Showing papers on "Fluid dynamics published in 1978"

International thermodynamic tables of the fluid state. 5. Methane

Abstract: The major part of this book is concerned with the preparation of an equation of state from the available experimental data, and with the density integrals resulting from it, which form the various X/sub 2/(p,T). The only published equation of state that takes account of all the new data is that by Goodwin, which was modified. The two equations are discussed. The tables presented give the volume, entropy, enthalpy, isobaric heat capacity, compression factor, fugacity/pressure ratio, Joule-Thomson coefficient, ratio of the heat capacities and speed of sound as functions of pressure and temperature; and the pressure, entropy, internal energy and isochoric heat capacity as functions of density and temperature for the gas and liquid states from 0.025 MPa to 1000 MPa at temperatures from 95 K to 470 K, and from 0.025 MPa to 40 MPa, 470 K to 620 K. Zero pressure tables are given, as are tables of the properties of the fluid phases along the saturation curve and the melting curve. 15 figures, 10 tables. (DP)

Flow Through Screens

Abstract: Control of the velocity distribution of a fluid flow is a fundamental problem In engineering fluid mechanics. The possible consequences for the operation and efficiency of downstream components need no emphasis here. Ability to control the flow is also necessary in component testing where, for results to be meaningful, test conditions must reproduce the composite flow situation. A screen may be used in both these operational modes to remove or create time-mean velocity nonuniformities, change the flow direction, and reduce or increase the scale and intensity of turbulence in a controlled manner. A screen may be thought of as any distributed resistance that effects a change in flow direction and a reduction in pressure. Common examples of screens for aerodynamic applications are arrays of parallel rods, honeycombs, perforated plates, and wire-gauze screens. This review focusses on the wire-gauze screen, with brief consideration of other types of screen. A survey of the available literature on the topic of flow through screens divides roughly into three categories:

Some physical processes in the solar wind

Abstract: The ‘standard physics’ of the solar wind is reviewed, and arguments that this standard physics is inadequate are summarized. A variety of suggestions for modifying the physics of the solar wind are then reviewed, with emphasis on effects of MHD waves of solar origin and collisionless or instability-limited electron heat conduction. The basic effects of the modified physics are demonstrated in a two-fluid model of the solar wind flow. The predictions of this model are carefully compared with observations, and the need for further observations is emphasized. The review concludes with suggestions for future theoretical efforts.

Predictions of Heat and Mass Transfer in Open Channels

Abstract: The paper describes a three-dimensional model for calculating the distribution of velocity, temperature, and pollutant concentration in open channel flows, and a depth-averaged two-dimensional version for situations with insignificant stratification and secondary currents. Both models are restricted to parabolic flows where influences cannot be transmitted upstream. The turbulent stresses and heat/concentration fluxes appearing in these equations are determined from the so-called k-ϵ turbulence model that solves differential transport equations for the turbulence kinetic energy k and the rate of its dissipation ϵ. In the depth-averaged model, the bottom shear stress, surface heat flux and turbulence production due to bottom shear are accounted for by source/sink terms in the relevant equations. The 3D calculations compare favorably with available measurements. The 2D and 3D predictions agree well for high Froude numbers; for a Froude number of 5 they agree only for the rough bed, while for the smooth bed they start to deviate significantly at a Froude number of 10.

Uniqueness of Solutions to Hyperbolic Conservation Laws.

Abstract: : It is known that conservative systems of differential equations which result from continuum mechanics (e.g. the equations of shallow water waves, fluid dynamics, magneto-fluid dynamics and certain elasticity problems) do not have unique solutions. Thus the problem arises of proving that systems of this type have only one physically meaningful solution. This report shows that there exists at most one solution satisfying an entropy condition which generalizes the second law of thermodynamics.

Fluid Forces on Oscillating Cylinders

Abstract: The paper presents the results of an experimental and analytical investigation of the forced oscillations of a circular cylinder in uniform flow. The transverse force has been decomposed into two components and the appropriate force-transfer coefficients have been determined experimentally through the use of a Fourier averaging techinique. The results were then incorporated into the equation of motion to predict the dynamic responsee of elastically-mounted cylinders. The numerical predictions were found to be in good agreement with those obtained experimentally.

