Modulation of turbulence by dispersed solid particles in a spatially developing flat-plate boundary layer

2016 ◽  
Vol 802 ◽  
pp. 359-394 ◽  
Author(s):  
Dong Li ◽  
Kun Luo ◽  
Jianren Fan
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Fluid Velocity ◽  
Plate Boundary ◽  
Stokes Number ◽  
Point Particle ◽  
Solid Particles ◽  
Inertial Particles ◽  
Mass Loading ◽  
Turbulence Modulation

Direct numerical simulations of particle-laden spatially developing turbulent boundary layers over a flat plate have been performed to investigate the effect of inertial particles on turbulence modulation, using the Eulerian–Lagrangian point-particle approach with two-way coupling. The particles are smaller than the Kolmogorov length scale of the dilute flow, and inter-particle collisions are not considered. The simulation results show that the addition of small solid particles increases the mean streamwise fluid velocity, which in turn leads to a reduction in the boundary layer integral parameters and an increase in the skin-friction drag. These effects become more pronounced as the particle Stokes number and mass loading increase. The streamwise turbulence intensity is slightly enhanced in the close vicinity of the wall but damped in the outer layer. In contrast, the Reynolds stress and the turbulence intensities in the wall-normal and spanwise directions are substantially attenuated across the entire boundary layer, and the levels of attenuation increase monotonically with both particle Stokes number and mass loading. The exchange of kinetic energy between particles and fluid indicates that particle–fluid interactions cause extra energy dissipation, which plays a crucial role in turbulence modulation.

scholarly journals Concentration and velocity statistics of inertial particles in upward and downward pipe flow

2017 ◽  
Vol 822 ◽  
pp. 640-663 ◽  
Author(s):  
J. L. G. Oliveira ◽  
C. W. M. van der Geld ◽  
J. G. M. Kuerten
Keyword(s):  
Liquid Velocity ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Stokes Number ◽  
Terminal Velocity ◽  
Point Particle ◽  
Inertial Particles ◽  
Carrier Fluid ◽  
Velocity Statistics ◽  
The Difference

Three-dimensional particle tracking velocimetry is applied to particle-laden turbulent pipe flows at a Reynolds number of 10 300, based on the bulk velocity and the pipe diameter, for developed fluid flow and not fully developed flow of inertial particles, which favours assessment of the radial migration of the inertial particles. Inertial particles with Stokes number ranging from 0.35 to 1.11, based on the particle relaxation time and the radial-dependent Kolmogorov time scale, and a ratio of the root-mean-square fluid velocity to the terminal velocity of order 1 have been used. Core peaking of the concentration of inertial particles in up-flow and wall peaking in down-flow have been found. The difference in mean particle and Eulerian mean liquid velocity is found to decrease to approximately zero near the wall in both flow directions. Although the carrier fluid has all of the characteristics of the corresponding turbulent single-phase flow, the Reynolds stress of the inertial particles is different near the wall in up-flow. These findings are explained from the preferential location of the inertial particles with the aid of direct numerical simulations with the point-particle approach.

scholarly journals Experimental study of inertial particles clustering and settling in homogeneous turbulence

2019 ◽  
Vol 864 ◽  
pp. 925-970 ◽  
Author(s):  
Alec J. Petersen ◽  
Lucia Baker ◽  
Filippo Coletti
Keyword(s):  
Reynolds Number ◽  
Fluid Velocity ◽  
Stokes Number ◽  
Terminal Velocity ◽  
Solid Particles ◽  
Homogeneous Turbulence ◽  
Small Scale ◽  
Inertial Particles ◽  
Mean Flow ◽  
Integral Scale

We study experimentally the spatial distribution, settling and interaction of sub-Kolmogorov inertial particles with homogeneous turbulence. Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases. The turbulence Reynolds number based on the Taylor microscale ranges from $Re_{\unicode[STIX]{x1D706}}\approx 200{-}500$, while the particle Stokes number based on the Kolmogorov scale varies between $St_{\unicode[STIX]{x1D702}}=O(1)$ and $O(10)$. Clustering is confirmed to be most intense for $St_{\unicode[STIX]{x1D702}}\approx 1$, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of $St_{\unicode[STIX]{x1D702}}\approx 1$ particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.

