CONTENTS &
ABSTRACTS

In
English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Engineering

** **

Volume 11 No. 2
June 2005

Special
issue on interaction phenomena in multiphase flows EUROMECH Colloquium No. 447

Preface;
89–90

Jüri Engelbrecht and Ülo Rudi

Comparison
between Lagrangian and Eulerian particle simulations coupled with DNS of
homogeneous isotropic decaying turbulence; 91–105

André Kaufmann, Jerome Helie, Olivier Simonin and Thierry Poinsot

**Abstract.** A direct numerical simulation (DNS) approach to
Eulerian–Eulerian dispersed two-phase flow is discussed. The need for a stress
term in the momentum transport equation of the dispersed phase is identified
and a simple model for this stress term is proposed. Measurements of the dispersed
phase quantities such as number density, mesoscopic velocity and stress tensor
components from a reference computation, using Lagrangian particle tracking,
allows to validate the predictions of the Eulerian–Eulerian computation.

**Key words:** direct numerical simulation, solid particle, turbulent
dispersion, continuum approach, preferential concentration.

Physics
of inertial microparticles transfer in turbulent boundary layers;
106–125

Alfredo Soldati

**Abstract. **Turbulent dispersed flows in boundary layers are crucial in a number
of industrial and environmental applications. In most applications, the key
information is particle spatial distribution and it is known that inertial
particles in turbulent flows distribute preferentially avoiding strong vortical
regions and segregating into straining regions. It is also known that, in the
specific case of boundary layers, this preferential accumulation occurs along
the wall in a macroscopic way. Numerical and experimental works show that fluid
motions in turbulent boundary layers are intermittent and have a strongly
organized and coherent nature, represented by the large scale motions. These
motions, even though not exactly repeatable and only quasi-deterministic,
control the transport of the dispersed species. In this work, direct numerical
simulations of turbulence in upward boundary layers in pipes and channels and
Lagrangian tracking of inertial particles are employed to examine particle
transfer in connection with the dynamics of the flow structures populating the
boundary layer. It is argued that the local syncronicity between the events in
the turbulence regeneration cycle and the mechanisms, controlling particle
fluxes toward and away from the wall, determine the macroscopic net particle
fluxes.

**Key words:** particles, turbulence, boundary layer, coherent structures.

Particles
scattering in particle–wall collisions and its effect on the particle-phase
flow; 126–139

Yury Tsirkunov and Sergei Panfilov

**Abstract.** The scattering of particles, reflected from a rigid surface,
is numerically studied. The effects of surface roughness and particle
non-sphericity are analysed separately and in combination. A high-speed
subsonic gas–particle flow in a two-dimensional channel with a wedge step is
simulated. The particle-phase flow patterns and concentration profiles are
obtained for rough wedge surface and for particles, distributed in size. These
results are compared with those for smooth wedge surface and monosized
particles.

**Key words:** gas–particle flow, particle bouncing, surface roughness,
non-spherical particles.

Particle dynamics
and mixing in an oscillating viscous vortex pair; 140–153

Felix Kaplanski, Sergei Sazhin and Ylo Rudi

**Abstract.** A model of a viscous vortex pair,
based on a solution of the Stokes equation, is applied for studying particle
dynamics and mixing in vortex-pair-like structures. The
perturbed flow field and dynamics of small spherical particles, contained in
this flow, are studied on the basis of this solution. The particle-path
equations and well-established** **techniques,
such as computing of Poincaré maps, is used. It is shown that the flow inside
the vortex pair can behave chaotically when a relatively thick pair (core size
of the pair comparable with its radius) is under the influence of a periodic perturbation. This is
expected to lead to better mixing of the fluid. However, an increase of the
perturbation frequency causes the appearance of regions where a bounded
quasi-periodic motion occurs. These regions behave like barriers in the phase
space, reducing mixing and transport processes in the fluid. Introduction
of the perturbation causes changes in the trajectories of the spherical
aerosol-type particles. For a certain range of Stokes numbers (*St* < 10), long-term accumulation inside the vortex pair is observed for
these particles, while the same particles in the unperturbed flow are forced
out of the pair into the ambient flow.

**Key words:** viscous flow, Stokes equation, vortices, vortex pair.

Models
of fuel spray penetration; 154–160

Sergei Sazhin, Cyril Crua, Jin-Sik Hwang, Soo-Young
No and

Morgan Heikal

**Abstract. **A brief review of models of diesel fuel spray penetration, developed
at the University of Brighton, are presented. These refer to the initial stage
of spray penetration and the two-phase flow stage, when the relative velocity
between droplets and gas can be ignored. The predictions of the two-phase
models of spray penetration are compared with the results of experimental
studies. A rapid compression diesel spray rig, based at Brighton University,
and a high-pressure dimethyl ether spray chamber, based at Chungbuk National
University, have been used. In both cases the experimental results are shown to
be in agreement with the prediction of theoretical models.

**Key words:** diesel fuel spray, dimethyl ether spray, two-phase flow, spray
penetration.

An
experimental study of the effect of particles on the shear stress in
particulate turbulent pipe flow; 161–168

Alexander Kartushinsky, Anatoly Mulgi, Sergei Tisler and Efstathios E. Michaelides

**Abstract.** Experimental data on the shear stress, exerted by a flowing
mixture of solid particles in air, are presented. The data were obtained in a
facility with a steel or vinyl test section. The Reynolds numbers were close to
10^{5}, thus the flow was turbulent. Several types of particles with
different material properties were used. Low as well as intermediate-to-high
values of the loading ratio were investigated. It was found that the reduction
of the data with respect to the Gastershtadt coefficient _{} highlights certain
trends of the flow and makes it possible to derive some general conclusions on
the behaviour of the mixture.

**Key words: **gas–solid pipe flow, turbulence, loading ratio, shear stress,
Gastershtadt coefficient.

Experimental
study of the effect of velocity slip and mass loading on the modification of
grid-generated turbulence in gas–solid particles flows;
169–180

Medhat Hussainov, Alexander Kartushinsky, Ylo Rudi,

Igor Shcheglov and Sergei Tisler

**Abstract.** Experimental data on the effects of the velocity slip and mass
loading on a grid-generated turbulence in gas–solid particles flow are
presented. Glass beads (700 mm) were used as the dispersed phase.
Velocities of both phases were measured with a Laser Doppler Anemometer.
Turbulence decay curves, obtained for different grids, show that particles
enhance turbulence for small grids and attenuate it for the large ones.
Turbulence enhancement and attenuation are intensified with the increase of the
flow mass loading. The particles effect on turbulence changes from turbulence
attenuation for a small velocity slip to its enhancement for a large velocity
slip. A criterion for the evaluation of turbulence modification in gas–solid
particles flow is proposed.

**Key words:** gas–solid particles flow, grid-generated turbulence,
turbulence modification, mass loading ratio, velocity slip.

Instructions
to authors; 181–183