Four-way coupled simulations of small particles in turbulent channel flow: The effects of particle shape and Stokes number

2015 ◽  
Vol 27 (8) ◽  
pp. 083301 ◽  
Author(s):  
F. Zhao ◽  
W. K. George ◽  
B. G. M. van Wachem
Keyword(s):  
Channel Flow ◽  
Particle Shape ◽  
Turbulent Channel Flow ◽  
Stokes Number ◽  
Small Particles

Deposition of Small Particles From Turbulent Flows

2003 ◽  
Author(s):  
Z. Wu ◽  
J. B. Young
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Channel Flow ◽  
Gas Turbines ◽  
Particle Deposition ◽  
Numerical Study ◽  
Turbulent Channel Flow ◽  
Brownian Diffusion ◽  
Small Particles ◽  
Two Fluid

This paper deals with particle deposition onto solid walls from turbulent flows. The aim of the study is to model particle deposition in industrial flows, such as the one in gas turbines. The numerical study has been carried out with a two fluid approach. The possible contribution to the deposition from Brownian diffusion, turbulent diffusion and shear-induced lift force are considered in the study. Three types of turbulent two-phase flows have been studied: turbulent channel flow, turbulent flow in a bent duct and turbulent flow in a turbine blade cascade. In the turbulent channel flow case, the numerical results from a two-dimensional code show good agreement with numerical and experimental results from other resources. Deposition problem in a bent duct flow is introduced to study the effect of curvature. Finally, the deposition of small particles on a cascade of turbine blades is simulated. The results show that the current two fluid models are capable of predicting particle deposition rates in complex industrial flows.

scholarly journals Disks aligned in a turbulent channel

2015 ◽  
Vol 772 ◽  
pp. 1-4 ◽  
Author(s):  
Greg A. Voth
Keyword(s):  
Fluid Flow ◽  
Channel Flow ◽  
Particle Shape ◽  
Particle Density ◽  
Biological Fluid ◽  
Fluid Flows ◽  
Turbulent Channel Flow ◽  
Anisotropic Particles ◽  
Wide Range ◽  
Preferential Alignment

Anisotropic particles are suspended in a wide range of industrial, environmental and biological fluid flows. The orientations of these particles are sometimes randomized by turbulence, but often they are brought into preferential alignment by the fluid flow. In a recently published study, Challabotla, Zhao & Andersson (J. Fluid Mech., vol. 766, 2015, R2) performed the first numerical simulations of inertial disks in a turbulent channel flow. They find that disks can be made to preferentially align either parallel or perpendicular to the wall depending on the particle density. Particle shape also affects alignment, particularly for lower density particles, and the alignment of disks is quite different from the alignment of fibres.

A direct numerical investigation of two-way interactions in a particle-laden turbulent channel flow

2019 ◽  
Vol 875 ◽  
pp. 1096-1144 ◽  
Author(s):  
Cheng Peng ◽  
Orlando M. Ayala ◽  
Lian-Ping Wang
Keyword(s):  
Channel Flow ◽  
Finite Size ◽  
Turbulent Channel Flow ◽  
Spherical Particles ◽  
Homogeneous Distribution ◽  
Particle Sizes ◽  
Small Particles ◽  
Particle Rotation ◽  
Turbulence Modulation ◽  
Budget Analysis

Understanding the two-way interactions between finite-size solid particles and a wall-bounded turbulent flow is crucial in a variety of natural and engineering applications. Previous experimental measurements and particle-resolved direct numerical simulations revealed some interesting phenomena related to particle distribution and turbulence modulation, but their in-depth analyses are largely missing. In this study, turbulent channel flows laden with neutrally buoyant finite-size spherical particles are simulated using the lattice Boltzmann method. Two particle sizes are considered, with diameters equal to 14.45 and 28.9 wall units. To understand the roles played by the particle rotation, two additional simulations with the same particle sizes but no particle rotation are also presented for comparison. Particles of both sizes are found to form clusters. Under the Stokes lubrication corrections, small particles are found to have a stronger preference to form clusters, and their clusters orientate more in the streamwise direction. As a result, small particles reduce the mean flow velocity less than large particles. Particles are also found to result in a more homogeneous distribution of turbulent kinetic energy (TKE) in the wall-normal direction, as well as a more isotropic distribution of TKE among different spatial directions. To understand these turbulence modulation phenomena, we analyse in detail the total and component-wise volume-averaged budget equations of TKE with the simulation data. This budget analysis reveals several mechanisms through which the particles modulate local and global TKE in the particle-laden turbulent channel flow.

scholarly journals Turbulent channel flow of a dense binary mixture of rigid particles

2017 ◽  
Vol 818 ◽  
pp. 623-645 ◽  
Author(s):  
Iman Lashgari ◽  
Francesco Picano ◽  
Pedro Costa ◽  
Wim-Paul Breugem ◽  
Luca Brandt
Keyword(s):  
Binary Mixture ◽  
Channel Flow ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Turbulent Channel Flow ◽  
Channel Height ◽  
Wall Region ◽  
Small Particles ◽  
Rigid Particles ◽  
Large Particles