Stochastic Large Eddy Simulation of Bluff-Body Two-Way-Coupled Gas-Particle Turbulent Flow

2011 ◽  
Author(s):  
Abdallah Sofiane Berrouk ◽  
Dominique Laurence
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Fluid Velocity ◽  
Solid Particles ◽  
High Mass ◽  
Steady Increase ◽  
Inertial Particles ◽  
Turbulence Modulation ◽  
Eddy Simulation ◽  
Large Eddy

With the steady increase in computing power, there have been numerous efforts to numerically quantify turbulence modulation by inertial particles. However, highly resolving the flow around thousands to millions of particles to get an accurate particle/turbulence interaction has been prohibited by the number of grid points required. Thus, physical models have been developed and “plugged” to well-resolved numerical simulations to render prediction of turbulence modulation tractable. In this work, flow turbulence modulation by dispersed solid particles in a bluff body was studied using two-way-coupled stochastic large eddy simulation. Point-force scheme was used to model the inertial particle back effects on the fluid motion. The fluid velocity field seen by inertial particles was stochastically constructed based on the filtered flow field obtained from well resolved large eddy simulations. For that purpose a Langevin-type stochastic diffusion process was used with the necessary modifications to account for particle inertia, cross-trajectory effects and the two-way coupling. The numerical results regarding mean and turbulence statistics for the fluid phase show a very good agreement with the experimental findings for both low and high mass loadings (22% and 110% respectively). This numerical investigation demonstrates also the ability of the stochastic-LES-particle approach to predict turbulence modification by inertial particles.

Deposition of Fine Solid Particles in Laminar Flat-Plate Boundary Layers

2007 ◽  
Author(s):  
M. Hussainov ◽  
A. Kartushinsky ◽  
E. E. Michaelides ◽  
Y. Rudi ◽  
I. Shcheglov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Mass Concentration ◽  
Plate Boundary ◽  
Solid Particles ◽  
Particle Mass ◽  
Surface Velocity ◽  
Deposition Flux ◽  
Plate Surface ◽  
Particle Mass Concentration

A method for the assessment of the deposition of fine solid particles in a vertical two-phase laminar flat-plate boundary layer is presented. The method is based on a probabilistic approach to the particles deposition and takes into account both the hydrodynamics of the flow past the plate and the adhesive properties of particles and the plate surface. Electrocorundum powders with particle sizes of 12, 23 and 32 μm were used for the investigations. A stainless steel hollow conical shape was used as a prototype surface for the particles deposition. The experimental investigation used the centrifugal technique for the deposition of particles and examined pairs of particles and surfaces for the characteristics of the deposition process. The results exhibited the typical log-normal distributions of the dependence of the deposition/adhesion process. An overall expression for the particles deposition flux was derived. The expression includes the normal to the surface velocity of the particles, the particle mass concentration observed immediately close to the surface of the plate and the surface of the plate. The hydrodynamic properties of the dispersed phase in the vicinity of the plate surface, namely the normal velocity and the particle mass concentration, were calculated by the mathematical model of the flat-plate laminar boundary layer elaborated in [1]. The validation of the proposed method of assessment of deposition was accomplished by comparing the deposition flux calculated along the plate with experimental data obtained in [2]. A small discrepancy between the numerical and experimental results was observed, which may be attributed to neglecting the microphysics of adhesion, such as the influence of the electric charges and humidity during the experiments.

Interaction of intersecting shocks with a flat-plate boundary layer in the presence of an entropy layer

2013 ◽  
Vol 48 (5) ◽  
pp. 636-647 ◽  
Author(s):  
V. Ya. Borovoy ◽  
I. V. Egorov ◽  
V. E. Mosharov ◽  
V. N. Radchenko ◽  
A. S. Skuratov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Plate Boundary ◽  
Entropy Layer ◽  
Flat Plate Boundary Layer

scholarly journals A Theory for Wake-Induced Transition

1989 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Free Stream ◽  
Plate Boundary ◽  
Transition Model ◽  
Model Comparisons ◽  
Turbulent Wakes ◽  
Flat Plate Boundary Layer

A theory for transition from laminar to turbulent flow as the result of unsteady, periodic passing of turbulent wakes in the free stream is developed using Emmons’ transition model. Comparisons made to flat plate boundary layer measurements and airfoil heat transfer measurements confirm the theory.

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