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An Investigation of Energy Dissipati...

Ni, Rui.

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An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants./
Author:	Ni, Rui.
Description:	141 p.
Notes:	Source: Dissertation Abstracts International, Volume: 73-08(E), Section: B.
Contained By:	Dissertation Abstracts International73-08B(E).
Subject:	Physics, Fluid and Plasma. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3504742
ISBN:	9781267259356

An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants.
Ni, Rui.

An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants. - 141 p.

Source: Dissertation Abstracts International, Volume: 73-08(E), Section: B.

Thesis (Ph.D.)--The Chinese University of Hong Kong (Hong Kong), 2011.

This thesis studies several important issues in turbulent Rayleigh-Benard (RB) convection: the energy dissipation rate, the acceleration statistics and reversals of the large scale flow; and investigates a long-standing question regarding the Kolmogorov constant, an important constant in the statistical theory of fluid turbulence.

ISBN: 9781267259356Subjects--Topical Terms:

1018402
Physics, Fluid and Plasma.

An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants.
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008 150210s2011 ||||||||||||||||| ||eng d
020 $a 9781267259356
035 $a (MiAaPQ)AAI3504742
035 $a AAI3504742
040 $a MiAaPQ $c MiAaPQ
100 1 $a Ni, Rui. $3 2102009
245 1 3 $a An Investigation of Energy Dissipation, Acceleration Statistics and Reversals in Turbulent Thermal Convection and of the Kolmogorov Constants.
300 $a 141 p.
500 $a Source: Dissertation Abstracts International, Volume: 73-08(E), Section: B.
500 $a Adviser: Keqing Xia.
502 $a Thesis (Ph.D.)--The Chinese University of Hong Kong (Hong Kong), 2011.
520 $a This thesis studies several important issues in turbulent Rayleigh-Benard (RB) convection: the energy dissipation rate, the acceleration statistics and reversals of the large scale flow; and investigates a long-standing question regarding the Kolmogorov constant, an important constant in the statistical theory of fluid turbulence.
520 $a Experimentally, the energy dissipation rate, the acceleration statistics, and the Kolmogorov constants are measured by the Lagrangian particle tracking velocimetry developed in a thermal convection system. The energy dissipation rate in the cell center epsilonupsilon,c was measured experimentally for the first time in RB convection, with varying Rayleigh number Ra, Prandtl number Pr, and system size H. The Ra- and H-dependency of the measured result are found to be consistent with a key assumption made for the bulk energy dissipation rate epsilonupsilon,bulk in the Grossmann-Lohse model, while the Pr-dependency is not. The most important finding is that epsilon upsilon,c rather than the thermal dissipation rate, has an exact balance with the directly measured local Nusselt number Nuc in the cell center.
520 $a Our measured acceleration statistics show that its vertical component is generally smaller than the two lateral ones, which is caused by the vorticity of the thermal plumes. It is further found that the acceleration variance in the central region of the system is dominated by contributions from turbulent background, rather than those from the buoyancy force and that the Heisenberg-Yaglom relation holds in that region. From this, we obtain the first experimental results of the constant a0 of the acceleration variance at the micro-scale Reynolds number range 20 ≤ Rlambda ≤ 120 .
520 $a Our study of the reversals of the large scale flow in Rayleigh-Benard convection using both experimental and numerical approaches reveals that the reversal events are triggered by the growth of the corner rolls. Moreover, the Rayleigh vs Prandtl number space for reversal and stable states is mapped out. It is found that the occurrence of reversals sensitively depends on these parameters.
520 $a We use three data sets from different types of turbulent flows, along with the one in our Rayleigh-Benard convection, to study the behavior of the Kolmogorov constants C2, C k, and Ck1 which are, respectively, the coefficients of the second order longitudinal structure function, the three dimensional and one-dimensional longitudinal energy spectra in the inertial range. It is found that their ratios (C2/ Ck1 and Ck/C k1) all exhibit clear dependence on the micro-scale Reynolds number Rlambda, implying that they cannot all be independent of Rlambda. This is in sharp contrast to the generally held belief that these constants are universal with respect to the Reynolds number.
520 $a Lastly, an investigation of thermal convection in nanofluids is carried out. It is found that there is a transition near Ra c &sime; 2.5 x 109 for the global heat transport. For Ra > Rac, the nanofluid can be treated as single phase fluid in this parameter range and the measured Nu of the nanofluid is roughly the same as that of pure water. For Ra < Rac, Nu becomes smaller than that of the water, and the deviation becomes larger with decreasing Ra. The measured instantaneous Nu(t) shows strong and quasi-periodic fluctuations, which is absent when Ra > Rac, suggesting the significant decrease of the nanofluid Nu may be caused by the mass diffusion of nanoparticles.
590 $a School code: 1307.
650 4 $a Physics, Fluid and Plasma. $3 1018402
650 4 $a Energy. $3 876794
690 $a 0759
690 $a 0791
710 2 $a The Chinese University of Hong Kong (Hong Kong). $3 1017547
773 0 $t Dissertation Abstracts International $g 73-08B(E).
790 $a 1307
791 $a Ph.D.
792 $a 2011
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3504742