Engineering June 2005 Vol 11/2 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Engineering



Volume 11 No. 2June 2005

Specialissue on interaction phenomena in multiphase flows EUROMECH Colloquium No. 447



Preface;89–90

Jüri Engelbrecht and Ülo Rudi

Comparisonbetween Lagrangian and Eulerian particle simulations coupled with DNS ofhomogeneous isotropic decaying turbulence; 91–105

André Kaufmann, Jerome Helie, Olivier Simonin andThierry Poinsot

Abstract. A direct numerical simulation (DNS) approach toEulerian–Eulerian dispersed two-phase flow is discussed. The need for a stressterm in the momentum transport equation of the dispersed phase is identifiedand a simple model for this stress term is proposed. Measurements of the dispersedphase quantities such as number density, mesoscopic velocity and stress tensorcomponents 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, turbulentdispersion, continuum approach, preferential concentration.

Physicsof inertial microparticles transfer in turbulent boundary layers;106–125

Alfredo Soldati

Abstract. Turbulent dispersed flows in boundary layers are crucial in a numberof industrial and environmental applications. In most applications, the keyinformation is particle spatial distribution and it is known that inertialparticles in turbulent flows distribute preferentially avoiding strong vorticalregions and segregating into straining regions. It is also known that, in thespecific case of boundary layers, this preferential accumulation occurs alongthe wall in a macroscopic way. Numerical and experimental works show that fluidmotions in turbulent boundary layers are intermittent and have a stronglyorganized and coherent nature, represented by the large scale motions. Thesemotions, even though not exactly repeatable and only quasi-deterministic,control the transport of the dispersed species. In this work, direct numericalsimulations of turbulence in upward boundary layers in pipes and channels andLagrangian tracking of inertial particles are employed to examine particletransfer in connection with the dynamics of the flow structures populating theboundary layer. It is argued that the local syncronicity between the events inthe turbulence regeneration cycle and the mechanisms, controlling particlefluxes toward and away from the wall, determine the macroscopic net particlefluxes.

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

Particlesscattering in particle–wall collisions and its effect on the particle-phaseflow; 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 particlenon-sphericity are analysed separately and in combination. A high-speedsubsonic gas–particle flow in a two-dimensional channel with a wedge step issimulated. The particle-phase flow patterns and concentration profiles areobtained for rough wedge surface and for particles, distributed in size. Theseresults are compared with those for smooth wedge surface and monosizedparticles.

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

Particle dynamicsand 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 particledynamics and mixing in vortex-pair-like structures. Theperturbed flow field and dynamics of small spherical particles, contained inthis flow, are studied on the basis of this solution. The particle-pathequations and well-established techniques,such as computing of Poincaré maps, is used. It is shown that the flow insidethe vortex pair can behave chaotically when a relatively thick pair (core sizeof the pair comparable with its radius) is under the influence of a periodic perturbation. This isexpected to lead to better mixing of the fluid. However, an increase of theperturbation frequency causes the appearance of regions where a boundedquasi-periodic motion occurs. These regions behave like barriers in the phasespace, reducing mixing and transport processes in the fluid. Introductionof the perturbation causes changes in the trajectories of the sphericalaerosol-type particles. For a certain range of Stokes numbers (St < 10), long-term accumulation inside the vortex pair is observed forthese particles, while the same particles in the unperturbed flow are forcedout of the pair into the ambient flow.

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

Modelsof fuel spray penetration; 154–160

Sergei Sazhin, Cyril Crua, Jin-Sik Hwang, Soo-YoungNo and

Morgan Heikal

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

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

Anexperimental study of the effect of particles on the shear stress inparticulate turbulent pipe flow; 161–168

Alexander Kartushinsky, Anatoly Mulgi, Sergei Tislerand Efstathios E.Michaelides

Abstract. Experimental data on the shear stress, exerted by a flowingmixture of solid particles in air, are presented. The data were obtained in afacility with a steel or vinyl test section. The Reynolds numbers were close to105, thus the flow was turbulent. Several types of particles withdifferent material properties were used. Low as well as intermediate-to-highvalues of the loading ratio were investigated. It was found that the reductionof the data with respect to the Gastershtadt coefficient  highlights certaintrends of the flow and makes it possible to derive some general conclusions onthe behaviour of the mixture.

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

Experimentalstudy of the effect of velocity slip and mass loading on the modification ofgrid-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 massloading on a grid-generated turbulence in gas–solid particles flow arepresented. 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 particlesenhance turbulence for small grids and attenuate it for the large ones.Turbulence enhancement and attenuation are intensified with the increase of theflow mass loading. The particles effect on turbulence changes from turbulenceattenuation for a small velocity slip to its enhancement for a large velocityslip. A criterion for the evaluation of turbulence modification in gas–solidparticles flow is proposed.

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

Instructionsto authors; 181–183