Subgrid‐scale energy transfer in the near‐wall region of turbulent flows

1994 ◽  
Vol 6 (9) ◽  
pp. 3130-3143 ◽  
Author(s):  
Carlos Härtel ◽  
Leonhard Kleiser ◽  
Friedemann Unger ◽  
Rainer Friedrich
Keyword(s):  
Energy Transfer ◽  
Turbulent Flows ◽  
Wall Region ◽  
Subgrid Scale ◽  
Near Wall

Turbulent Mass Transfer Simulations of Binary Electrolyte in Parallel-Plate Electrode Channel

2012 ◽  
Vol 550-553 ◽  
pp. 2014-2018
Author(s):  
Xiao Lan Zhou ◽  
Cai Xi Liu ◽  
Yu Hong Dong
Keyword(s):  
Mass Transfer ◽  
Turbulent Flows ◽  
Primary Objective ◽  
Wall Turbulence ◽  
Limiting Current ◽  
Solid Boundary ◽  
Wall Region ◽  
Schmidt Numbers ◽  
Near Wall ◽  
Turbulent Mass Transfer

Electrochemical mass transfer in turbulent flows and binary electrolytes is investigated. The primary objective is to provide information about mass transfer in the near-wall region between a solid boundary and a turbulent fluid flow at different Schmidt numbers. Based on the computational fluid dynamics and electrochemistry theories, a model for turbulent electrodes channel flow is established. The turbulent mass transfer in electrolytic processes has been predicted by the direct numerical simulation method under limiting current and galvanostatic conditions, we investigate mean concentration and the structure of the concentration fluctuating filed for different Schmidt numbers from 0.1 to 100 .The effect of different concentration boundary conditions at the electrodes on the near-wall turbulence statistics is also discussed.

Wall accumulation and spatial localization in particle-laden wall flows

2012 ◽  
Vol 699 ◽  
pp. 50-78 ◽  
Author(s):  
G. Sardina ◽  
P. Schlatter ◽  
L. Brandt ◽  
F. Picano ◽  
C. M. Casciola
Keyword(s):  
Turbulent Flows ◽  
Pair Correlation ◽  
Turbulent Channel Flow ◽  
Wall Turbulence ◽  
Small Scale ◽  
Wall Region ◽  
Inertial Particles ◽  
Wall Flows ◽  
Domain Truncation ◽  
Near Wall

AbstractWe study the two main phenomenologies associated with the transport of inertial particles in turbulent flows, turbophoresis and small-scale clustering. Turbophoresis describes the turbulence-induced wall accumulation of particles dispersed in wall turbulence, while small-scale clustering is a form of local segregation that affects the particle distribution in the presence of fine-scale turbulence. Despite the fact that the two aspects are usually addressed separately, this paper shows that they occur simultaneously in wall-bounded flows, where they represent different aspects of the same process. We study these phenomena by post-processing data from a direct numerical simulation of turbulent channel flow with different populations of inertial particles. It is shown that artificial domain truncation can easily alter the mean particle concentration profile, unless the domain is large enough to exclude possible correlation of the turbulence and the near-wall particle aggregates. The data show a strong link between accumulation level and clustering intensity in the near-wall region. At statistical steady state, most accumulating particles aggregate in strongly directional and almost filamentary structures, as found by considering suitable two-point observables able to extract clustering intensity and anisotropy. The analysis provides quantitative indications of the wall-segregation process as a function of the particle inertia. It is shown that, although the most wall-accumulating particles are too heavy to segregate in homogeneous turbulence, they exhibit the most intense local small-scale clustering near the wall as measured by the singularity exponent of the particle pair correlation function.

scholarly journals Turbulent boundary layers over permeable walls: scaling and near-wall structure

2011 ◽  
Vol 687 ◽  
pp. 141-170 ◽  
Author(s):  
C. Manes ◽  
D. Poggi ◽  
L. Ridolfi
Keyword(s):  
Turbulent Flows ◽  
Laser Doppler Anemometry ◽  
Wall Turbulence ◽  
Shear Instability ◽  
Wall Structure ◽  
Wall Region ◽  
Mean Velocity ◽  
Wide Range ◽  
Permeable Walls ◽  
Near Wall