Incompletely parabolic problems in fluid dynamics

Abstract: Some partial differential equations encountered in physical applications are of incompletely parabolic type; the Navier–Stokes equations in fluid dynamics are a typical example. In this paper we analyze such systems; in particular we treat the mixed initial-boundary value problem. In many applications there is a small parameter $\varepsilon $ multiplying the coefficient for the highest derivative. The energy method is used to derive well-posed boundary conditions such that, when $\varepsilon $ tends to zero, the reduced problem is also well posed.

Characteristics, Stability, and Short-Wavelength Phenomena in Two-Phase Flow Equation Systems

Abstract: The occurrence and significance of complex characteristics in two-phase flow equation systems are clarified by a detailed analysis of separated two-phase flow between two parallel plates. The basic...

Characteristics and Stability Analyses of Transient One-Dimensional Two-Phase Flow Equations and Their Finite Difference Approximations

Abstract: Equation systems describing one-dimensional, transient, two-phase flow with separate continuity, momentum, and energy equations for each phase are classified by use of the method of characteristics...

A three-dimensional model of corotating streams in the solar wind. 1: Theoretical foundations

Abstract: The paper is concerned with the development of the theoretical and mathematical background pertinent to the study of steady, corotating solar wind structure in all three spatial dimensions. The dynamical evolution of the plasma in interplanetary space (defined as the region beyond roughly 35 Rs where the flow is supersonic) is approximately described by the nonlinear, single-fluid, polytropic magnetohydrodynamic or hydrodynamic equations. Efficient numerical techniques are outlined for solving this complex system of coupled, hyperbolic partial differential equations. The present formulation is inviscid and nonmagnetic, but the methods used allow for the potential inclusion of both features with only modest modifications. A simple, highly idealized hydrodynamic model stream is examined to illustrate the fundamental processes involved in the three-dimensional dynamics of stream evolution. It is found that spatial variations in the rotational stream interaction mechanism produce small nonradial flows on a global scale that lead to the transport of mass, energy, and momentum away from regions of relative compression and into regions of relative rarefaction. Comparison with simpler models demonstrates the essential nonlinear, multidimensional nature of the interplanetary dynamics.

The flow of hot saline solutions from vents in the sea floor; some implications for exhalative massive sulfide and other ore deposits

Abstract: A variety of fluid flow phenomena involving fluids with thermal and compositional variations are reviewed, first as they are observed in simple laboratory experiments and then as they may apply to the formation of sulfide deposits resulting from exhalation of hot saline solutions from vents in the sea floor. Of particular interest is the case where the effluent is both very salty and hot, so that the two properties have opposing effects on the density difference between the exhaled fluid and its surroundings. This can lead to a very nonlinear density behavior during mixing, which makes it possible for initially light fluid to become heavier than sea water and for an oscillating flow to develop. Even more important are the "double-diffusive" effects which can occur because of the different molecular diffusion rates of the two properties. An outflow can separate into two parts, a hot, less concentrated plume which rises and a warm concentrated flow which spreads as a bottom current away from the source, maintaining a sharp boundary with the overlying sea water as it does so. If the hot salty fluid is injected into a density gradient, a situation which is typical of the ocean, a stratified lateral transport of the lighter fraction can result. For the heavier fraction, the effect of the combined processes is to maintain a stable boundary between the sea water and an exhaled hydrothermal ore solution, which might thus flow with minimal mixing along the sea floor over large distances to a distant depression before dumping its contained metals. A continuing inflow of dense fluid into such a depression produces a stable stratification, so that in a steady state the outflow spilling over the edge of the depression would be at a lower temperature and salinity and higher or lower f (sub O 2 ) . This condition provides a mechanism for localizing precipitation of sulfides within a small restricted depression from very large volumes of ore solution. Evidence of density stratification in the Bushveld Complex suggests the importance of related phenomena in the formation of layered igneous complexes. Analogous behavior in porous media is also indicated.

Axisymmetric ideal MHD stellar wind flow

Abstract: The ideal MHD equations are reduced to a single equation under the assumption of axisymmetric flow. A variational principle from which the equation is derivable is given. The characteristics of the equation are briefly discussed. The equation is used to rederive the theorem of Gussenhoven and Carovillano.

