Zhao, Xiaozheng = 滑移邊界條件下湍流熱對流的實驗研究 / 趙晓争. / "September 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 52-57). / Abstracts in English and Chinese. / Zhao, Xiaozheng = Hua yi bian jie tiao jian xia tuan liu re dui liu de shi yan yan jiu / Zhao Xiaozheng. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iv / Contains --- p.iv / List of Figures --- p.vii / List of Tables --- p.xi / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Turbulence --- p.1 / Chapter 1.2 --- Turbulent Rayleigh-Benard Convection --- p.2 / Chapter 1.2.1 --- Physical Picture --- p.2 / Chapter 1.2.2 --- Governing Equations and Characteristic Parameters --- p.5 / Chapter 1.2.3 --- Nu Scaling --- p.7 / Chapter 1.2.4 --- Boundary Layer --- p.8 / Chapter 1.3 --- Motivations of the Present Work --- p.10 / Chapter 2 --- Experimental Setup --- p.13 / Chapter 2.1 --- The Convection Cell --- p.13 / Chapter 2.2 --- Temperature Probe and Translation Stage --- p.15 / Chapter 2.3 --- Calibration of the Thermistors --- p.17 / Chapter 2.4 --- Data Acquisition Units --- p.18 / Chapter 2.5 --- The Working Fluids --- p.19 / Chapter 2.6 --- Heat Leakage Prevention --- p.21 / Chapter 3 --- Heat Transfer and Thermal Boundary Layer Measurement --- p.23 / Chapter 3.1 --- The Setup and Experimental Procedure --- p.23 / Chapter 3.2 --- The Mean Temperature and Temperature Fluctuation Profiles across the Interfaces --- p.24 / Chapter 3.2.1 --- Profiles across the Water-FC77 Interface --- p.24 / Chapter 3.2.2 --- Profiles across the FC77-Mercury Interface --- p.27 / Chapter 3.3 --- Nu Results --- p.29 / Chapter 3.3.1 --- Results Obtained with Assumption of Pure Conduction --- p.30 / Chapter 3.3.2 --- Results from Mean Temperature Profile --- p.32 / Chapter 3.3.3 --- Comparison of the Two Methods --- p.33 / Chapter 3.4 --- Boundary Layer Thickness --- p.37 / Chapter 3.5 --- Summary --- p.39 / Chapter 4 --- Influence of Flow in the Water (Mercury) Layer on the FC77 Layer --- p.41 / Chapter 4.1 --- Experimental Setup --- p.41 / Chapter 4.2 --- Main Results --- p.42 / Chapter 4.3 --- Probability Density Function and Temperature Oscillation --- p.44 / Chapter 4.4 --- Summary --- p.50 / Chapter 5 --- Conclusions and Perspective --- p.51 / Chapter 5.1 --- Conclusions --- p.51 / Chapter 5.2 --- Perspective for Future Work --- p.52

Cai, Debin = 高普朗特數湍流對流中速度場和溫度場能量級串傳遞的實驗研究 / 蔡德斌. / "September 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 84-88). / Abstracts in English and Chinese. / Cai, Debin = Gao pu lang te shu tuan liu dui liu zhong su du chang he wen du chang neng liang ji chuan chuan di de shi yan yan jiu / Cai Debin. / Abstract (in English) --- p.i / Abstract (in Chinese) --- p.ii / Acknowledgements --- p.iii / Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.xv / Chapters / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Turbulence --- p.1 / Chapter 1.2 --- Turbulent Rayleigh-Benard Convection --- p.2 / Chapter 1.3 --- Small-Scale Properties of Turbulent Convection --- p.6 / Chapter 1.4 --- Motivations and structure of this thesis --- p.9 / Chapter 1.4.1 --- Motivations --- p.9 / Chapter 1.4.2 --- Organization of this thesis --- p.15 / Chapter 2. --- Experimental apparatus and techniques --- p.16 / Chapter 2.1 --- Turbulent Rayleigh-Benard convection cell --- p.16 / Chapter 2.2 --- The working fluid 1-Pentanol --- p.20 / Chapter 2.3 --- Technique and instruments in temperature structure function measurement --- p.21 / Chapter 2.3.1 --- Temperature detecting probe --- p.22 / Chapter 2.3.2 --- Electronic instruments for temperature measurement --- p.25 / Chapter 2.4 --- Technique and instruments in velocity structure function measurement --- p.28 / Chapter 3. --- Cascades of Temperature Fluctuations in High Prandtl Number Turbulent Convection --- p.31 / Chapter 3.1 --- Selection of the experimental parameters --- p.31 / Chapter 3.2 --- Temperature structure function at the cell centre --- p.33 / Chapter 3.2.1 --- Experiment arrangements --- p.34 / Chapter 3.2.2 --- Experiment results of temperature structure function at the cell centre --- p.37 / Chapter 3.3 --- Temperature structure function near the cell sidewall --- p.43 / Chapter 3.4 --- Intermittency in the high Pr number system --- p.49 / Chapter 3.5 --- Summary --- p.51 / Chapter 4. --- Cascades of Velocity Fluctuations in High Prandtl Number Turbulent Convection --- p.52 / Chapter 4.1 --- Experiment technique --- p.52 / Chapter 4.2 --- Velocity structure function at the cell centre --- p.54 / Chapter 4.2.1 --- Analysis with time average method only --- p.55 / Chapter 4.2.2 --- Homogeneity and isotropy at the cell centre --- p.61 / Chapter 4.2.3 --- Analysis with spatial average method --- p.65 / Chapter 4.3 --- Velocity structure function near the sidewall --- p.70 / Chapter 4.4 --- Summary --- p.75 / Chapter 5. --- Comparison between Different Experiments --- p.77 / Chapter 5.1 --- Comparison between High and Low Pr Number Cases --- p.77 / Chapter 5.2 --- Comparison between the Temperature and Velocity Structure Function Measurements in High Pr number System --- p.80 / Chapter 6. --- Conclusion --- p.82 / References --- p.84

