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.

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.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

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