Free convective heat transfer in a viscous incompressible fluid confined between a long vertical wavy wall and a parallel flat wall

Abstract: Analyses of fluid flow over a wavy wall are of interest because of their applications to the physical problems mentioned in § 1. The authors have therefore devoted their attention to the effect of waviness of one of the walls on the flow and heat-transfer characteristics of an incompressible viscous fluid confined between two long vertical walls and set in motion by a difference in the wall temperatures. The equations governing the fluid flow and heat transfer have been solved subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and a disturbance or perturbed part. To obtain the perturbed part of the solution use has been made of the long-wave approximation. The mean (zeroth-order) part of the solution has been found to be in good agreement with that of Ostrach (1952) after certain modifications resulting from the different non-dimensionalizations employed by Ostrach and the present authors respectively. The perturbed part of the solution is the contribution from the waviness of the wall. The zeroth-order, the first-order and the total solution of the problem have been evaluated numerically for several sets of values of the various parameters entering the problem. Certain qualitatively interesting properties of the flow and heat transfer, along with the changes in the fluid pressure on the wavy and flat wall, are recorded in §§ 5 and 6.

Volume flow measurement system

Abstract: An apparatus and method for direct measurement of the volume flow of fluids through a tube, using an interferometric transit time technique is disclosed. First and second transducers for producing and receiving waves which are capable of being modified by the flow of the fluid in the conduit are positioned so that the conduit is fully and evenly illuminated by the waves. The transducers are located with respect to the conduit so that there will be a component of fluid flow along the axis of the illuminating wave beam. Means are provided to first activate one transducer to transmit waves while the other is in a receive mode and thereafter to place the second transducer in a transmit mode while the first is switched to its receive mode. The received waves are converted to corresponding electric signals by the corresponding transducers, and these signals are periodically sampled and stored for comparison. The result of this comparison is an electric signal which is proportional to fluid flow and is to a high degree independent of flow profile, conduit geometry, and alignment of the conduit within the probe. The device is particularly useful in measuring the flow of blood through a vessel.

Heat transfer and fluid flow phenomena in electroslag refining

Abstract: A mathematical formulation has been developed to represent the electromagnetic force field, fluid flow and heat transfer in ESR units. In the formulation, allowance has been made for both electromagnetically driven flows and natural convection; furthermore, in considering heat transfer the effect of the moving droplets has been taken into account. The computed results have shown that the electromagnetic force field appears to be the more important driving force for fluid motion, although natural convection does affect the circulation pattern. The movement of the liquid droplets through the slag plays an important role in transporting thermal energy from the slag to the molten metal pool, although the droplets are unlikely to contribute appreciably to slag-metal mass transfer The for-formulation presented here enables the prediction of thermal and fluid flow phenomena in ESR units and may be used to calculate the electrode melting rates from first principles. While a detailed comparison has not yet been made between the predictions based on the model and actual plant scale measurements, it is thought that the theoretical predictions are consistent with the plant-scale data that are available.

Device for the intravenous or enteric infusion of liquids into the human body at a predetermined constant rate

Abstract: A portable device for accurately metering a liquid for intravenous or enteric infusion into a patient's body in which the pressure from a pressure source is utilized to pressurize the liquid and the pressurized liquid becomes the sole driving force to meter and to infuse the liquid into the body. The pressurized liquid is applied alternately to one of a pair of flexible liquid bladders the other one being connected to a discharge device, such as a tube, so that, as one liquid bladder is filled with pressurized liquid, the other bladder is emptied into the patient. The expanding liquid bladder and the contracting liquid bladder cooperate with a teeter totter type control which applies pressure to the contracting liquid bladder and is damped to control the rate of expansion and contraction. The position of the teeter totter controls the valving for applying pressurized fluid from one side to the opposite by alternatively selecting channels of fluid flow to each liquid bladder. The angular motion of the teeter totter is controlled by a pair of flexible damping bladders connected through an adjustable constant flow valve which is disposed on the side of the teeter totter opposite the liquid bladders.

Theory of turbulence in a homogeneous fluid induced by an oscillating grid

Abstract: A theoretical model of steady turbulence caused by an oscillating grid in a box of homogeneous fluid agrees fairly well with observations of root‐mean‐square velocity and integral length scale. In the unsteady case the depth of the turbulent layer increases as the square root of time.

