The Experts below are selected from a list of 153918 Experts worldwide ranked by ideXlab platform
Penger Tong - One of the best experts on this subject based on the ideXlab platform.
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extraction of plumes in turbulent thermal convection
Physical Review Letters, 2004Co-Authors: Emily S C Ching, Penger Tong, Xiaodong Shang, Hong Guo, Keqing XiaAbstract:We present a scheme to extract the Velocity of buoyant structures in turbulent thermal convection from simultaneous Local Velocity and temperature measurements. Applying this scheme to measurements taken at positions within the convection cell where the buoyant structures are dominated by plumes, we obtain the temperature dependence of the plume Velocity and understand our results using the equations of motion. We further obtain the scaling behavior of the average Local heat flux in the vertical direction at the cell center with the Rayleigh number and find that the scaling exponent is different from that measured for the Nusselt number. This difference leads to the conclusion that heat cannot be mainly transported through the central region of the convection cell.
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Velocity oscillations in turbulent rayleigh benard convection
Physics of Fluids, 2004Co-Authors: Xinliang Qiu, Penger Tong, Xiaodong Shang, Keqing XiaAbstract:A systematic study of Velocity oscillations in turbulent thermal convection is carried out in small aspect-ratio cells filled with water. Local Velocity fluctuations and temperature-Velocity cross-correlation functions are measured over varying Rayleigh numbers and spatial positions across the entire convection cell. These structural measurements reveal how the thermal plumes interact with the bulk fluid in a closed cell and provide an interesting physical picture for the dynamics of the temperature and Velocity oscillations in turbulent convection.
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measurements of the instantaneous Velocity difference and the Local Velocity with a fiber optic coupler
Journal of The Optical Society of America A-optics Image Science and Vision, 2001Co-Authors: Shenghong Yao, Penger Tong, Viktor K Horvath, Bruce J Ackerson, Walter I GoldburgAbstract:New optical arrangements with two single-mode input fibers and a fiber-optic coupler are devised to measure the instantaneous Velocity difference and the Local Velocity. The fibers and the coupler are polarization-preserving to guarantee a high signal-to-noise ratio. When the two input fibers are used to collect the scattered light with the same momentum-transfer vector but from two spatially separated regions in a flow, the obtained signals interfere when combined via the fiber-optic coupler. The resultant light received by a photomultiplier tube contains a cross-beat frequency proportional to the Velocity difference between the two measuring points. If the two input fibers are used to collect the scattered light from a common scattering region but with two different momentum-transfer vectors, then the resultant light contains a self-beat frequency proportional to the Local Velocity at the measuring point. The experiment shows that both the cross-beat and the self-beat signals are large and that the standard laser Doppler signal processor can be used to measure the Velocity difference and the Local Velocity in real time. The new technique will have various applications in the general area of fluid dynamics.
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large scale coherent rotation and oscillation in turbulent thermal convection
Physical Review E, 2000Co-Authors: Penger TongAbstract:In this Rapid Communication, we report laser Doppler velocimetry ~LDV! measurements of the Velocity profile in an aspect-ratio-one cell filled with water. LDV measures the Local Velocity as a function of time and the Velocity profile is obtained by scanning the Velocity probe over the whole convection cell. As will be shown below, because of the spatial confinement, the large-scale motion in turbulent convection is stabilized in the closed cell and thus LDV can be used to study its dynamics in great detail. It is found that LDV is capable of measuring the Local Velocity with high accuracy ~better than 1%! over the entire cell, except near the upper and lower thermal boundary layers whose thickness is of the order of 1 mm. In the boundary layer region, fluctuations of the fluid refractive index due to large temperature fluctuations cause the two laser beams used in LDV to wander and defocus in the fluid. This corruption of laser beam properties reduces the signal-to-noise level of LDV.
Daniel Bonn - One of the best experts on this subject based on the ideXlab platform.
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yield stress and shear banding in granular suspensions
Physical Review Letters, 2009Co-Authors: Abdoulaye Fall, Guillaume Ovarlez, Francois Bertrand, Daniel BonnAbstract:We study the emergence of a yield stress in dense suspensions of non-Brownian particles by combining Local Velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear-banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of 62.7±0.3%.