We study turbulent channel flow of a binary mixture of finite-sized neutrally buoyant rigid particles by means of interface-resolved direct numerical simulations. We fix the bulk Reynolds number and total solid volume fraction, $Re_{b}=5600$ and $\unicode[STIX]{x1D6F7}=20\,\%$, and vary the relative fraction of small and large particles. The binary mixture consists of particles of two different sizes, $2h/d_{l}=20$ and $2h/d_{s}=30$ where $h$ is the half-channel height and $d_{l}$ and $d_{s}$ the diameters of the large and small particles. While the particulate flow statistics exhibit a significant alteration of the mean velocity profile and turbulent fluctuations with respect to the unladen flow, the differences between the mono-disperse and bi-disperse cases are small. However, we observe a clear segregation of small particles at the wall in binary mixtures, which affects the dynamics of the near-wall region and thus the overall drag. This results in a higher drag in suspensions with a larger number of large particles. As regards bi-disperse effects on the particle dynamics, a non-monotonic variation of the particle dispersion in the spanwise (homogeneous) direction is observed when increasing the percentage of small/large particles. Finally, we note that particles of the same size tend to cluster more at contact whereas the dynamics of the large particles gives the highest collision kernels due to a higher approaching speed.

Microbubble Transport in Turbulent Channel Flow

2003 ◽  
Author(s):  
Marion W. Vance ◽  
Kazuyasu Sugiyama ◽  
Shu Takagi ◽  
Kyle D. Squires
Keyword(s):  
Buffer Layer ◽  
Channel Flow ◽  
Carrier Phase ◽  
Stokes Equations ◽  
Concentration Field ◽  
Turbulent Channel Flow ◽  
Stokes Number ◽  
Dispersed Phase ◽  
Phase Flow ◽  
Rigid Spheres

Microbubble transport in fully developed turbulent channel flow is investigated using an Eulerian-Lagrangian approach. The carrier-phase flow is computed using Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES) of the incompressible Navier-Stokes equations. Lagrangian particle tracking is employed for a dispersed phase comprised of small, rigid spheres of negligible density compared to the carrier-phase flow and obeying an equation of motion in which the forces used to predict the motion of the bubble are drag, pressure gradient, and added mass. In general, DNS and LES yield similar predictions of the carrier phase flow and dispersed-phase properties. The bubble Stokes number is varied over a range for which the dispersed phase essentially follows the carrier flow to larger values for which strong segregation of the microbubbles into coherent vortical structures occurs. In general, simulation results show that microbubble response is not a monotonic function of the Stokes number. The most significant structure in the concentration field occurs for Stokes numbers close to the turbulence timescales in the buffer layer. More than 2/3 of the microbubble population in the buffer layer resides in coherent structures that occupy approximately 1/3 of the computational volume.

Mapping spheroid rotation modes in turbulent channel flow: effects of shear, turbulence and particle inertia

2019 ◽  
Vol 876 ◽  
pp. 19-54 ◽  
Author(s):  
Lihao Zhao ◽  
Niranjan R. Challabotla ◽  
Helge I. Andersson ◽  
Evan A. Variano
Keyword(s):  
Channel Flow ◽  
Time Scale ◽  
Turbulent Channel Flow ◽  
Stokes Number ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Rotational Behaviour ◽  
Particle Rotation ◽  
Particle Inertia ◽  
Buffer Region

The rotational behaviour of non-spherical particles in turbulent channel flow is studied by Lagrangian tracking of spheroidal point particles in a directly simulated flow. The focus is on the complex rotation modes of the spheroidal particles, in which the back reaction on the flow field is ignored. This study is a sequel to the letter by Zhao et al. (Phys. Rev. Lett., vol. 115, 2015, 244501), in which only selected results in the near-wall buffer region and the almost-isotropic channel centre were presented. Now, particle dynamics all across the channel is explored to provide a complete picture of the orientational and rotational behaviour with consideration of the effects of particle aspect ratio ranging from 0.1 to 10 and particle Stokes number from 0 (inertialess) to 30. The rotational dynamics in the innermost part of the logarithmic wall layer is particularly complex and affected not only by modest mean shear, but also by particle inertia and turbulent vorticity. While inertial disks exhibit modest preferential orientation in either the wall-normal or cross-stream direction, inertial rods show neither preferential tumbling nor spinning. Examination of the co-variances between particle orientation, particle rotation and fluid rotation vectors explains the qualitatively different ‘wall mode’ rotation and ‘centre mode’ rotation. Inertialess spheroids transition between the two modes within a narrow zone ($15<z^{+}<35$) in the buffer region. If the spheroids have inertia, the transition zone between the two modes shifts to the inner part of the logarithmic layer, i.e. $z^{+}\geqslant 40$. We ascribe the transition of inertialess spheroids from the ‘wall mode’ to the ‘centre mode’ rotation to the changeover between the time scales associated with mean shear and small-scale turbulence. Inertial spheroids, however, transition between the two rotational modes when the Kolmogorov time scale becomes comparable to the time scale for particle rotation, i.e. the effective Stokes number is of order unity. The aforementioned findings reveal, in addition to the effects of particle shape and alignment, the importance of the characteristic local time scale of fluid flow for the rotation of both tracer and inertial spheroids in turbulent channel flows.

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