On the Anisotropic Vorticity in Turbulent Channel Flows

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Helge I. Andersson ◽  
Lihao Zhao ◽  
Evan A. Variano
Keyword(s):  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Channel Flows ◽  
Vorticity Field ◽  
Particle Suspensions ◽  
Low Reynolds Numbers ◽  
Turbulent Channel Flows ◽  
Low Reynolds

Revisiting the fluctuating vorticity field in the centerplane of a turbulent channel flow, we show that the vorticity is distinctly anisotropic at low Reynolds numbers (Re). This result is in contrast with some earlier conclusions. The anisotropy is a function of Re, and we have compiled data to show that the anisotropy gradually vanishes with increasing Re. Acknowledging the anisotropy is important for current efforts on simulating turbulent particle suspensions.

Low-Reynolds-number effects in a fully developed turbulent channel flow

1992 ◽  
Vol 236 ◽  
pp. 579-605 ◽  
Author(s):  
R. A. Antonia ◽  
M. Teitel ◽  
J. Kim ◽  
L. W. B. Browne
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Low Reynolds Number ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Wall Region ◽  
Low Reynolds Numbers ◽  
Reynolds Number Effects ◽  
Low Reynolds ◽  
Inner Region

Low-Reynolds-number effects are observed in the inner region of a fully developed turbulent channel flow, using data obtained either from experiments or by direct numerical simulations. The Reynolds-number influence is observed on the turbulence intensities and to a lesser degree on the average production and dissipation of the turbulent energy. In the near-wall region, the data confirm Wei & Willmarth's (1989) conclusion that the Reynolds stresses do not scale on wall variables. One of the reasons proposed by these authors to account for this behaviour, namely the ‘geometry’ effect or direct interaction between inner regions on opposite walls, was investigated in some detail by introducing temperature at one of the walls, both in experiment and simulation. Although the extent of penetration of thermal excursions into the opposite side of the channel can be significant at low Reynolds numbers, the contribution these excursions make to the Reynolds shear stress and the spanwise vorticity in the opposite wall region is negligible. In the inner region, spectra and co-spectra of the velocity fluctuations u and v change rapidly with the Reynolds number, the variations being mainly confined to low wavenumbers in the u spectrum. These spectra, and the corresponding variances, are discussed in the context of the active/inactive motion concept and the possibility of increased vortex stretching at the wall. A comparison is made between the channel and the boundary layer at low Reynolds numbers.

scholarly journals Kinematics and Dynamics of Turbulent Bands at Low Reynolds Numbers in Channel Flow

Entropy ◽  
2020 ◽  
Vol 22 (10) ◽  
pp. 1167 ◽  
Author(s):  
Xiangkai Xiao ◽  
Baofang Song
Keyword(s):  
Channel Flow ◽  
Tilt Angle ◽  
Propagation Speed ◽  
Reynolds Numbers ◽  
Point Of View ◽  
Kinematics And Dynamics ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Low Speed Streaks ◽  
Large Flow

Channel flow turbulence exhibits interesting spatiotemporal complexities at transitional Reynolds numbers. In this paper, we investigated some aspects of the kinematics and dynamics of fully localized turbulent bands in large flow domains. We discussed the recent advancement in the understanding of the wave-generation at the downstream end of fully localized bands. Based on the discussion, we proposed a possible mechanism for the tilt direction selection. We measured the propagation speed of the downstream end and the advection speed of the low-speed streaks in the bulk of turbulent bands at various Reynolds numbers. Instead of measuring the tilt angle by treating an entire band as a tilted object as in prior studies, we proposed that, from the point of view of the formation and growth of turbulent bands, the tilt angle should be determined by the relative speed between the downstream end and the streaks in the bulk. We obtained a good agreement between our calculation of the tilt angle and the reported results in the literature at relatively low Reynolds numbers.

Characteristics of Coherent Structures in Channel Flows During Low Reynolds Number Mixed Convection

2014 ◽  
Author(s):  
Ahmed Elatar ◽  
Kamran Siddiqui
Keyword(s):  
Mixed Convection ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Channel Flows ◽  
Heated Wall ◽  
Low Reynolds Numbers ◽  
Square Channel ◽  
Low Reynolds

Characteristics of coherent structures generated in channel flows during low Reynolds numbers mixed convection have been investigated in a square channel. The Gr/Re2 ranged between 21 and 206 which indicates that natural convection was dominant over forced convection. Two-dimensional velocity fields were measured using particle image velocimetry (PIV) technique in different planes to obtain a three-dimensional perspective of the flow field in the channel. The coherent structures were detected from the turbulent velocity fields using an algorithm based on the velocity gradient tensor second invariant (Q). The location of each detected coherent structure was recorded and its turbulent kinetic energy was computed. It was found that the strength of coherent structures increased with an increase in the bottom wall temperature. The results also indicate that the coherent structures present in the region away from the bottom heated wall were more energetic compared to the coherent structures present within the thermal boundary layer.

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