Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
22
3-4
1995
Effect of Chain-Like Aggregates on Physical Properties of Magnetorheological Suspensions
1-8
A. Yu.
Zubarev
Ural State University, Ekaterinburg, Russia
L. Yu.
Iskakova
Urals State University, Ekaterinburg, Russia
An analytic model of magnetorheological suspensions with linear chain-like aggregates is suggest. The model predicts that the application of an external magnetic field whose value exceeds some threshold will induce a large number of long chains. This transformation increases the suspension's magnetic susceptibility by a factor of several tens and its effective viscosity - by a factor of several thousands.
Equations of Motion and Boundary Conditions for the Creeping Flow of a Dilute Suspension of Spheres
9-20
Daniel
Lhuillier
Laboratoire de Modélisation en Méecanique, Universitée Pierre et Marie Curie et CNRS, 8; rue du capitaine Scott, 75015 Paris, France
Flowing suspensions are limited by boundaries and to describe the flow one has two possibilities: either very complicated equations describing the whole flow and completed by simple boundary conditions, or simpler equations describing the bulk flow only and completed by more sophisticated "bulk" boundary conditions. The latter point of view is here applied to one of the simplest examples, the creeping flow of a dilute suspension of spheres. The bulk equations of motion contain forces and stresses that have been somewhat overlooked up to now. Explicit expressions are provided for the bulk boundary conditions, and one of them is shown to be extremely sensitive to the particle distribution in the boundary layers. We apply these equations and boundary conditions to the sedimentation flow between parallel vertical plates, and suggest that the assumption of a homogeneous distribution of centers is not always pertinent, even for dilute suspensions.
An Order of Magnitude Analysis of the Two-Phase K-ε Model
21-44
Christophe
Morel
Commissariat a l'Energie Atomique, DEN/DM2S/STMF/LMSF, 17; rue des Martyrs, 38054, Grenoble, Cedex 9, France
The objective of this paper is to derive a set of equations for modeling the statistical effects of turbulence in the context of the multidimensional two-fluid model for two-phase flows. Two-phase K-ε models based on the local instant formulation and its averaging have been developed by several authors. These models result in sets of very complicated equations including many interfacial interaction terms in addition to the phasic terms already appearing in single phase K-ε equations. The purpose of this paper is to simplify the equations of the two-phase K-ε model by performing a scale analysis analogous to Lumley's one done for turbulent single phase flows. There appear two nondimensional numbers, the turbulent Reynolds number of phase k, that was already present in the single-phase case, and another nondimensional number that represents the magnitude ratio between the interfacial interaction terms and the phasic terms pertaining to phase k. In the case of dispersed bubbly flows, we then propose a simplification of the two-phase K-ε model for dispersed bubbly flows based on an analysis of existing experimental data. We show that the dissipation rate equation can be considerably simplified.
Modeling External Heat Exchange in Infiltrated Particulate Beds
45-83
Yu. A.
Buyevich
CRSS, University of California, Santa Barbara, USA
A generalized formulation is proposed to treat different heat transfer problems for a solid body immersed in an infiltrated granular bed. Heat transport within the bed is due to 1) molecular heat conduction, and 2) convective heat dispersion. The convective contribution to the effective heat conductivity is spatially nonuniform since it is proportional to the fluid filtration velocity which varies outside the body, and this contribution 1) enhance heat removal from the body, and 2) substantially affects the distribution of heat transfer coefficient over the body surface. Steady heat transfer boundary problems of the first and second kind are considered for immersed cylinders, spheres and plates. The corresponding theoretical conclusions are in satisfactory agreement with experimental evidence. Self-similar solutions to unsteady heat transfer problems are obtained by using the thin boundary layer approximation. Unsteady problems for heat transfer that is accompanied by heat absorption in the bulk of the bed are reduced to corresponding problems without absorption. The influence of the excessive porosity layer that originates near the body surface due to this surface impenetrability for solid bed particles is discussed. In particular, if the particle material conducts heat better than the interstitial fluid, this layer is shown to reduce boundary conditions of the first kind to those of the third kind and to essentially diminish heat transfer rates.
Unsteady Vapor-Drop Jet in Rarefied Space
84-93
Z. M.
Malikov
Al'bert Leonidovich
Stasenko
Central Aerohydrodynamic Institute, Zhukovsky, Moscow region, Russia, 140180
Unsteady axisymmetric effusion of polydisperse vapor-drop mixture into a rarefied space is studied taking into account nonequilibrium interphase mass, momentum, and energy exchange. Droplet collision, gas dynamic breakup, crystallization, and spontaneous vapor condensation are not assumed to occur. A stream with fading mass flow oscillations is calculated as an example. A timesaving algorithm is used for solving equations of (i) quasi-steady two-dimensional flow in the nozzle and a near wake and (ii) unsteady one-dimensional flow in the jet far field.
Computation of Flow in Mixing Units with Lobe Extensions
94-105
V. I.
Vasil'yev
Central Institute for Aviation Motors Zhukovsky, Russia
S. N.
Zakotenko
Central Institute for Aviation Motors Zhukovsky, Russia
Sergei Yu.
Krasheninnikov
Central Institute of Aviation Motors (CIAM), 2 Aviamotornaya St., Moscow, 111116, Russia
S. V.
Khokhlov
Central Institute for Aviation Motors Zhukovsky, Russia
S. G.
Serovayev
Central Institute for Aviation Motors Zhukovsky, Russia
A. A.
Snitko
Central Institute for Aviation Motors Zhukovsky, Russia
A method for computation of three-dimensional turbulent flows in mixing units of bypass turbojet engines in which lobe extensions are used to intensify mixing is suggested. The flow upstream of the lobe extension exit is subdivided into a potential core and a boundary layer. The potential flow is computed by the Boundary Integral Equations Method, and the viscous flow is calculated by an integral method for three-dimensional turbulent boundary layer. The flow in the mixing chamber is computed by the parabolic Reynolds equations and a one-parametric turbulence model. Flows in a set of mixing devices have been computed. The results are shown to be in agreement with experimental data.