The Experts below are selected from a list of 3489 Experts worldwide ranked by ideXlab platform
Christian Trägådh - One of the best experts on this subject based on the ideXlab platform.
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u′v′ Reynolds stress in the Viscous Sublayer over a wide range of Re numbers
AIChE Journal, 1994Co-Authors: Christer Rosén, Christian TrägådhAbstract:To test the ability of different turbulence models to predict the turbulent momentum transport in the Viscous Sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: −u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-ϵ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-ϵ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the Viscous Sublayer.
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u v reynolds stress in the Viscous Sublayer over a wide range of re numbers
Aiche Journal, 1994Co-Authors: Christer Rosén, Christian TrägådhAbstract:To test the ability of different turbulence models to predict the turbulent momentum transport in the Viscous Sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: −u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-ϵ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-ϵ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the Viscous Sublayer.
Igor Vigdorovich - One of the best experts on this subject based on the ideXlab platform.
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A law of the wall for turbulent boundary layers with suction: Stevenson’s formula revisited
Physics of Fluids, 2016Co-Authors: Igor VigdorovichAbstract:The turbulent velocity field in the Viscous Sublayer of the boundary layer with suction to a first approximation is homogeneous in any direction parallel to the wall and is determined by only three constant quantities — the wall shear stress, the suction velocity, and the fluid viscosity. This means that there exists a finite algebraic relation between the turbulent shear stress and the longitudinal mean-velocity gradient, using which as a closure condition for the equations of motion, we establish an exact asymptotic behavior of the velocity profile at the outer edge of the Viscous Sublayer. The obtained relationship provides a generalization of the logarithmic law to the case of wall suction.
Christer Rosén - One of the best experts on this subject based on the ideXlab platform.
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u′v′ Reynolds stress in the Viscous Sublayer over a wide range of Re numbers
AIChE Journal, 1994Co-Authors: Christer Rosén, Christian TrägådhAbstract:To test the ability of different turbulence models to predict the turbulent momentum transport in the Viscous Sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: −u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-ϵ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-ϵ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the Viscous Sublayer.
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u v reynolds stress in the Viscous Sublayer over a wide range of re numbers
Aiche Journal, 1994Co-Authors: Christer Rosén, Christian TrägådhAbstract:To test the ability of different turbulence models to predict the turbulent momentum transport in the Viscous Sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: −u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-ϵ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-ϵ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the Viscous Sublayer.
John Kim - One of the best experts on this subject based on the ideXlab platform.
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Control of the Viscous Sublayer for drag reduction
Physics of Fluids, 2002Co-Authors: Changhoon Lee, John KimAbstract:We investigate the possibility of manipulating turbulence structures in the Viscous Sublayer for the purpose of drag reduction using a direct numerical simulation of a turbulent channel flow. Recognizing that a great portion of production of vorticity occurs in the Viscous Sublayer, a body force is used to suppress spanwise velocity in the Sublayer, and a significant amount of drag reduction is obtained. A more realistic body force or wall movement in the spanwise direction using instantaneous wall-shear stress in a closed-loop control is shown to reduce drag as much as 35%. Implementation of such a body force using an electromagnetic force is also discussed.
Myung Kyoon Chung - One of the best experts on this subject based on the ideXlab platform.
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Revisit of Viscous Sublayer scaling law
Physics of Fluids, 2004Co-Authors: Ju Yeop Park, Myung Kyoon ChungAbstract:Recent study has shown that the valid region of linear velocity profile in the Viscous Sublayer of turbulent channel flow is only the asymptotic limit y+→0 even at a very high Reynolds number. In the view of similarity, this result implies that the conventional complete similarity assumption, which is the basis of linear velocity profile, is not valid. In terms of extended similarity argument of G. I. Barenblatt [J. Eng. Math. 36, 361 (1999)], it is shown that the plausible similarity assumption for the Viscous Sublayer is the incomplete similarity in y+ and the complete similarity in h+(=huτ/ν), where h is channel half width. The resulting velocity profile based on these assumptions has a quartic term of y+ from Reynolds stress in addition to a linear term of y+ from Viscous stress, which greatly enlarges the extent of valid region of similarity.
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Application of Lumley's drag reduction model to two-phase gas-particle flow in a pipe
Journal of Fluids Engineering-transactions of The Asme, 1991Co-Authors: Myung Kyoon Chung, Hyung Jin SungAbstract:This paper discusses two-fluid model incorporated with Lumley's drag reduction model to analyze the mechanism of momentum transfer in the turbulent dilute gas-particle flow in a vertical pipe. The change of the effective Viscous Sublayer thickness by the presence of particles is modeled by Lumley's theoretical model. The numerical computations of the friction factor and the pressure drop in a fully developed pipe flow are in good agreement with the corresponding experimental data for an average particle size of 15 {mu}m. it is proved that Lumley's model is successful in predicting the correct reduction behavior of the drag in the gas-particle flows It has been confirmed that the effective Viscous Sublayer thickness for two-phase gas-particle flow is dependent on the particle relaxation time, Kolmogoroff time scale and the solids-gas loading ratio.
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Analysis of heat transfer in a pipe carrying two-phase gas-particle suspension
International Journal of Heat and Mass Transfer, 1991Co-Authors: Kee Soo Han, Hyung Jin Sung, Myung Kyoon ChungAbstract:Abstract A ‘two-fluid model’ using the thermal eddy diffusivity concept and Lumley's drag reduction theory, is proposed to analyse heat transfer of the turbulent dilute gas-particle flow in a vertical pipe with constant wall heat flux. The thermal eddy diffusivity model is derived to be a function of the ratio of the heat capacity-density products \ grC p of the gaseous phase and the particulate phase and also of the ratio of the thermal relaxation time scale to that of turbulence. Lumley's theory is applied to find the variation of the Viscous Sublayer thickness depending on the particle loading ratio Z and the relative particle size dp/D. At low loading ratio, the size of the Viscous Sublayer thickness is important for suspension heat transfer, while at higher loading, the effect of the ratio \ gr P C p P / \ gr f C pf . is dominant. The major cause of decrease in the suspension Nusselt number at low loading ratio is found to be due to the increase of the Viscous Sublayer thickness caused by the suppression of turbulence near the wall by the presence of solid particles. Predicted Nusselt numbers using the present model are in satisfactory agreement with available experimental data both in the pipe entrance and the fully developed regions.
