Qualitative Flow Patterns Research Articles

Fluid flow analysis in horizontal continuous casting tundish

Water model studies were carried out to analyze fluid flow characteristics in a horizontal continuous casting tundish. The effects of LSN (ladle submerged nozzle) and dams on the flow pattems in a tundish were investigated and casting speeds were also changed as experimental parameters. Dye injection experiments were made to observe qualitative flow patterns and mixing characteristics in a continuous flowing tundish. And quantitative analyses of RTD (residence time distribution) curves using tracer pulse injection were also made to calculate the dead volume fraction in the water model tundish under consideration. From the results it was found that flow modification devices with an open stream have little effect on the flow patterns in the tundish, whether the dam is installed or not. This was confirmed by the flow visualization method showing upward flow near falling stream driven by the buoyancy force caused by air entrapment during liquid falling. However when LSN was installed between a ladle and a tundish there was a great change in flow pattern and a bypassing flow that existed in bare tundish was decreased with the use of dams. Especially, dead volume fraction was decreased with the increase of dam height.

Numerical Simulations of Gas Flow Patterns Within a Tall-Form Spray Dryer

Numerical simulations of the air flow patterns within a small scale tall-form countercurrent spray dryer have been performed. The simulations were performed using CFX 4.3, a finite volume based, computational fluid dynamics package. This study represents the first application of the Very Large Eddy Simulation (VLES) approach to the simulation of spray dryers. They have been performed in order to gain a more detailed understanding of the flow patterns and their stability in this design of dryer, which is commonly used in countercurrent drying applications, such as the drying of detergents. Limited validation of the simulations was achieved through comparison against qualitative experimental flow pattern information. It was found that by altering the angle of the inlet air streams into the dryer, the nature of the flow within the dryer could be significantly altered. In the majority of the cases simulated, large transients developed in the flow, the nature of these transients being critically dependent on the inlet conditions. The existence of such transients would be detrimental to actual spray dryer performance, however the flow patterns can be stabilised by introducing a large amount of swirl into the chamber.

Propagation of Nonlinear Waves in a Spatially Nonuniform Gas-Liquid Medium

Specific features of the evolution of nonlinear pulse disturbances in a bubbly gas-liquid medium with periodic variation of the gas void fraction in the pulse propagation direction are studied. The effect of the period and amplitude of the void fraction nonuniformity on the propagation of a single pulse is analyzed both with and without account for heat transfer in the medium. It is demonstrated that taking the heat transfer into account has no impact on the qualitative flow pattern.

Boiling in a porous layer heated from below: effects of natural convection and a moving liquid/two-phase interface

Boiling and natural-convection processes in a horizontal, fluid-saturated porous layer are investigated. The layer is heated uniformly from below and is cooled from above. Volumetric cooling is also allowed. The thermodynamic structure consists of a liquid region overlying a two-phase region. Numerical techniques are used to solve the transient, two-dimensional equations in the liquid and two-phase regions, and at the phase-change interface. A parametric study is carried out in terms of the liquid-phase Rayleigh number (Ra) and the non-dimensional bottom heat flux (Qb). Three solution regimes are observed: conduction-dominated at low Ra, convection-dominated at intermediate Ra, and oscillatory convection at high Ra. In the convection-dominated regime, transitions to multiple cell patterns are observed as Qb is increased. Oscillatory convection appears to be triggered by asymmetric disturbances in the system. The effects of initial conditions and the stability of the solutions to perturbations are also investigated. The heat transfer correlations and qualitative flow patterns are in agreement with experiments.

Internal Standing Waves in a Cylindrical Vessel and Their Near-Wall Features

This paper describes numerical and experimental investigations on internal standing waves occurring in a cylindrical vessel and their near-wall behavior in the vicinity of an adiabatic cylinder located at the center of the vessel. A numerical prediction method was developed with a low-Reynolds-number turbulence model to stimulate the occurrence of the internal standing waves and their near-wall features. These features are characterized by the attenuation and phase shifts in temperature fluctuations as observed in the present experiments. The measured results were well predicted by the numerical simulation in terms of certain statistical values as well as qualitative internal wave motions and flow patterns.

