Singularity of Inertial Particle Concentration in the Viscous Sublayer of Wall-bounded Turbulent Flows

2013 ◽  
Vol 92 (1-2) ◽  
pp. 41-64 ◽  
Author(s):  
Dmitrii Ph. Sikovsky
Keyword(s):  
Turbulent Flows ◽  
Particle Concentration ◽  
Viscous Sublayer ◽  
Inertial Particle

On the near-wall characteristics of acceleration in turbulence

2010 ◽  
Vol 659 ◽  
pp. 405-419 ◽  
Author(s):  
K. YEO ◽  
B.-G. KIM ◽  
C. LEE
Keyword(s):  
Turbulent Flows ◽  
Streamwise Vortex ◽  
Reynolds Numbers ◽  
Viscous Sublayer ◽  
Centripetal Acceleration ◽  
Vortical Structures ◽  
Turbulent Channel Flows ◽  
Background Shear ◽  
Kolmogorov Constant ◽  
Near Wall

The behaviour of fluid-particle acceleration in near-wall turbulent flows is investigated in numerically simulated turbulent channel flows at low to moderate Reynolds numbers, Reτ = 180~600). The acceleration is decomposed into pressure-gradient (irrotational) and viscous contributions (solenoidal acceleration) and the statistics of each component are analysed. In near-wall turbulent flows, the probability density function of acceleration is strongly dependent on the distance from the wall. Unexpectedly, the intermittency of acceleration is strongest in the viscous sublayer, where the acceleration flatness factor of O(100) is observed. It is shown that the centripetal acceleration around coherent vortical structures is an important source of the acceleration intermittency. We found sheet-like structures of strong solenoidal accelerations near the wall, which are associated with the background shear modified by the interaction between a streamwise vortex and the wall. We found that the acceleration Kolmogorov constant is a linear function of y+ in the log layer. The Reynolds number dependence of the acceleration statistics is investigated.

scholarly journals Velocity transformation for compressible wall-bounded turbulent flows with and without heat transfer

2021 ◽  
Vol 118 (34) ◽  
pp. e2111144118 ◽  
Author(s):  
Kevin Patrick Griffin ◽  
Lin Fu ◽  
Parviz Moin
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flows ◽  
Viscous Sublayer ◽  
Mean Velocity ◽  
General Transformation ◽  
Law Of The Wall ◽  
Velocity Transformation ◽  
Logarithmic Region ◽  
Logarithmic Layer

In this work, a transformation, which maps the mean velocity profiles of compressible wall-bounded turbulent flows to the incompressible law of the wall, is proposed. Unlike existing approaches, the proposed transformation successfully collapses, without specific tuning, numerical simulation data from fully developed channel and pipe flows, and boundary layers with or without heat transfer. In all these cases, the transformation is successful across the entire inner layer of the boundary layer (including the viscous sublayer, buffer layer, and logarithmic layer), recovers the asymptotically exact near-wall behavior in the viscous sublayer, and is consistent with the near balance of turbulence production and dissipation in the logarithmic region of the boundary layer. The performance of the transformation is verified for compressible wall-bounded flows with edge Mach numbers ranging from 0 to 15 and friction Reynolds numbers ranging from 200 to 2,000. Based on physical arguments, we show that such a general transformation exists for compressible wall-bounded turbulence regardless of the wall thermal condition.

Two-Fluid Large-Eddy Simulation Approach for Gas-Particle Turbulent Flows Using Equilibrium Assumption

2006 ◽  
Author(s):  
Babak Shotorban ◽  
S. Balachandar
Keyword(s):  
Velocity Field ◽  
Gas Phase ◽  
Turbulent Flows ◽  
Particle Concentration ◽  
Particle Flux ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Particle ◽  
Two Fluid

This article illustrates a two-fluid large-eddy simulation (LES) approach for gas-particle turbulent flows. The equilibrium assumption in which the velocity of particles is approximated in terms of the velocity and acceleration of the gas phase, is made for the development of gas-particle LES formulation in this study. A filtered Eulerian velocity field is defined for particles and expressed in terms of the temporal and spatial derivatives of the gas-phase filtered velocity field. Also, filtered particle concentration defined in the Eulerian framework is governed by a transport equation with a closure problem resulted from filtering the particle concentration nonlinear convection term and in the form of subgrid-scale particle flux. A Smagorinsky kind of formulation is used to model the subgrid-scale particle flux and close the transport equation of the filtered particle concentration. The developed gas-particle LES formulation is implemented in a homogeneous shear turbulence configuration and results are discussed. It is shown that the equilibrium assumption is valid for sufficiently small particle time constants through conducting the direct numerical simulation of the same configuration.

