Effect of Particle Size on Velocity Correlations in Turbulent Channel Flow

2003 ◽  
Author(s):  
Daniel A. Khalitov ◽  
Ellen K. Longmire
Keyword(s):  
Channel Flow ◽  
Particle Velocity ◽  
Single Point ◽  
Turbulent Channel Flow ◽  
Dual Frame ◽  
Spanwise Direction ◽  
Particle Correlation ◽  
Particle Correlations ◽  
Velocity Statistics ◽  
Point Velocity

The response of glass beads was examined in a fully developed turbulent channel flow of air with Reynolds number Reh = 4500 where h is the channel half width. Five sets of monodisperse particles were tested with integral Stokes numbers in the range 0.2–10 at the channel centerplane. Particle-to-air mass loadings were of order 10%. Laser sheets were aligned in streamwise-spanwise flow planes, and seeded, particle-laden flow was imaged with a dual-frame camera. A separation algorithm was used to obtain simultaneous gas and particle velocity measurements of homogeneous flow planes over a range of wall-normal distances. Profiles of single-point velocity statistics including mean and rms slip velocity, particle drift velocity, and gas-particle correlation were computed. In addition, two-point gas-particle and particle-particle velocity correlations were obtained. Near the wall, the gas-gas correlations yielded long, narrow patterns related to near-wall low-speed streaks. At the centerplane, the correlations were broader in the spanwise direction. Gas-particle and particle-particle correlations resembled the gas correlations in shape and size, but the values were smaller. The gas-particle covariance tended toward zero for St = 10. Particle-particle correlations were still significant for St = 4.

scholarly journals Turbulent channel flow over an anisotropic porous wall – drag increase and reduction

2018 ◽  
Vol 842 ◽  
pp. 381-394 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Brandt ◽  
Alfredo Pinelli
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
High Speed ◽  
Vertical Direction ◽  
Porous Wall ◽  
Turbulent Channel Flow ◽  
Spanwise Direction ◽  
Normal Velocity ◽  
Porous Walls ◽  
The One

The effect of the variations of the permeability tensor on the close-to-the-wall behaviour of a turbulent channel flow bounded by porous walls is explored using a set of direct numerical simulations. It is found that the total drag can be either reduced or increased by more than 20 % by adjusting the permeability directional properties. Drag reduction is achieved for the case of materials with permeability in the vertical direction lower than the one in the wall-parallel planes. This configuration limits the wall-normal velocity at the interface while promoting an increase of the tangential slip velocity leading to an almost ‘one-component’ turbulence where the low- and high-speed streak coherence is strongly enhanced. On the other hand, strong drag increase is found when high wall-normal and low wall-parallel permeabilities are prescribed. In this condition, the enhancement of the wall-normal fluctuations due to the reduced wall-blocking effect triggers the onset of structures which are strongly correlated in the spanwise direction, a phenomenon observed by other authors in flows over isotropic porous layers or over ribletted walls with large protrusion heights. The use of anisotropic porous walls for drag reduction is particularly attractive since equal gains can be achieved at different Reynolds numbers by rescaling the magnitude of the permeability only.

High Order Lagrangian Velocity Statistics in a Turbulent Channel Flow with Re τ = 80

2012 ◽  
Vol 24 (2) ◽  
pp. 287-291 ◽  
Author(s):  
Jian-ping Luo ◽  
Xiang Qiu ◽  
Dong-mei Li ◽  
Yu-lu Liu
Keyword(s):  
Channel Flow ◽  
Turbulent Channel Flow ◽  
High Order ◽  
Velocity Statistics ◽  
Lagrangian Velocity

Equilibrium-Eulerian LES Model for Turbulent Poly-dispersed Particle-laden Flow

2013 ◽  
Vol 14 (2) ◽  
Author(s):  
Matteo Icardi ◽  
Daniele L. Marchisio ◽  
Narayanan Chidambaram ◽  
Rodney O. Fox
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Channel Flow ◽  
Particle Velocity ◽  
Turbulent Channel Flow ◽  
Scale Model ◽  
Phase System ◽  
Deconvolution Method ◽  
Approximate Deconvolution