Shock interference prediction using direct simulation Monte Carlo

The shock interaction produced when an incident shock impinges on an inlet cowl lip is investigated for a cowl lip radius of 0.1 in. and flight conditions of Mach 15 and 35-km altitude. This problem is of interest in the design of hypersonic flight vehicles because the interference heating at the cowl lip surface from such a shock interaction is expected to be very high and the design of adequate thermal protection in this region will be challenging. Noncontinuum effects may be significant at this combination of altitude and small dimensions. If this is so, a computational solution based on the Navier-Stokes equations could significantly overpredict the surface heating on the cowl lip. Therefore, a kinetic theory solution technique, direct simulation Monte Carlo (DSMC), is used to predict the flowfield and surface heating. The details of modeling this problem and some preliminary results are presented. The same qualitative flow patterns are seen with DSMC and a continuum solution of the shock interference case, but the peak heating predicted with DSMC is somewhat lower.

33 流体中の微小粒子の挙動

Tracer methods have been frequently applied to know flow patterns in flow visualization technique.Recently, they have been applied not only to know qualitative flow patterns, but also to know some flow quantities through the measurements of tracer velocities under the remarkable development of computers and image processing techniques in a decade. In this stage, it becomes important to know the response of a tracer particle to rapid change of flow velocity like as in turbulent flow.The step response of a tracer particle is discussed analytically in this paper, by the use of Tchen's equation of motion, including the Basset history term which has the important role in high rate acceleration.

COMBINED BUOYANCY, SURFACE TENSION FLOW IN LIQUID METALS

The characteristics of combined buoyancy and thermocapillary flow for liquid metals in a rectangular cavity have been studied numerically. Results show that, for augmenting buoyancy and surface tension forces, qualitative flow patterns and isotherms are unchanged, but enhanced fluid velocities and heat transfer rates occur. In contrast, for counteracting buoyancy and surface tension forces, three different flow regimes are identified, with minimum heat transfer rates occurring when buoyancy and surface tension forces are of equal importance. The flow and temperature fields, as well as heat transfer rates, have been studied for aspect ratios of 0.5, 1.0, and 2.0.

Flow in an Open Tank With a Free Surface Driven by the Spinning Bottom

An investigation is made of flows of a viscous incompressible fluid inside a circular cylindrical tank. The flow is driven by the spinning bottom endwall disk of the tank. Numerical solutions of the Navier-Stokes equations were obtained over a range of rotational Reynolds number and of aspect ratio (cylinder height/radius) using two kinds of boundary condition at the top: a closed tank with a rigid lid and an open tank with a free surface. We provide descriptions of flow details for these two boundary conditions at the top. For small aspect ratios, the nature of the azimuthal flow is distinctly different depending on the type of the top boundary condition, i.e., a Couette flow under a rigid lid and a solid-body rotation under a free surface. These qualitative flow patterns are insensitive to the Reynolds number. For flows with a finite aspect ratio and at small Reynolds numbers, the change in the top boundary condition has little impact on the flow. For flows with a finite aspect ratio and at large Reynolds numbers, the prevailing flow patterns are of boundary layer-type. At a given vertical level, the angular velocity attains a larger value under a free surface than under a rigid lid.

Hydrodynamical interaction of two emulsion droplets at small separations

The fluid's motion inside emulsion droplets is analysed when they mutually approach along their common axis and a thin liquid film is formed outside. A qualitative flow pattern is presented. Two particular cases are treated — a creeping motion and a boundary layer flow inside the droplets. Estimates are made for the tangential velocity at the droplet/film interface, for the drag force and for the energy dissipated in the respective phases.

The Three-Shock Confluence Problem for Normally Impinging, Overexpanded Jets

SummaryIn this paper, a systematic study of the triple shock confluence point is presented for the case of an overexpanded jet which impinges on a perpendicular flat plate at small displacements from the nozzle. The jet is uniform upstream of the free jet shock wave. Non-homentropic effects are taken into account and lead to modifications to the accepted flow patterns at a triple point for the case of strong incident shock waves. Where more than one thermodynamically possible solution to the triple point equations exists, the alternative solutions are re-examined, taking non-homentropic effects into consideration. Some discussion of the possibility of infinite shock curvatures is also included. Qualitative flow patterns of the impinging flow are constructed, based on the triple point solutions and the known boundary conditions. The interesting cases where the tail shock flow is supersonic are given particular attention and two possible flow patterns are distinguished. Finally, some experimental evidence in the form of schlieren pictures is presented. Although not conclusive, this evidence supports the theory.

Behavior of polymer melts in rotary instruments of the plane-plane and cone-plane type

The qualitative flow pattern of polyethylene melts in rotary instruments of the plane—plane and cone—plane type is examined. It is shown experimentally that in these instruments the flow lines are Archimedes spirals, which indicates the presence of radial mass transport.