Direct Numerical Simulation of Gas-Particle Turbulent Swirling Flows in an Axially Rotating Pipe

2003 ◽  
Author(s):  
Kazuyoshi Matsuzaki ◽  
Mizue Munekata ◽  
Hideki Ohba
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Particle Concentration ◽  
Fluid Motion ◽  
Swirling Flows ◽  
Particle Collisions ◽  
Pipe Radius ◽  
The One ◽  
Very High

The purpose of this study is to investigate the effect of the turbulent structure of the swirling flows on the particle motions using numerical simulation. In this work, we deal with the swirling turbulent flows in an axially rotating pipe because of focusing on the influence of swirl effect on the particle motions. Direct numerical simulation (DNS) of gas-particle turbulent swirling flows in the axially rotating pipe at the Reynolds number 180, based on the friction velocity and the pipe radius, and the rotating ratios 0.25 and 0.3 based on the bulk velocity was performed. Particle motions were treated by a Lagragian method with inter-particle collisions calculated by a deterministic method. In order to investigate the influence of swirl effect on the particle motions in detail, the one-way method in which fluid motion is not affected by particles is adopted. In particular, the effect of the inter-particle collisions on particle motions was carefully investigated because it is considered that particles accumulate near the wall due to the centrifugal force and local particle concentration is very high in the region.

Direct numerical simulation of scalar transport in turbulent flows over progressive surface waves

2017 ◽  
Vol 819 ◽  
pp. 58-103 ◽  
Author(s):  
Di Yang ◽  
Lian Shen
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Viscous Sublayer ◽  
Wall Turbulence ◽  
Scalar Transport ◽  
Wave Age ◽  
Wave Surface ◽  
Scalar Flux ◽  
Flat Wall

The transport of passive scalars in turbulent flows over progressive water waves is studied using direct numerical simulation. A combined pseudo-spectral and finite-difference scheme on a wave-surface-fitted grid is used to simulate the flow and scalar fields above the wave surface. Three representative wave ages (i.e. wave-to-wind speed ratios) are considered, corresponding to slow, intermediate and fast wind-waves, respectively. For each wave condition, four Schmidt numbers are considered for the scalar transport. The presence of progressive surface waves is found to induce significant wave-phase-correlated variation to the scalar field, with the phase dependence varying with the wave age. The time- and plane-averaged profiles of the scalar over waves of various ages exhibit similar vertical structures as those found in turbulence over a flat wall, but with the von Kármán constant and effective wave surface roughness for the mean scalar profile exhibiting considerable variation with the wave age. The profiles of the root-mean-square scalar fluctuations and the horizontal scalar flux exhibit good scaling in the viscous sublayer that agrees with the scaling laws previously reported for flat-wall turbulence, but with noticeable wave-induced variation in the viscous wall region. The profiles of the vertical scalar flux in the viscous sublayer exhibit apparent discrepancies from the reported scaling law for flat-wall turbulence, due to a negative vertical flux region above the windward face of the wave crest. Direct observation and quadrant-based conditional averages indicate that the wave-dependent distributions of the scalar fluctuations and fluxes are highly correlated with the coherent vortical structures in the turbulence, which exhibit clear wave-dependent characteristics in terms of both shape and preferential location.

scholarly journals Single inertial particle statistics in turbulent flows from Lagrangian velocity models

2022 ◽  
Vol 7 (1) ◽  
Author(s):  
Jan Friedrich ◽  
Bianca Viggiano ◽  
Mickael Bourgoin ◽  
Raúl Bayoán Cal ◽  
Laurent Chevillard
Keyword(s):  
Turbulent Flows ◽  
Inertial Particle ◽  
Velocity Models ◽  
Lagrangian Velocity ◽  
Particle Statistics

scholarly journals Interpretation of the mechanism associated with turbulent drag reduction in terms of anisotropy invariants

