Showing papers on "Fluid parcel published in 1993"

A new approach to modelling viscoelastic flow

Abstract: By adapting the free Lagrangian approach (M.J. Fritts and J.P. Boris, J. Comput. Phys, 31 (1979) 173), a new numerical simulation technique for modelling viscoelastic fluid flow has been developed. Using a comoving Voronoi mesh, the method is able to track the details of fluid behaviours, e.g. deformation and stream line. The primary results include a Johnson-Segalman fluid and a single-integral Doi-Edwards fluid in a simple planar channel, and a Giesekus-Leonov fluid and an Oldroyd-B fluid in a planar 4:1 abrupt contraction at modestly high Weissenberg number. A free-surface flow is also considered.

A Single-Fluid, Self-consistent Formulation of Fluid Dynamics and Particle Transport

Abstract: We present the fluid equations for typical astrophysical plasmas, for the case of no average magnetic field and nonrelativistic flow speeds, in which particular acceleration occurs. When combined with the particle transport equation presented earlier by Williams, et al., one obtains a fully self-consistent description of particle transport and smooth fluid flow (length scales significantly larger than the mean free path). A presumed scattering law is taken for particles of all energies, and there is a single distribution function as well. This model of the interaction of particle transport, including acceleration, and fluid dynamics is in terms of four unknowns: the fluid velocity vector and the isotropic part of the particle distribution function

An experimental investigation of the flow of an electro-rheological fluid in a Rayleigh step bearing

Abstract: The transport properties of unexcited and excited electro-rheological (ER) fluid in combined Couette and Poiseuille flow are investigated. In particular the question of whether the fluid can be considered as a continuum with Bingham plastic constitutive properties, even though it is a two-phase solid-liquid mixture, is addressed. The hydrodynamic pressures generated using ER fluid in a Rayleigh step bearing at the limiting condition of zero net flow rate were measured. The properties exhibited by the fluid are compared with independently obtained data showing the continuum principle to be applicable to the flows examined.

A Computational fluid dynamics model for transient three-dimensional free surface flows

Abstract: Free surface problems occur in a variety of processes important in the manufacture of pulp and paper. Examples include black liquor spraying in a recovery furnace, jets from head boxes, the forming section of a paper machine, condensate flow in dryer cylinders, and finishing operations such as coating and polymer extrusion. The purpose of this work was to develop a computational fluid dynamics model for the analysis of some of these free surface problems. Specifically, the features added to an available computational technique have allowed the study of the instability of a thin viscous sheet of fluid flowing through an inviscid vapor phase. This problem has direct application in the understanding of black liquor spraying. In order to accurately solve the sheet instability problem, it was necessary to accurately include the deviatoric normal stress in the liquid phase in the interfacial boundary condition arising from a normal stress balance. The driving force for sheet instability, variations in the vapor phase pressure must also be allowed. In this computational technique, vapor phase pressure variations are determined by solution of potential flow in the vapor phase coupled to the solution of the full Navier-Stokes equations in the liquid phase through both the continuity of normal velocity at the interface and the interfacial normal stress balance. The accuracy of this computational technique is demonstrated through solution of the lid-driven cavity problem for confined flows, the die-swell problem for free surface flows (with and without surface tension), and the stability of a thin viscous sheet flowing through a stagnant, inviscid vapor phase. Accurate solution of these test problems indicates that the new features of this computational technique work properly. Additional

Finite-dimensional dynamics and chaos in fluid flows

Abstract: We present a discussion of the role of finite-dimensional dynamics and chaos in interpreting nonlinear fluid mechanical motion The discussion will be restricted to two examples of fluid flows which have been studied by the author and which appear to be understandable in terms of ideas based in modern thinking in dynamical systems The specific examples we have chosen are the flow between concentric rotating cylinders commonly called the Taylor-Couette problem and the flow through a nominally two dimensional sudden symmetric expansion The first of these is a so called ‘closed flow’ problem and the second is an example of an ‘open flow’ where disturbances can grow as they are carried down stream The aim of the present article is to focus attention on the practicalities of applying the abstract concepts of finite-dimensional dynamics to the experimental study of fluid flows We will show how a careful consideration of the important symmetries of these problems can lead to the uncovering of structurally stable local organising centres for the global low-dimensional dynamical behaviour

On Eulerian and Lagrangian representation of steady incompressible fluid flow

Abstract: FOR THE description of fluid flow there are, in principle, two approaches, the Eulerian approach and the Lagrangian approach. The first one describes the flow of its velocity u = (u,(x), v,(x), uJx)) = u(x) in every point x = (xi, x2, x3) of the domain G containing the fluid. The second one uses the trajectory x = (xi(t), x2(t), x3(t)) = x(t) = X(t, x0) of a single particle of fluid, which at initial time t = 0 is located at some point x0 E G. This second approach is of great importance for the numerical analysis and computation of fluid flow [l-4], while the first one has often also been used in connection with theoretical questions [5-81. In the present paper we consider the stationary motion of a viscous incompressible fluid in a bounded domain G c R3 with a sufficiently smooth boundary S. Because for steady flow the streamlines and the trajectories of the fluid particles coincide, both approaches mentioned above are correlated by the autonomous system of characteristic ordinary differential equations

Steady flow of a viscous incompressible fluid between two co-axial circular cylinders with suction and injection

Abstract: In the present paper an attempt has been made to study the steady flow of a viscous incompressible fluid between two co-axial circular cylinders with small outward and inward normal suction on the outer and inner cylinders respectively with the assumption that the pressure is uniform over a cross-section. The expressions for axial velocity, the volume of fluid flowing per unit time across a cross-section and components of stress at any point of the fluid are derived.