The use of efficient basis functions to model and represent flows with internal sharp velocity gradients, such as shocks or eddy microfronts, are investigated. This is achieved by analysing artificial data, observed atmospheric turbulence data and by the use of a Burgers' equation based spectral model. The concept of an efficient decomposition of a function into a basis set is presented and alternative analysis methods are investigated. The development of a spectral model using a generalized basis for the Burgers' equation is presented and simulations are performed using a modified Walsh basis and compared with the Fourier (trigonometric) basis and finite difference techniques. The wavelet transform is shown to be superior to the Fourier transform or the windowed Fourier transform in terms of defining the predominant scales in time series of turbulent shear flows and in 'zooming in' on local coherent structures associated with sharp edges. Disadvantages are found to be its inability to provide clear information on the scale of periodicity of events. Artificial time series of varying amounts of noise added to structures of different scales are analyzed using different wavelets to show that the technique is robust and capable of detecting sharp edged coherent structures such as those found in shear driven turbulence. The Haar function is used as a wavelet to detect ubiquitous zones of concentrated shear in turbulent flows sometimes referred to as microfronts. The location and organization of these shear zones suggest that they may be edges of larger scale eddies. A wavelet variance of the wavelet phase plane is defined to detect and highlight events and obtain measures of predominant scales of coherent structures. Wavelet skewness is computed as an indicator of the systematic sign preference of the gradient of the transition zone. Inverse wavelet transforms computed at the dilation corresponding to the peak wavelet variance are computed and shown to contain a significant fraction of the total energy contained in the record. The analysis of data and the numerical simulation results are combined to propose that the sharp gradients normally found in shear induced turbulence significantly affect the nature of the turbulence and hence the choice of the basis set used for the simulation of turbulence. / Graduation date: 1991

