In this thesis, we attempt to address some of these questions. First, we have devised a scheme to extract information of the plumes from simultaneous velocity and temperature measurements. Our method makes explicit use of the physical intuition that the velocity of the buoyant structures, e.g. plumes, should be related to the temperature fluctuation, in some apriori unknown manner as they are generated by buoyancy. Our scheme involves a decomposition of the local velocity measurement into two parts. The part that is correlated with some function of the temperature fluctuation measured at the same time is taken as the velocity of the plumes. Applying this scheme to measurements taken at the center and near the sidewall of the convection cell where the dominant buoyant structures are plumes, we have found the temperature dependence of the plume velocity at these two locations and understood our results from the equations of motion. Using these results of the temperature dependence of the plume velocity, we (i) conclude that heat is not mainly transported through the central region of the convection cell and (ii) obtain a relation between the scaling behavior of the plume velocity structure functions and the temperature structure functions that is different from what is implied by Bolgiano-Obukhov scaling. Then we have studied the possible effects of the large-scale mean circulation on the velocity and temperature statistics using simplified shell models of turbulent convection. We have introduced a large-scale mean flow into two shell models and found that its presence does not change the scaling behavior of velocity and temperature. / In turbulent thermal convection, velocity and temperature measurements taken at a point display complex fluctuations in time. On the other hand, visualization of the flow reveals recurring coherent structures. One prominent flow structure is a plume, which is generated from the thermal boundary layers by buoyancy. Another flow structure is a large-scale mean circulation that spans the entire convection cell. At least two strategies can be employed to study turbulent thermal convection or turbulent flows in general. One is to analyze and understand the fluctuations of the local measurements. The other is to characterize the coherent structures and study and understand their dynamics. These two approaches are not independent but provide complementary knowledge of the flows. Interesting questions hence include whether and how information about the ordered flow structures can be extracted from the fluctuating local measurements and how the presence of the ordered flow structures might affect the statistics of the fluctuations. / Guo, Hao = 热对流湍流中的统计特性与结构 / 郭昊. / "January 2007." / Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 6036. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 62-66). / 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. / Title and abstract in English and Chinese. / School code: 1307. / Guo, Hao = Re dui liu tuan liu zhong de tong ji te xing yu jie gou / Guo Hao.

Airwakes are shed behind the ship’s superstructure and represent a highly turbulent and rapidly distorting flow field. This flow field severely affects pilot’s workload and such helicopter shipboard operations. It requires both the one-point statistics of autospectrum and the two-point statistics of coherence (normalized cross-spectrum) for a relatively complete description. Recent advances primarily refer to generating databases of flow velocity points through experimental and computational fluid dynamics (CFD) investigations, numerically computing autospectra along with a few cases of cross-spectra and coherences, and developing a framework for extracting interpretive models of autospectra in closed form from a database along with an application of this framework to study the downwash effects. By comparison, relatively little is known about coherences. In fact, even the basic expressions of cross-spectra and coherences for three components of homogeneous isotropic turbulence (HIT) vary from one study to the other, and the related literature is scattered and piecemeal. Accordingly, this dissertation begins with a unified account of all the cross-spectra and coherences of HIT from first principles. Then, it presents a framework for constructing interpretive coherence models of airwake from a database on the basis of perturbation theory. For each velocity component, the coherence is represented by a separate perturbation series in which the basis function or the first term on the right-hand side of the series is represented by the corresponding coherence for HIT. The perturbation series coefficients are evaluated by satisfying the theoretical constraints and fitting a curve in a least squares sense on a set of numerically generated coherence points from a database. Although not tested against a specific database, the framework has a mathematical basis. Moreover, for assumed values of perturbation series constants, coherence results are presented to demonstrate how coherences of airwakes and such flow fields compare to those of HIT. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Zhou Sheng-qi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 66-70). / Text in English; abstracts in English and Chinese. / Zhou Sheng-qi. / Abstract (in Chinese) --- p.i / Abstract (in English) --- p.ii / Acknowledgement --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.viii / Chapter / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Turbulence: a Universal Problem --- p.1 / Chapter 1.2 --- Rayleigh-Benard Convection --- p.2 / Chapter 1.2.1 --- The History of Rayleigh-Benard Convection --- p.2 / Chapter 1.2.2 --- The Dimensionless Parameters --- p.4 / Chapter 1.2.3 --- The Physical Picture of Turbulent Convection --- p.5 / Chapter 1.3 --- Motivation of This Study --- p.8 / Chapter 2. --- Theoretical Base and Experimental Setup --- p.11 / Chapter 2.1 --- The Rayleigh-Benard problem --- p.11 / Chapter 2.1.1 --- The Boussinesq approximation --- p.11 / Chapter 2.1.2 --- The Convection Equation --- p.13 / Chapter 2.2 --- Experimental Setup and Measurement --- p.14 / Chapter 2.2.1 --- The Convection Cell --- p.14 / Chapter 2.2.2 --- The Power Supply and the Refrigerated Recirculator --- p.19 / Chapter 2.2.3 --- The Temperature Probes --- p.19 / Chapter 2.2.4 --- The Temperature Measurement System --- p.20 / Chapter 2.2.5 --- Building up the Convection State --- p.25 / Chapter 3. --- Temperature Power Spectra and the Viscous Boundary Layer in the Thermal Turbulence --- p.27 / Chapter 3.1 --- The Power Spectra Method --- p.27 / Chapter 3.2 --- The Suspicions of the Power Spectra Method --- p.30 / Chapter 3.3 --- Discussion of the Experimental Results --- p.32 / Chapter 3.4 --- Summary --- p.39 / Chapter 4. --- The Correlation Function of Temperature --- p.40 / Chapter 4.1 --- Preparation of Experiment --- p.41 / Chapter 4.1.1 --- Apparatus --- p.41 / Chapter 4.1.2 --- Definition of correlation function --- p.41 / Chapter 4.2 --- Results and Discussion --- p.44 / Chapter 4.2.1 --- The Delay Time (¡’0) --- p.47 / Chapter 4.2.2 --- The Maximum Correlation Coefficient (R) --- p.52 / Chapter 4.2.3 --- The Half Width (¡’h) --- p.58 / Chapter 4.3 --- Summary --- p.61 / Chapter 5. --- Conclusions --- p.63 / References --- p.66

Shang Xiandong. / "September 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 141-146). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.