Higher Order Moments in the Entrainment Zone of Turbulent Penetrative Thermal Convection

1986 ◽  
Vol 108 (2) ◽  
pp. 323-329 ◽  
Author(s):  
R. Kumar ◽  
R. J. Adrian
Keyword(s):  
Heat Flux ◽  
Inversion Layer ◽  
Interfacial Region ◽  
Interfacial Zone ◽  
Stable Layer ◽  
Third Order ◽  
Beam Laser ◽  
Dual Beam ◽  
Entrainment Zone ◽  
Instantaneous Values

In a simulation of the lifting of an atmospheric inversion layer in the laboratory, measurements have been made to understand the dynamics in the interfacial region capped by a stable, linearly stratified layer. Instantaneous values of vertical and horizontal components of velocity have been measured using a two-component dual-beam laser Doppler anemometer. Temperature fluctuations have been made simultaneously. Detailed measurements of all relevant horizontally averaged one-point moments including heat flux and third-order joint vertical velocity–temperature moments have been obtained. The negative heat flux region is well defined in the entrainment zone, and varies in thickness with different stable layer temperature gradients. The entrainment mechanism is probably most important only in the top part of the interfacial zone. The present data supplement data obtained in the atmosphere, and they compare favorably with the existing data in the literature.

Temperature and Stress Analysis of Dual-Beam Laser Cladding on Gray Cast Iron Surface

Applied laser ◽  
2014 ◽  
Vol 34 (4) ◽  
pp. 288-293
Author(s):  
刘衍聪 Liu Yancong ◽  
范常峰 Fan Changfeng ◽  
尹晓丽 Yin Xiaoli ◽  
杨光辉 Yang Guanghui ◽  
许鹏云 Xu Pengyun
Keyword(s):  
Cast Iron ◽  
Stress Analysis ◽  
Laser Cladding ◽  
Gray Cast Iron ◽  
Iron Surface ◽  
Gray Cast ◽  
Beam Laser ◽  
Dual Beam

Effect of Energy Ratio on Dual Beam Laser Welding Characteristics

2017 ◽  
Vol 44 (3) ◽  
pp. 0302003
Author(s):  
马国龙 Ma Guolong ◽  
李俐群 Li Liqun ◽  
陈彦宾 Chen Yanbin
Keyword(s):  
Laser Welding ◽  
Energy Ratio ◽  
Beam Laser ◽  
Dual Beam

Influence of Temperature Distribution of Ceramic Coating Using Top-Hat Assistant Laser Beam in Dual-Beam Laser Cladding

2014 ◽  
Vol 41 (7) ◽  
pp. 0703012
Author(s):  
吴东江 Wu Dongjiang ◽  
褚洋 Chu Yang ◽  
牛方勇 Niu Fangyong ◽  
马广义 Ma Guangyi ◽  
庄娟 Zhuang Juan
Keyword(s):  
Temperature Distribution ◽  
Laser Beam ◽  
Laser Cladding ◽  
Ceramic Coating ◽  
Influence Of Temperature ◽  
Beam Laser ◽  
Dual Beam

Investigation of Fluid Flow and Heat Transfer in 3D Dual-Beam Laser Keyhole Welding

2010 ◽  
Author(s):  
Jun Zhou ◽  
Hai-Lung Tsai
Keyword(s):  
Heat Transfer ◽  
Laser Welding ◽  
Welding Process ◽  
Solidification Process ◽  
Melt Flow ◽  
Single Beam ◽  
Keyhole Welding ◽  
Beam Laser ◽  
Dual Beam ◽  
Laser Keyhole Welding

Dual-beam laser welding has become an emerging joining technique. Studies have demonstrated that it can provide benefits over conventional single-beam laser welding, such as increasing keyhole stability, slowing down cooling rate and delaying the humping onset to a higher welding speed. It is also reported to be able to improve weld quality significantly. However, due to its complexity the development of this promising technique has been limited to the trial-and-error procedure. In this study, mathematical models are developed to investigate the heat transfer, melt flow, and solidification process in three-dimensional dual-beam laser keyhole welding. Effects of key parameters, such as laser-beam configuration on melt flow, weld shape, and keyhole dynamics are studied. Some experimentally observed phenomena, such as the changes of the weld pool shape from oval to circle and from circle to oval during the welding process are analyzed in current study.

