vertical velocity and temperature exhibit different scalings. A model, taking into account both buoyancy and energy dissipation, is proposed and its predictions agree well with the sidewall experimental results. / This thesis aims to address three key issues in convectioe thermal turbulence: heat transport, statistics of turbulent fluctuations of the velocity and temperature fields, and flow dynamics. / Through measurement of 2D velocity at different cross sections of the cylindrical cell with Gamma = 1, we investigate the 3D flow structures and dynamics of turbulent thermal convection. Our result reveals how thermal plumes synchronize their emissions and organize their motions spatially between the top and bottom plates, leading to an oscillatory motion in the bulk region of the fluid. In Gamma = 0.5 small cell, we successfully identified the relationship between 2D instantaneous velocity map and the time-averaged 3D flow pattern. This experiment also showed that a particular value of Nu can be unambiguously associated with a specific large-scale flow mode in the convection cell. By taking into account the effects of the evolution in the circulation path of the mean wind and of the counterflow, we provide a solution to the riddle about the scaling exponent dispersion of the Reynolds number Re with Ra and show that the scaling exponent has a universal value of 0.5. / To study the confinement effect on heat transport at high levels of turbulence, we conducted high precision measurements of the Nusselt number Nu as a function of the Rayleigh number Ra in a 1 m diameter cylindrical cell filled with water with aspect ratio Gamma = 0.67, l, 2, 5, 10, 20. The measurements were conducted at the Prandtl number Pr ≃ 4 with Ra varying from 1 x 10 7 to 5 x 1012. It is found that Nuinfinity can be described by a combination of two power laws for all aspect ratios, and that the asymptotic large Gamma behavior may have been reached for Gamma ≥ 10. By studying the statistics of temperature fluctuations inside the conducting plates, we found that the product of temperature skewness and the skewness of temperature time derivative may be used to quantify the intensity of plume emissions. / Sun Chao = 熱湍流對流的實驗研究 / 孙超. / "July 2006." / Adviser: Keqing Xia. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1697. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 132-140). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / School code: 1307. / Sun Chao = Re tuan liu dui liu de shi yan yan jiu / Sun Chao.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_343891 |
| Date | January 2006 |
| Contributors | Sun, Chao, Chinese University of Hong Kong Graduate School. Division of Physics. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (xvii, 140 p. : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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