2007 ◽  
Vol 577 ◽  
pp. 457-466 ◽  
Author(s):  
B. FROHNAPFEL ◽  
P. LAMMERS ◽  
J. JOVANOVIĆ ◽  
F. DURST
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Viscous Sublayer ◽  
Direct Numerical Simulations ◽  
Wall Region ◽  
Turbulent Drag Reduction ◽  
High Anisotropy ◽  
Turbulent Drag ◽  
Reduction Mechanisms ◽  
Long Chain

A central goal of flow control is to minimize the energy consumption in turbulent flows and nowadays the best results in terms of drag reduction are obtained with the addition of long-chain polymers. This has been found to be associated with increased anisotropy of turbulence in the near-wall region. Other drag reduction mechanisms are analysed in this respect and it is shown that close to the wall highly anisotropic states of turbulence are commonly found. These findings are supported by results of direct numerical simulations which display high drag reduction effects of over 30% when only a few points inside the viscous sublayer are forced towards high anisotropy.

Mobility Deposition Effect of Aerosol Particles in the Boundary Layer

2013 ◽  
Vol 300-301 ◽  
pp. 924-927
Author(s):  
Ming Chi Chiou ◽  
Wen Zong Hsu
Keyword(s):  
Boundary Layer ◽  
Particle Deposition ◽  
Particle Concentration ◽  
Fluid Motion ◽  
Viscous Sublayer ◽  
Boundary Layer Flows ◽  
Random Surface ◽  
Surface Renewal ◽  
Developed Turbulence ◽  
Deposition Effect

The particle concentration and convection velocity profile has been obtained by the adaptation of the random surface renewal model to the particle continuity and momentum equations of the nonisothermal turbulence boundary-layer flows In general, the investigations of particle deposition mainly include incompressible fluid laden by spherical and dilute particles in the fully developed turbulence boundary layer flows. This means that the fluid motion is unaffected by the presence of the particles and that the collisions between particles can be neglected. the relative quiescent viscous sublayer, resulting in the increase in thermophoretic deposition with increased Prandtl number.

scholarly journals Particle transport in turbulent curved pipe flow

2016 ◽  
Vol 793 ◽  
pp. 248-279 ◽  
Author(s):  
Azad Noorani ◽  
Gaetano Sardina ◽  
Luca Brandt ◽  
Philipp Schlatter
Keyword(s):  
Turbulent Flows ◽  
Particle Transport ◽  
Carrier Phase ◽  
Solid Phase ◽  
Viscous Sublayer ◽  
Companion Paper ◽  
Current Data ◽  
Spherical Particles ◽  
Data Set ◽  
Curved Pipe

Direct numerical simulations (DNS) of particle-laden turbulent flow in straight, mildly curved and strongly bent pipes are performed in which the solid phase is modelled as small heavy spherical particles. A total of seven populations of dilute particles with different Stokes numbers, one-way coupled with their carrier phase, are simulated. The objective is to examine the effect of the curvature on micro-particle transport and accumulation. It is shown that even a slight non-zero curvature in the flow configuration strongly impact the particle concentration map such that the concentration of inertial particles with bulk Stokes number $0.45$ (based on bulk velocity and pipe radius) at the inner bend wall of mildly curved pipe becomes $12.8$ times larger than that in the viscous sublayer of the straight pipe. Near-wall helicoidal particle streaks are observed in the curved configurations with their inclination varying with the strength of the secondary motion of the carrier phase. A reflection layer, as previously observed in particle laden turbulent S-shaped channels, is also apparent in the strongly curved pipe with heavy particles. In addition, depending on the curvature, the central regions of the mean Dean vortices appear to be completely depleted of particles, as observed also in the partially relaminarised region at the inner bend. The turbophoretic drift of the particles is shown to be affected by weak and strong secondary motions of the carrier phase and geometry-induced centrifugal forces. The first- and second-order moments of the velocity and acceleration of the particulate phase in the same configurations are addressed in a companion paper by the same authors. The current data set will be useful for modelling particles advected in wall-bounded turbulent flows where the effects of the curvature are not negligible.

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