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yield stress and shear banding in granular suspensions
Physical Review Letters, 2009Co-Authors: Guillaume Ovarlez, Abdoulaye Fall, Francois Bertrand, Daniel BonnAbstract:We study the emergence of a yield stress in dense suspensions of non-Brownian particles by combining Local Velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear-banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of $62.7\ifmmode\pm\else\textpm\fi{}0.3%$.
Abdoulaye Fall - One of the best experts on this subject based on the ideXlab platform.
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yield stress and shear banding in granular suspensions
Physical Review Letters, 2009Co-Authors: Abdoulaye Fall, Guillaume Ovarlez, Francois Bertrand, Daniel BonnAbstract:We study the emergence of a yield stress in dense suspensions of non-Brownian particles by combining Local Velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear-banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of 62.7±0.3%.
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yield stress and shear banding in granular suspensions
Physical Review Letters, 2009Co-Authors: Guillaume Ovarlez, Abdoulaye Fall, Francois Bertrand, Daniel BonnAbstract:We study the emergence of a yield stress in dense suspensions of non-Brownian particles by combining Local Velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear-banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of $62.7\ifmmode\pm\else\textpm\fi{}0.3%$.
Keqing Xia - One of the best experts on this subject based on the ideXlab platform.
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extraction of plumes in turbulent thermal convection
Physical Review Letters, 2004Co-Authors: Emily S C Ching, Penger Tong, Xiaodong Shang, Hong Guo, Keqing XiaAbstract:We present a scheme to extract the Velocity of buoyant structures in turbulent thermal convection from simultaneous Local Velocity and temperature measurements. Applying this scheme to measurements taken at positions within the convection cell where the buoyant structures are dominated by plumes, we obtain the temperature dependence of the plume Velocity and understand our results using the equations of motion. We further obtain the scaling behavior of the average Local heat flux in the vertical direction at the cell center with the Rayleigh number and find that the scaling exponent is different from that measured for the Nusselt number. This difference leads to the conclusion that heat cannot be mainly transported through the central region of the convection cell.
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Velocity oscillations in turbulent rayleigh benard convection
Physics of Fluids, 2004Co-Authors: Xinliang Qiu, Penger Tong, Xiaodong Shang, Keqing XiaAbstract:A systematic study of Velocity oscillations in turbulent thermal convection is carried out in small aspect-ratio cells filled with water. Local Velocity fluctuations and temperature-Velocity cross-correlation functions are measured over varying Rayleigh numbers and spatial positions across the entire convection cell. These structural measurements reveal how the thermal plumes interact with the bulk fluid in a closed cell and provide an interesting physical picture for the dynamics of the temperature and Velocity oscillations in turbulent convection.
Xiaodong Shang - One of the best experts on this subject based on the ideXlab platform.
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extraction of plumes in turbulent thermal convection
Physical Review Letters, 2004Co-Authors: Emily S C Ching, Penger Tong, Xiaodong Shang, Hong Guo, Keqing XiaAbstract:We present a scheme to extract the Velocity of buoyant structures in turbulent thermal convection from simultaneous Local Velocity and temperature measurements. Applying this scheme to measurements taken at positions within the convection cell where the buoyant structures are dominated by plumes, we obtain the temperature dependence of the plume Velocity and understand our results using the equations of motion. We further obtain the scaling behavior of the average Local heat flux in the vertical direction at the cell center with the Rayleigh number and find that the scaling exponent is different from that measured for the Nusselt number. This difference leads to the conclusion that heat cannot be mainly transported through the central region of the convection cell.
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Velocity oscillations in turbulent rayleigh benard convection
Physics of Fluids, 2004Co-Authors: Xinliang Qiu, Penger Tong, Xiaodong Shang, Keqing XiaAbstract:A systematic study of Velocity oscillations in turbulent thermal convection is carried out in small aspect-ratio cells filled with water. Local Velocity fluctuations and temperature-Velocity cross-correlation functions are measured over varying Rayleigh numbers and spatial positions across the entire convection cell. These structural measurements reveal how the thermal plumes interact with the bulk fluid in a closed cell and provide an interesting physical picture for the dynamics of the temperature and Velocity oscillations in turbulent convection.
