自然界中存在很多的湍流熱對流現象。他們對於工業，科學與技術有著非常重要的影響。在本論文中我們利用多温度探头的技术研究了湍流熱對流的理想模型-湍流瑞利-伯納德對流中的大尺度環流在高普朗特數下的動力學特性。 / 實驗中，我们利用水和電子液體FC77 作為工作物質，獲得了普朗特數Pr 從5.3 到19.4. 瑞利數Ra 範圍8.3 × 10⁸ 2.94 × 10¹¹.我們用了一個寬高比Γ 為1 的圓柱形對流槽來研究大尺度環流的動力學特性。我們發現，在高普朗特數的時候，大尺度環流仍然是一個single roll. 這個與我們期望的是一樣的。大尺度環流的強度δ 的概率密度函數是一個高斯分佈。但是左邊的尾巴可以用一個指數函數來描述。我們也觀察到了大尺度環流傾向於呆在一個特定的角向位置。我們還發現，大尺度流動的角向運動具有擴散運動的特性。但是，用FC77 作為工作物質時，這個角向運動的擴散係數比用水作為工作物質時小兩個量級。實驗中測量到的雷諾數Re 和瑞利數Ra 之間的標度率與之前的實驗結果相符合。同時這個標度率也和Grossman-Lohse 模型的預測相符合。 / 大尺度流動豐富的動力學特性，比如說流動停止，流向反轉，扭轉還有平移振盪以及流動模式轉換，都可以在高普朗特數的時候觀察到。比較有趣的是我們發現流動停止在一個三維系統中既不依賴於Ra, 又不依賴於Pr. 這個結果和二維的瑞利-伯納德對流完全不同。 / Turbulent thermal convection is of tremendous importance to many areas of science, technology as well as the environment. In this thesis, the dynamics of the large-scale circulation (LSC) in turbulent Rayleigh-B´enard convection, which is an idealised model to study turbulent thermal convection problem, is investigated using the multi-thermal probe technique in the high Prandtl number Pr regime. / Using two kinds of working fluids, namely water and Fluorinert FC77, we achieved Pr from 5.3 to 19.4 and Rayleigh number Ra from 8.3×10⁸ to 2.94×10¹¹. The dynamics of the LSC is measured in an aspect ratio unity convection cell. It is found that the LSC in the high Pr regime is a single roll structure as expected. The probability distribution of the flow strength δ is a Gaussian distribution function with exponential tail to the left. The preferred orientation is also observed, which is revealed by the PDF of azimuthal orientation θ of the LSC. The azimuthal motion of the LSC is a diffusive process, which is the same as previous studies. However, we found that the diffusivity of the angular speed using FC77 as the working fluid is two orders smaller than using water as working fluid. The scaling of the measured Reynolds number Re number based on the oscillation frequency of the LSC with respect to Ra is in good agreement with previous experimental results and also Grossman-Lohse model prediction. / The abundant dynamical features of the LSC, such as cessations, flow reversals, torsional and sloshing oscillations and flow mode transitions are also observed in the high Pr regime. One surprising finding is that the cessation frequency of the LSC ,based on the statistics of the mid-height level of thermistors, is independent of both Ra and Pr, which is quite different from the (quasi) two-dimensional turbulent Rayleigh-B´enard convection. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Xie, Yichao = 高普朗特數瑞利-伯納德對流中大尺度環流動力學特性研究 / 謝毅超. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 53-57). / Abstracts also in Chinese. / Xie, Yichao = Gao pu lang te shu Ruili-Bonade dui liu zhong da chi du huan liu dong li xue te xing yan jiu / Xie Yichao. / Abstract --- p.ii / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Natural convection and Rayleigh-B´enard convection --- p.1 / Chapter 1.2 --- Governing equation and control parameters of RB Convection --- p.2 / Chapter 1.3 --- The large-scale circulation in turbulent RB convection --- p.4 / Chapter 1.4 --- Motivation and organisation of this thesis --- p.6 / Chapter 2 --- Experimental Setup and Measurement Techniques --- p.7 / Chapter 2.1 --- The convection cell --- p.7 / Chapter 2.1.1 --- The conduction plate and sidewall --- p.7 / Chapter 2.1.2 --- Cooling and heating system --- p.7 / Chapter 2.1.3 --- Level of the convection system --- p.7 / Chapter 2.2 --- The thermistor and it’s calibration --- p.9 / Chapter 2.3 --- Multi-thermal-probe technique --- p.10 / Chapter 2.4 --- Data analysis method --- p.12 / Chapter 2.4.1 --- Sinusoidal fitting method (SF method) --- p.12 / Chapter 2.4.2 --- Temperature extrema extraction method (TEE method) --- p.13 / Chapter 2.5 --- Physical properties of FC77 --- p.14 / Chapter 2.6 --- Other equipment --- p.15 / Chapter 3 --- Dynamics of LSC in high Pr turbulent RBC --- p.16 / Chapter 3.1 --- Background --- p.16 / Chapter 3.2 --- Experimental setup and data analyse method --- p.18 / Chapter 3.3 --- Results and discussion --- p.19 / Chapter 3.3.1 --- General features of the LSC --- p.19 / Chapter 3.3.2 --- Statistics of the angular speed --- p.23 / Chapter 3.3.3 --- Reynolds number Re --- p.30 / Chapter 3.3.4 --- Cessations, reversals and flow mode transitions --- p.34 / Chapter 3.3.5 --- Torsional and sloshing motions of the LSC --- p.42 / Chapter 3.4 --- Summary --- p.48 / Chapter 4 --- Conclusion and outlook --- p.51 / Chapter 4.1 --- Conclusion --- p.51 / Chapter 4.2 --- Outlook --- p.51 / Bibliography --- p.53
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328800 |
| Date | January 2012 |
| Contributors | Xie, Yichao., Chinese University of Hong Kong Graduate School. Division of Physics. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xiv, 57 leaves) : ill. (some col.) |
| 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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