A theory of mixing in a stably stratified fluid

Abstract: A theory is developed for turbulence in a stably stratified fluid, for example in the experiments of Rouse & Dodu and of Turner where there is no shear and the turbulence is induced by a source of energy near the lower boundary of the fluid. A growing mixed layer of thickness D appears in the lower portion of the fluid and is separated from the non-turbulent fluid above, in which the buoyancy gradient is given, by an interfacial layer of thickness h. The lower mixed layer has a very weak buoyancy gradient and the large buoyancy difference across the interfacial layer is Δb.As indicated by the experiments of Thompson & Turner and Hopfinger & Toly, and derived by the author in a recent paper, if u is the root-mean-square horizontal velocity and l is the integral length scale, the eddy viscosity ul is a constant in a homogeneous fluid agitated by a grid. When there is stratification, the theory indicates that the fluid motion is unaffected by buoyancy forces in the mixed layer, so that ul should again be constant in the lower portions of the mixed layer. Since l is proportional to distance, we may conveniently suppose that the source of the disturbances is at a level z = 0 where u is infinite in accordance with uz = K. Thus we may take K to be a fundamental parameter characterizing the turbulent energy source. Then z is distance above the plane of the virtual energy source. If the non-turbulent fluid has uniform buoyancy, DΔb = U2 may be shown to be constant. In general, whether constant or not, U may be taken to be a fundamental parameter expressing the stability. The quantity is the most fundamental of the several Richardson numbers that have been introduced in this problem because, with its use, ‘constants’ of proportionality do not depend on the molecular coefficients of viscosity or diffusion (for high Reynolds number turbulence) or on the geometry of the grid.The theory contains a number of results: .h ∼ D, as observed in several experiments.

Development of a predictive tool for in-cylinder gas motion in engines

Abstract: A method is described of calculating the flow, temperature, and turbulence fields in cylinder configurations typical of a direct-injection diesel engine. The method operates by solving numerically the Navier Stokes equations that govern the flow, together with additional equations representing the effects of turbulence. A general curvilinear-orthogonal grid that translates with the piston motion is used for the calculations in the complex-shaped piston bowl, while an expanding/contracting grid is used elsewhere. Predictions are presented showing the evolution of the velocity and turbulence fields during the compression and expansion phases of a motored engine cycle, for various shapes of axisymmetric piston bowl and various initial swirl levels. The method is capable of solving the conservation equations governing in-cylinder flow and heat transfer in typical diesel and stratified-charge configurations with swirl under monitoring conditions, but the accuracy of the solutions remains to be assessed. The presence of a bowl provokes, even in the absence of swirl, a complex flow pattern containing at least two strong vortices, one being formed during the approach to top dead center by the squish phenomenon and the other in the clearance gap by reverse squish during the initial descent of the piston. The evolution of the turbulence intensity distribution can be explained largely in terms of the flow behavior. Changes in piston bowl shape and swirl level may profoundly alter the flow structures.

Solar energy collector

Abstract: A solar energy collector is disclosed including a housing forming a receptacle across which a fluid to be heated can flow and which is divided into a pair of chambers in the direction of fluid flow by a heat exchanging mat including a layer formed partially from an absorbent material and partially from a material having capillarity so as to retain a liquid fed into the layer and cause heating of the liquid by radiation impinging into the receptacle of the housing. A fluid medium, such as air, can be passed through the chamber formed below the aforementioned heat exchange mat to pick up heat from the mat for distribution as desired.

Instability, transition to turbulence and predictability

Abstract: : Contained herein is a concise state-of-the-art review and perspective on the phenomenon of transition which constituted the Opening Address at the Fluid Dynamics Panel Symposium on Laminar-Turbulent Transition (AGARD-CP-224). Various instability mechanisms leading to transition are proposed and discussed. A valuable insight is provided based on existing experimental evidence and postulated flow structures. Critical questions are asked relating to the conceptual foundations on which much of the transitional effort is based. To enhance our understanding of the basic mechanisms and processes, detailed microscopic experiments are encouraged to increase the data base.