Alignment of slender fibers and thin disks induced by coherent structures of wall turbulence

2021 ◽  
pp. 103837
Author(s):  
Zhiwen Cui ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu ◽  
Helge I. Andersson ◽  
Lihao Zhao
Keyword(s):  
Coherent Structures ◽  
Wall Turbulence ◽  
Thin Disks

scholarly journals Transfer, Segregation and Deposition of Heavy Particles in Horizontal and Vertical Turbulent Channel Flows

2003 ◽  
Author(s):  
Cristian Marchioli ◽  
Fabio Sbrizzai ◽  
Alfredo Soldati
Keyword(s):  
Coherent Structures ◽  
Particle Distribution ◽  
Outer Region ◽  
Turbulent Channel Flow ◽  
Transfer Mechanism ◽  
Wall Turbulence ◽  
Wall Region ◽  
Turbulence Structure ◽  
Low Speed ◽  
Low Speed Streaks

Particle transfer in the wall region of turbulent boundary layers is dominated by the coherent structures which control the turbulence regeneration cycle. Coherent structures bring particles toward the wall and away from the wall and favour particle segregation in the viscous region giving rise to nonuniform particle distribution profiles which peak close to the wall. In this work, we focus on the transfer mechanism of different size particles and on the influence of gravity on particles deposition. By tracking O(105) particles in Direct Numerical Simulation (DNS) of a turbulent channel flow at Reτ = 150, we find that particles may reach the wall directly or may accumulate in the wall region, under the low-speed streaks. Even though low-speed streaks are ejection-like environments, particles are not re-entrained into the outer region. Particles segregated very near the wall by the trapping mechanisms we investigated in a previous work [1] are slowly driven to the wall. We find that gravity plays a role on particle distribution but, for small particles (τp+ < 3), the controlling transfer mechanism is related to near-wall turbulence structure.

scholarly journals Three-Dimensional Visualization of the Quasi-Coherent Structures in Numerically Simulated Wall Turbulence

1991 ◽  
Vol 11 (Supplement1) ◽  
pp. 29-32
Author(s):  
Keiji KOBAYASHI ◽  
Nobuhide KASAGI ◽  
Akiyoshi KURODA ◽  
Yasuoki TOMITA
Keyword(s):  
Coherent Structures ◽  
Three Dimensional ◽  
Wall Turbulence

Active Control of Near-Wall Coherent Structures

2002 ◽  
Author(s):  
P. Konieczny ◽  
A. Bottaro ◽  
V. Monturet ◽  
B. Nogarede
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Coherent Structures ◽  
Large Scale ◽  
Travelling Wave ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Integral Control ◽  
Macroscopic Simulation ◽  
Near Wall

This work aims at finding efficient means to reduce skin friction drag in a turbulent boundary layer. The argument on which the study is based is that turbulence exists near a wall because of the presence of an autonomous cycle which is maintained even in the absence of forcing from the free-stream. The central elements of this cycle are the near-wall coherent structures whose dynamics control the turbulence production. It is postulated that an action at the wall capable of disrupting the turbulent wall-cycle can yield a significant skin friction reduction. A model cycle is produced by embedding artificial, large scale streamwise vortices and streaks in a Blasius boundary layer. A control is then conceived, meant to produce an agglomeration of the streaks to hamper the cycle. The action envisaged consists in a movement of the wall, in the form of a spanwise standing or travelling wave of sufficiently long wavelength. The controllers in the present macroscopic simulation are simply cantilever beams whose movement is driven by ceramic piezo-actuators. Piezoelectric fibers realizing the same action (properly rescaled) provide, possibly, the answer to the technological challenge of the integral control of near-wall turbulence.

Coherent structures in wall turbulence and mechanism for drag reduction control

2013 ◽  
Vol 56 (6) ◽  
pp. 1053-1061 ◽  
Author(s):  
ChunXiao Xu ◽  
BingQing Deng ◽  
WeiXi Huang ◽  
GuiXiang Cui
Keyword(s):  
Drag Reduction ◽  
Coherent Structures ◽  
Wall Turbulence

Influence of the Reynolds number on the vortical structures in the logarithmic region of turbulent boundary layers

2013 ◽  
Vol 716 ◽  
pp. 5-50 ◽  
Author(s):  
Sophie Herpin ◽  
Michel Stanislas ◽  
Jean Marc Foucaut ◽  
Sebastien Coudert
Keyword(s):  
Reynolds Number ◽  
Coherent Structures ◽  
Flow Region ◽  
Wall Turbulence ◽  
Statistical Characteristics ◽  
Present Contribution ◽  
Vortical Structures ◽  
Stereo Particle Image Velocimetry ◽  
Logarithmic Region ◽  
The Subject

AbstractNear-wall turbulence is a subject of prime importance for turbulence modelling. Coherent structures were hypothesized early by Theodorsen in this flow region and have been the subject of intensive research ever since. The overall organization of these coherent structures has now been well assessed. Vortical structures appear to play a key role in this organization. Their characteristics and scaling have been studied by many authors as listed in the Introduction. The present contribution to the subject relies on high-resolution stereo particle image velocimetry (PIV) to study these structures. High-quality measurements are performed in a thick turbulent boundary layer at different values of the Reynolds number. The data quality is first assessed by comparing the statistics to those of hot-wire anemometry and direct numerical simulation data. The agreement between the two appears satisfactory. The PIV data are then processed in order to extract the vortex characteristics in a streamwise plane and in a spanwise plane. The statistical characteristics of these vortices are analysed in detail as a function of wall distance. The scaling of the data appears to be universal when the Kolmogorov scales are used. These results are analysed and discussed in terms of their probability density functions. This leads to a question regarding the Kolmogorov cascade in this region of the flow.

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