Optimal disturbances in the near-wall region of turbulent channel flows

2016 ◽  
Vol 1 (7) ◽  
Author(s):  
Euiyoung Kim ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Channel Flows ◽  
Wall Region ◽  
Turbulent Channel Flows ◽  
Optimal Disturbances ◽  
Near Wall

Reynolds number effects in the near-wall region of turbulent channel flows

2001 ◽  
Vol 13 (6) ◽  
pp. 1755-1767 ◽  
Author(s):  
M. Fischer ◽  
J. Jovanović ◽  
F. Durst
Keyword(s):  
Reynolds Number ◽  
Channel Flows ◽  
Wall Region ◽  
Turbulent Channel Flows ◽  
Reynolds Number Effects ◽  
Near Wall

On the near-wall structures and statistics of fluctuating pressure in compressible turbulent channel flows

2020 ◽  
Vol 32 (11) ◽  
pp. 115121 ◽  
Author(s):  
Jiupeng Tang ◽  
Zhiye Zhao ◽  
Zhen-Hua Wan ◽  
Nan-Sheng Liu
Keyword(s):  
Channel Flows ◽  
Fluctuating Pressure ◽  
Turbulent Channel Flows ◽  
Wall Structures ◽  
Near Wall

Interactions of Flow Structure With Nano- and Micro-Particles in Turbulent Channel Flows

2018 ◽  
Author(s):  
Amir A. Mofakham ◽  
Goodarz Ahmadi ◽  
John McLaughlin
Keyword(s):  
Relaxation Time ◽  
Coherent Structures ◽  
Concentration Distribution ◽  
Channel Flows ◽  
Small Scale ◽  
Turbulence Structure ◽  
Micro Particles ◽  
Turbulent Channel Flows ◽  
Wide Range ◽  
Near Wall

This study is concerned with the effects of the flow structures including the near-wall coherent eddies in turbulent channel flows on the dispersion and deposition of nano- and micro-particles. A pseudo-spectral computational code was used for direct numerical simulations (DNS) of the Navier-Stokes equations and the corresponding time histories of the instantaneous fluid velocities were evaluated. Under the oneway coupling assumption, the trajectories of a wide range of particle sizes from 10 nm to 80 μm with dimensionless relaxation time of 2.2e−6 to 142 were obtained by solving the particle equation of motion including Stokes drag and Brownian excitations. Dispersion and deposition of particles in the turbulent flow were evaluated and the effects of turbulence structure on different size particles were studied. The simulation results showed that the concentration distribution of small particles that behave like fluid tracer particles were quite random. However, the preferential concentrations appeared as the dimensionless relaxation time increased to 2–20. In particular, the influence of coherent structures in the near-wall regions was clearly detectable on the concentration distribution of particles, as well as, in their deposition pattern. For τ+ = 20 particles due to the increase of relaxation time and inertia of particles, the small-scale turbulent features were filtered out and only the effect of large-scale turbulent eddies could be identified. For τ+ = 2–20 particles, the ensemble/time average of the position of the deposited particles showed specific spacing which was comparable to the size of the near-wall coherent structures.

An improved near-wall treatment for turbulent channel flows

2011 ◽  
Vol 25 (1) ◽  
pp. 41-46 ◽  
Author(s):  
Najla El Gharbi ◽  
Rafik Absi ◽  
Ahmed Benzaoui ◽  
Rachid Bennacer
Keyword(s):  
Channel Flows ◽  
Turbulent Channel Flows ◽  
Near Wall

scholarly journals Spectral analysis of the budget equation in turbulent channel flows at high Reynolds number

2018 ◽  
Vol 860 ◽  
pp. 886-938 ◽  
Author(s):  
Myoungkyu Lee ◽  
Robert D. Moser
Keyword(s):  
Reynolds Number ◽  
Outer Layer ◽  
Large Scale ◽  
Turbulent Energy ◽  
Channel Flows ◽  
Small Scale ◽  
Wall Region ◽  
Transfer Energy ◽  
Energy Flows ◽  
Near Wall

The transport equations for the variances of the velocity components are investigated using data from direct numerical simulations of incompressible channel flows at friction Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$) up to$Re_{\unicode[STIX]{x1D70F}}=5200$. Each term in the transport equation has been spectrally decomposed to expose the contribution of turbulence at different length scales to the processes governing the flow of energy in the wall-normal direction, in scale and among components. The outer-layer turbulence is dominated by very large-scale streamwise elongated modes, which are consistent with the very large-scale motions (VLSM) that have been observed by many others. The presence of these VLSMs drives many of the characteristics of the turbulent energy flows. Away from the wall, production occurs primarily in these large-scale streamwise-elongated modes in the streamwise velocity, but dissipation occurs nearly isotropically in both velocity components and scale. For this to happen, the energy is transferred from the streamwise-elongated modes to modes with a range of orientations through nonlinear interactions, and then transferred to other velocity components. This allows energy to be transferred more-or-less isotropically from these large scales to the small scales at which dissipation occurs. The VLSMs also transfer energy to the wall region, resulting in a modulation of the autonomous near-wall dynamics and the observed Reynolds number dependence of the near-wall velocity variances. The near-wall energy flows are more complex, but are consistent with the well-known autonomous near-wall dynamics that gives rise to streaks and streamwise vortices. Through the overlap region between outer- and inner-layer turbulence, there is a self-similar structure to the energy flows. The VLSM production occurs at spanwise scales that grow with$y$. There is transport of energy away from the wall over a range of scales that grows with$y$. Moreover, there is transfer of energy to small dissipative scales which grows like$y^{1/4}$, as expected from Kolmogorov scaling. Finally, the small-scale near-wall processes characterised by wavelengths less than 1000 wall units are largely Reynolds number independent, while the larger-scale outer-layer processes are strongly Reynolds number dependent. The interaction between them appears to be relatively simple.

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