AbstractAn efficient Eulerian method for poly-dispersed particles in turbulent flows is implemented, verified and validated for a channel flow. The approach couples a mixture model with a quadrature-based moment method for the particle size distribution in a LES framework, augmented by an approximate deconvolution method to reconstructs the unfiltered velocity. The particle velocity conditioned on particle size is calculated with an equilibrium model, valid for low Stokes numbers. A population balance equation is solved with the direct quadrature method of moments, that efficiently represents the continuous particle size distribution. In this first study particulate processes are not considered and the capability of the model to properly describe particle transport is investigated for a turbulent channel flow. First, single-phase LES are validated through comparison with DNS. Then predictions for the two-phase system, with particles characterised by Stokes numbers ranging from 0.2 to 5, are compared with Lagrangian DNS in terms of particle velocity and accumulation at the walls. Since this phenomenon (turbophoresis) is driven by turbulent fluctuations and depends strongly on the particle Stokes number, the approximation of the particle size distribution, the choice of the sub-grid scale model and the use of an approximate deconvolution method are important to obtain good results. Our method can be considered as a fast and efficient alternative to classical Lagrangian methods or Eulerian multi-fluid models in which poly-dispersity is usually neglected.

scholarly journals Numerical simulation of turbulent channel flow over a viscous hyper-elastic wall

2017 ◽  
Vol 830 ◽  
pp. 708-735 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Brandt
Keyword(s):  
Channel Flow ◽  
Solid Phase ◽  
Turbulent Channel Flow ◽  
Inertial Range ◽  
Spanwise Direction ◽  
Logarithmic Scale ◽  
Normal Velocity ◽  
Mean Velocity ◽  
Elastic Wall ◽  
Hyper Elastic

We perform numerical simulations of a turbulent channel flow over an hyper-elastic wall. In the fluid region the flow is governed by the incompressible Navier–Stokes (NS) equations, while the solid is a neo-Hookean material satisfying the incompressible Mooney–Rivlin law. The multiphase flow is solved with a one-continuum formulation, using a monolithic velocity field for both the fluid and solid phase, which allows the use of a fully Eulerian formulation. The simulations are carried out at Reynolds bulk $Re=2800$ and examine the effect of different elasticity and viscosity of the deformable wall. We show that the skin friction increases monotonically with the material elastic modulus. The turbulent flow in the channel is affected by the moving wall even at low values of elasticity since non-zero fluctuations of vertical velocity at the interface influence the flow dynamics. The near-wall streaks and the associated quasi-streamwise vortices are strongly reduced near a highly elastic wall while the flow becomes more correlated in the spanwise direction, similarly to what happens for flows over rough and porous walls. As a consequence, the mean velocity profile in wall units is shifted downwards when shown in logarithmic scale, and the slope of the inertial range increases in comparison to that for the flow over a rigid wall. We propose a correlation between the downward shift of the inertial range, its slope and the wall-normal velocity fluctuations at the wall, extending results for the flow over rough walls. We finally show that the interface deformation is determined by the fluid fluctuations when the viscosity of the elastic layer is low, while when this is high the deformation is limited by the solid properties.

A wind tunnel study of air flow in waving wheat: Single-point velocity statistics

1994 ◽  
Vol 70 (1-2) ◽  
pp. 95-132 ◽  
Author(s):  
Y. Brunet ◽  
J. J. Finnigan ◽  
M. R. Raupach
Keyword(s):  
Wind Tunnel ◽  
Single Point ◽  
Air Flow ◽  
Velocity Statistics ◽  
Point Velocity ◽  
Wind Tunnel Study

Statistics of Particle Suspensions in Turbulent Channel Flow

2012 ◽  
Vol 11 (4) ◽  
pp. 1311-1322 ◽  
Author(s):  
Lihao Zhao ◽  
Helge I. Andersson
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Particle Concentration ◽  
Response Times ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Channel Height ◽  
Velocity Statistics ◽  
The Mean ◽  
Particle Velocities

AbstractParticle dynamics in a turbulent channel flow is considered. The effects of particle concentration and Reynolds number on the particle velocity statistics are investigated. Four different particle response times, τ+=1, 5, 30 and 100, are examined for three different Reynolds numbers, Re*=200, 360 and 790 (based on channel height and friction velocity). The particle concentration evolves with time and statistics obtained during three different sampling periods might be distinctly different. The mean and fluctuating particle velocities are substantially affected both by the particle response time and by the Reynolds number of the flow.

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