AbstractThis paper presents an experimental study devoted to investigating the effects of permeability on wall turbulence. Velocity measurements were performed by means of laser Doppler anemometry in open channel flows over walls characterized by a wide range of permeability. Previous studies proposed that the von Kármán coefficient associated with mean velocity profiles over permeable walls is significantly lower than the standard values reported for flows over smooth and rough walls. Furthermore, it was observed that turbulent flows over permeable walls do not fully respect the widely accepted paradigm of outer-layer similarity. Our data suggest that both anomalies can be explained as an effect of poor inner–outer scale separation if the depth of shear penetration within the permeable wall is considered as the representative length scale of the inner layer. We observed that with increasing permeability, the near-wall structure progressively evolves towards a more organized state until it reaches the condition of a perturbed mixing layer where the shear instability of the inflectional mean velocity profile dictates the scale of the dominant eddies. In our experiments such shear instability eddies were detected only over the wall with the highest permeability. In contrast attached eddies were present over all the other wall conditions. On the basis of these findings, we argue that the near-wall structure of turbulent flows over permeable walls is regulated by a competing mechanism between attached and shear instability eddies. We also argue that the ratio between the shear penetration depth and the boundary layer thickness quantifies the ratio between such eddy scales and, therefore, can be used as a diagnostic parameter to assess which eddy structure dominates the near-wall region for different wall permeability and flow conditions.

Regeneration mechanisms of near-wall turbulence structures

1995 ◽  
Vol 287 ◽  
pp. 317-348 ◽  
Author(s):  
James M. Hamilton ◽  
John Kim ◽  
Fabian Waleffe
Keyword(s):  
Turbulent Flows ◽  
Wall Turbulence ◽  
Direct Result ◽  
Wall Region ◽  
Computational Domain ◽  
Streamwise Vortices ◽  
Turbulence Structures ◽  
Wall Structures ◽  
Fully Developed Turbulent Flow ◽  
Near Wall

Direct numerical simulations of a highly constrained plane Couette flow are employed to study the dynamics of the structures found in the near-wall region of turbulent flows. Starting from a fully developed turbulent flow, the dimensions of the computational domain are reduced to near the minimum values which will sustain turbulence. A remarkably well-defined, quasi-cyclic and spatially organized process of regeneration of near-wall structures is observed. This process is composed of three distinct phases: formation of streaks by streamwise vortices, breakdown of the streaks, and regeneration of the streamwise vortices. Each phase sets the stage for the next, and these processes are analysed in detail. The most novel results concern vortex regeneration, which is found to be a direct result of the breakdown of streaks that were originally formed by the vortices, and particular emphasis is placed on this process. The spanwise width of the computational domain corresponds closely to the typically observed spanwise spacing of near-wall streaks. When the width of the domain is further reduced, turbulence is no longer sustained. It is suggested that the observed spacing arises because the time scales of streak formation, breakdown and vortex regeneration become mismatched when the streak spacing is too small, and the regeneration cycle at that scale is broken.

Some insights for the prediction of near-wall turbulence

2013 ◽  
Vol 723 ◽  
pp. 126-139 ◽  
Author(s):  
Farid Karimpour ◽  
Subhas K. Venayagamoorthy
Keyword(s):  
Turbulent Flows ◽  
Time Scales ◽  
Time Scale ◽  
Eddy Viscosity ◽  
Wall Turbulence ◽  
Wall Region ◽  
Velocity Scale ◽  
The Mean ◽  
Near Wall Turbulence ◽  
Near Wall

AbstractIn this paper, we revisit the eddy viscosity formulation to highlight a number of important issues that have direct implications for the prediction of near-wall turbulence. For steady wall-bounded turbulent flows, we make the equilibrium assumption between rates of production ($P$) and dissipation ($\epsilon $) of turbulent kinetic energy ($k$) in the near-wall region to propose that the eddy viscosity should be given by ${\nu }_{t} \approx \epsilon / {S}^{2} $, where $S$ is the mean shear rate. We then argue that the appropriate velocity scale is given by $\mathop{(S{T}_{L} )}\nolimits ^{- 1/ 2} {k}^{1/ 2} $ where ${T}_{L} = k/ \epsilon $ is the turbulence (decay) time scale. The difference between this velocity scale and the commonly assumed velocity scale of ${k}^{1/ 2} $ is subtle but the consequences are significant for near-wall effects. We then extend our discussion to show that the fundamental length and time scales that capture the near-wall behaviour in wall-bounded shear flows are the shear mixing length scale ${L}_{S} = \mathop{(\epsilon / {S}^{3} )}\nolimits ^{1/ 2} $ and the mean shear time scale $1/ S$, respectively. With these appropriate length and time scales (or equivalently velocity and time scales), the eddy viscosity can be rewritten in the familiar form of the $k$–$\epsilon $ model as ${\nu }_{t} = \mathop{(1/ S{T}_{L} )}\nolimits ^{2} {k}^{2} / \epsilon $. We use the direct numerical simulation (DNS) data of turbulent channel flow of Hoyas & Jiménez (Phys. Fluids, vol. 18, 2006, 011702) and the turbulent boundary layer flow of Jiménez et al. (J. Fluid Mech. vol. 657, 2010, pp. 335–360) to perform ‘a priori’ tests to check the validity of the revised eddy viscosity formulation. The comparisons with the exact computations from the DNS data are remarkable and highlight how well the equilibrium assumption holds in the near-wall region. These findings could prove to be useful in near-wall modelling of turbulent flows.

Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

2019 ◽  
Vol 234 (3) ◽  
pp. 796-807
Author(s):  
Zi-Liang Zhang ◽  
Ming-Ming Zhang ◽  
Chang Cai ◽  
Yu Cheng
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Small Scale ◽  
Wall Region ◽  
Hot Wire ◽  
Logarithmic Region ◽  
Scale Structures ◽  
Riblet Surface ◽  
Small Scale Structures ◽  
Near Wall

Riblet is one of the most promising passive drag reduction techniques in turbulent flows. In this paper, hot-wire measurements on a turbulent boundary layer perturbed by a drag-reducing riblet surface are carried out to further understand the riblet effects on the turbulent flows and the drag reduction mechanism. Compared with the smooth case, different energy variations in the near-wall region and the logarithmic region are observed over riblets. Then, by using a spectral filter of a given wavelength, the time series of the hot-wire data are decomposed into large- and small-scale components. It is indicated that large-scale structures in the logarithmic region impose a footprint (amplitude modulating effect) on the near-wall small-scale structures. By quantifying this footprint, it is found that the interactions between large- and small-scale structures over riblets are weakened in the near-wall region. Furthermore, the bursting process of large and small scales is studied. For both large- and small-scale structures, a shorter bursting duration and a higher bursting frequency are observed over the riblet surface, which indicates that riblets impede the formation of large- and small-scale bursting events. The flow physics behind these phenomena are also discussed in detail.

Subgrid‐scale energy transfer and near‐wall turbulence structure

1996 ◽  
Vol 8 (1) ◽  
pp. 215-224 ◽  
Author(s):  
Ugo Piomelli ◽  
Yunfang Yu ◽  
Ronald J. Adrian
Keyword(s):  
Energy Transfer ◽  
Wall Turbulence ◽  
Turbulence Structure ◽  
Subgrid Scale ◽  
Near Wall Turbulence ◽  
Near Wall

An Anisotropic Subgrid Model for Large Eddy Simulation of Wall Bounded Turbulent Flows

2007 ◽  
Author(s):  
Sachin S. Badarayani ◽  
Kyle D. Squires
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Turbulent Flows ◽  
Model Parameters ◽  
Wall Region ◽  
Outer Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

Large Eddy Simulation (LES) of high-Reynolds-number wall-bounded turbulent flows is prohibitively expensive if the energy-containing eddies in the near-wall region are resolved. This motivates the use of wall-layer models in which an approximate solution of the near wall dynamics is bridged to an LES of the outer flow. The main interest of the present work are wall-modeling strategies based on Detached Eddy Simulation (DES). In these approaches, the near-wall solution is closed using a Reynolds-averaged Navier Stokes model with a subgrid closure applied to the outer flow. As is well known, the original DES formulation applied directly as a wall model results in a shift in the velocity profile, corresponding to an under-estimation of the skin friction. A new formulation is proposed in this contribution in which the wall-parallel components of the modeled stress are reduced in order to lower the influence of the model and increase the resolved stress. The effectiveness of the new model is evaluated via comparison against DES predictions using the original and recently-proposed versions of the method. The effect of grid resolution and model parameters are also assessed using computations of turbulent channel flow at a Reynolds number based on friction velocity and channel halfwidth of 5000. The predictions show that the anisotropic form of the model stress yields an improved prediction of the mean velocity profile in better agreement with the logarithmic law and with larger resolved stress in the near-wall region.

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