scholarly journals Life and death by boundary conditions

2015 ◽  
Vol 768 ◽  
pp. 1-4 ◽  
Author(s):  
Andrea Prosperetti
Keyword(s):  
Boundary Conditions ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Spherical Particles ◽  
Life And Death

Picano et al. (J. Fluid Mech., vol. 764, 2015, pp. 463–487) have conducted fully resolved numerical simulations of many thousands of spherical particles in a turbulent channel flow with $\mathit{Re}=5600$. Their results give a tantalizing demonstration of the vastness of the vistas that this line of research is about to open.

Direct numerical simulations of rotating turbulent channel flow

2008 ◽  
Vol 598 ◽  
pp. 177-199 ◽  
Author(s):  
OLOF GRUNDESTAM ◽  
STEFAN WALLIN ◽  
ARNE V. JOHANSSON
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Rotation Number ◽  
Turbulent Channel Flow ◽  
Shear Velocity ◽  
Direct Numerical Simulations ◽  
A Value ◽  
Rotation Numbers ◽  
Wall Shear ◽  
Two Sides

Fully developed rotating turbulent channel flow has been studied, through direct numerical simulations, for the complete range of rotation numbers for which the flow is turbulent. The present investigation suggests that complete flow laminarization occurs at a rotation number Ro = 2Ωδ/Ub ≤ 3.0, where Ω denotes the system rotation, Ub is the mean bulk velocity and δ is the half-width of the channel. Simulations were performed for ten different rotation numbers in the range 0.98 to 2.49 and complemented with earlier simulations (done in our group) for lower values of Ro. The friction Reynolds number Reτ = uτδ/ν (where uτ is the wall-shear velocity and ν is the kinematic viscosity) was chosen as 180 for these simulations. A striking feature of rotating channel flow is the division into a turbulent (unstable) and an almost laminarized (stable) side. The relatively distinct interface between these two regions was found to be maintained by a balance where negative turbulence production plays an important role. The maximum difference in wall-shear stress between the two sides was found to occur for a rotation number of about 0.5. The bulk flow was found to monotonically increase with increasing rotation number and reach a value (for Reτ = 180) at the laminar limit (Ro = 3.0) four times that of the non-rotating case.

scholarly journals Parametric forcing approach to rough-wall turbulent channel flow

2012 ◽  
Vol 712 ◽  
pp. 169-202 ◽  
Author(s):  
A. Busse ◽  
N. D. Sandham
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Stokes Equations ◽  
Rough Surfaces ◽  
Turbulent Channel Flow ◽  
Rough Wall ◽  
Force Term ◽  
Shape Functions ◽  
Mean Flow ◽  
The Mean

AbstractThe effects of rough surfaces on turbulent channel flow are modelled by an extra force term in the Navier–Stokes equations. This force term contains two parameters, related to the density and the height of the roughness elements, and a shape function, which regulates the influence of the force term with respect to the distance from the channel wall. This permits a more flexible specification of a rough surface than a single parameter such as the equivalent sand grain roughness. The effects of the roughness force term on turbulent channel flow have been investigated for a large number of parameter combinations and several shape functions by direct numerical simulations. It is possible to cover the full spectrum of rough flows ranging from hydraulically smooth through transitionally rough to fully rough cases. By using different parameter combinations and shape functions, it is possible to match the effects of different types of rough surfaces. Mean flow and standard turbulence statistics have been used to compare the results to recent experimental and numerical studies and a good qualitative agreement has been found. Outer scaling is preserved for the streamwise velocity for both the mean profile as well as its mean square fluctuations in all but extremely rough cases. The structure of the turbulent flow shows a trend towards more isotropic turbulent states within the roughness layer. In extremely rough cases, spanwise structures emerge near the wall and the turbulent state resembles a mixing layer. A direct comparison with the study of Ashrafian, Andersson & Manhart (Intl J. Heat Fluid Flow, vol. 25, 2004, pp. 373–383) shows a good quantitative agreement of the mean flow and Reynolds stresses everywhere except in the immediate vicinity of the rough wall. The proposed roughness force term may be of benefit as a wall model for direct and large-eddy numerical simulations in cases where the exact details of the flow over a rough wall can be neglected.

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.

Sign in / Sign up

Export Citation Format

Share Document