The statistics describing variations of turbulent motions within the so called inertial range of length scales depend on the scale over which the motions are varying and the "average" rate at which the turbulent kinetic energy is being dissipated on the molecular scale. This hypothesis stemmed from the similarity arguments published by A. N. Kolmogorov in 1941 and implies specific scaling relations between the average amplitude and length scale of turbulent motions. Turbulent motions agree to a good approximation with Kolmogorov scaling provided the fluid flow admits to the underlying assumptions. More recently it has been recognized that the large spatial variations in the rate of turbulent kinetic energy dissipation may be a partial explanation for deviations from Kolmogorov scaling. This recognition is due in part to the observation that the total volume occupied by turbulent motions of a given scale decreases as the scale decreases. These observations imply that active small scale turbulence is intermittent. This study aims to better understand how scaling relations describing more active regions are different from the relations describing turbulence where the small scales are less active. The thesis is that the relations are different. An 18 hour segment of wind data measured in near-neutral stratification 45 meters above a relatively flat ground is analyzed. There is virtually no trend in the mean wind speed, so the describing statistics are essentially stationary. Small scale activity is measured in terms of the difference in wind speed (structure function) at a separation distance of 1/16 of a second, which translates to about a meter. The differences in wind speed are raised to the sixth power and then averaged over 4 second (50 meter) windows. Non-overlapping windows containing a local maximum in the averaged sixth order structure function form one (MASC) ensemble of more active small scale samples and the local minima form another (LASC) ensemble of less active small scale samples. The variations in wind speed as a function of length scale within each ensemble are decomposed five different ways. Each of the five decompositions obey scaling relationships that are approximately linear in log-log coordinates. The MASC and LASC ensembles include 32% and 46% of the record, respectively. The turbulent kinetic energy as a function of scale falls off at a slower rate in the MASC ensemble versus the LASC ensemble and in magnitude the energy is greater at all scales in the MASC ensemble. This implies the transfer rate of turbulent kinetic energy toward small scales is more rapid on average in the MASC samples. Samples in the MASC ensemble occupied 30% less of the record, implying the flattening effect on the spectral slope exhibited by the samples contained in the MASC ensemble is less influential than the steepening influence of samples of the type in the LASC ensemble. The results are robust with respect to the choice of a basis set in representing the variance as a function of scale. / Graduation date: 1994

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The Coriolis force has a subtle, but significant impact on the dynamics of geophysical and astrophysical flows. The Rossby number, Ro, is the nondimensional parameter measuring the relative strength of the Coriolis term to the nonlinear advection terms in the equations of motion. When the rotation is strong, Ro goes to zero and three-dimensional flows are observed to two-dimensionalize. The broad aim of this work is to examine the effect of the strength of rotation on the nonlinear dynamics of turbulent homogeneous flows. Our approach is to decompose the rotating turbulent flow modes into two classes: the zero-frequency 2-dimensional (2D) modes; and the high-frequency inertial waves (3D). / First, using numerical simulations of decaying turbulence over a large range of Ro we identified three regimes. The large Ro regime is similar to non-rotating, isotropic turbulence. The intermediate Ro regime shows strong 3D-to-2D energy transfers and asymmetry between cyclones (corotating) and anticyclones (couter-rotating), whereas at small Ro regime these features are much reduced. / We then studied discreteness effects and constructed a kinematic model to quantify the threshold of nonlinear broadening below which the 2D-3D interactions critical to the intermediate Ro regime are not captured. These results allow for the improvement of numerical studies of rotating turbulence and refine the comparison between results obtained in finite domains and theoretical results derived in unbounded domains. / Using equilibrium statistical mechanics, we examined the hypothesis of decoupling predicted in the small Ro regime. We identified a threshold time, t☆ = 2/Ro2, after which the asymptotic decoupling regime is no longer valid. Beyond t ☆, we show that the quasi-invariants of the decoupled model continue to constrain the system on the short timescales. / We found that the intermediate Ro regime is also present in forced turbulence and that interactions responsible for it are nonlocal. We explain a steep slope obtained in the 2D energy spectrum by a downscale enstrophy transfer. The energy of the 2D modes is observed to accumulate in the largest scales of the domain in the long-time limit. This is reminiscent of the "condensation" observed in classical forced 2D flows and magnetohydrodynamics.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1982. / Microfiche copy available in Archives and Science. / Supervised by Edward N. Lorenz. / Includes bibliographical references (leaves 141-145). / by Lin Ho. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1979. / Microfiche copy available in Archives and Science. / Bibliography : leaves 151-154. / by Joseph Stephen Scire. / M.S.

No description available.

For aerospace and naval applications where low radiated noise levels are a requirement, rotor noise generated by inflow turbulence is of great interest. Inflow turbulence is stretched and distorted as it is ingested into a thrusting rotor which can have a significant impact on the noise source levels. This thesis studies the distortion of subsonic, high Reynolds number turbulent flow, with viscous effects ignored, that occur when a rotor is embedded in a turbulent boundary layer. The analysis is based on Rapid Distortion Theory (RDT), which describes the linear evolution of turbulent eddies as they are stretched by a mean flow distortion. Providing that the gust does not distort the mean flow streamlines the solution for a mean flow with shear is found to be the same as the solution for a mean potential flow with the addition of a potential flow gust. By investigating the inflow distortion of small-scale turbulence for various simple flows and rotor inflows with weak shear, it is shown that RDT can be applied to incompressible shear flows to determine the flow distortion. It is also shown that RDT can be applied to more complex flows modeled by the Reynolds Averaged Navier Stokes (RANS) equations. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.