scholarly journals Penetration of boundary-driven flows into a rotating spherical thermally stratified fluid

2019 ◽  
Vol 864 ◽  
pp. 519-553 ◽  
Author(s):  
Grace A. Cox ◽  
Christopher J. Davies ◽  
Philip W. Livermore ◽  
James Singleton
Keyword(s):  
Heat Flux ◽  
Outer Boundary ◽  
Relative Size ◽  
Stratified Fluid ◽  
Temperature Gradients ◽  
Heterogeneous Structure ◽  
Stable Layer ◽  
Dimensionless Numbers ◽  
Thermal Anomalies ◽  
The Core

Motivated by the dynamics within terrestrial bodies, we consider a rotating, strongly thermally stratified fluid within a spherical shell subject to a prescribed laterally inhomogeneous heat-flux condition at the outer boundary. Using a numerical model, we explore a broad range of three key dimensionless numbers: a thermal stratification parameter (the relative size of boundary temperature gradients to imposed vertical temperature gradients), $10^{-3}\leqslant S\leqslant 10^{4}$, a buoyancy parameter (the strength of applied boundary heat-flux anomalies), $10^{-2}\leqslant B\leqslant 10^{6}$, and the Ekman number (ratio of viscous to Coriolis forces), $10^{-6}\leqslant E\leqslant 10^{-4}$. We find both steady and time-dependent solutions and delineate the regime boundaries. We focus on steady-state solutions, for which a clear transition is found between a low $S$ regime, in which buoyancy dominates the dynamics, and a high $S$ regime, in which stratification dominates. For the low-$S$ regime, we find that the characteristic flow speed scales as $B^{2/3}$, whereas for high-$S$, the radial and horizontal velocities scale respectively as $u_{r}\sim S^{-1}$, $u_{h}\sim S^{-3/4}B^{1/4}$ and are confined within a thin layer of depth $(SB)^{-1/4}$ at the outer edge of the domain. For the Earth, if lower mantle heterogeneous structure is due principally to chemical anomalies, we estimate that the core is in the high-$S$ regime and steady flows arising from strong outer boundary thermal anomalies cannot penetrate the stable layer. However, if the mantle heterogeneities are due to thermal anomalies and the heat-flux variation is large, the core will be in a low-$S$ regime in which the stable layer is likely penetrated by boundary-driven flows.

scholarly journals Resolution Dependence of Turbulent Structures in Convective Boundary Layer Simulations

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 986 ◽  
Author(s):  
Mary-Jane M. Bopape ◽  
Robert S. Plant ◽  
Omduth Coceal
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Convective Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Quadrant Analysis ◽  
Turbulent Structures ◽  
Convective Boundary ◽  
Large Eddy ◽  
Lower Boundary Layer

Large-eddy simulations are performed using the U.K. Met Office Large Eddy Model to study the effects of resolution on turbulent structures in a convective boundary layer. A standard Smagorinsky subgrid scheme is used. As the grid length is increased, the diagnosed height of the boundary layer increases, and the horizontally- and temporally-averaged temperature near the surface and in the inversion layer increase. At the highest resolution, quadrant analysis shows that the majority of events in the lower boundary layer are associated with cold descending air, followed by warm ascending air. The largest contribution to the total heat flux is made by warm ascending air, with associated strong thermals. At lower resolutions, the contribution to the heat flux from cold descending air is increased, and that from cold ascending air is reduced in the lower boundary layer; around the inversion layer, however, the contribution from cold ascending air is increased. Calculations of the heating rate show that the differences in cold ascending air are responsible for the warm bias below the boundary layer top in the low resolution simulations. Correlation length and time scales for coherent resolved structures increase with increasing grid coarseness. The results overall suggest that differences in the simulations are due to weaker mixing between thermals and their environment at lower resolutions. Some simple numerical experiments are performed to increase the mixing in the lower resolution simulations and to investigate backscatter. Such simulations are successful at reducing the contribution of cold ascending air to the heat flux just below the inversion, although the effects in the lower boundary layer are weaker.

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