bluuebunny/crossref_metadata_2025_split huggingface dataset:
An experiment to measure the recombination rate of oxygen
Authors: Wilson J. 
Published: March 2006

The feasibility of an experiment to measure the recombination rate of oxygen is examined using the ideal-dissociating-gas model. The experiment is to be performed in a shock tube, the shock-heated (and dissociated) gas being cooled by passing it through a Prandtl-Meyer expansion, and then allowed to recombine in a constant-area channel. At appropriate densities and shock Mach numbers it is found that recombination takes place in a distance suitable for a laboratory experiment.Using this technique, the recombination rate of oxygen has been measured at 2700 ˚K. To determine the recombination rate, the absorption of ultraviolet light at a wavelength of 2283 å measured 11 cm downstream of the expansion was compared with absorptions calculated for various values of the recombination rate constant.The measured value of the recombination rate constant of oxygen is in agreement with values calculated from dissociation rate measurements.
Convection in a saturated porous medium at large Rayleigh number or Peclet number
Authors: Wooding R. A. 
Published: March 2006

When the dimensions of a convective system in a saturated porous medium are sufficiently great, diffusion effects can be neglected except in regions where the gradients of fluid properties are very large. A boundary-layer theory is developed for vertical plane flows in such regions. In special cases, the theory is equivalent to that for laminar incompressible flow in a two-dimensional half-jet, or in a plane jet or round jet, for which similarity solutions are well known.A number of experiments have been performed using a Hele-Shaw cell immersed in water, with a source of potassium permanganate solution located between the plates. At very small values of the source strength, a flow analogous to that of a plane jet from a slit is obtained. The distance advanced by the jet front, or cap, is measured as a function of time, and the velocity is found to be nearly proportional to the velocity of the fluid on the axis of the steady jet behind the cap, as given by the similarity law of Schlichting and Bickley. At large values of the source strength, a two-dimensional ‘broad jet’ of homogeneous solution descending under gravity is produced; the shape of the flow region can be calculated with little error from potential theory, neglecting the effect of the mixing layers.A possible example of a mixing layer observed in a geothermal region is examined. The theoretical form of the temperature distribution is calculated numerically, taking into account the large viscosity variation with temperature and also the possibility of a large permeability variation. These effects are found to have less influence upon the solution than might have been expected. Quantitative values obtained for the physical parameters are consistent with other geophysical observations.
An experimental study of the instability of the laminar Ekman boundary layer
Authors: Faller Alan J. 
Published: March 2006

This study concerns the stability of the steady laminar boundary-layer flow of a homogeneous fluid which occurs in a rotating system when the relative flow is slow compared to the basic speed of rotation. Such a flow is called an Ekman boundary-layer flow after V. W. Ekman who considered the theory of such flows with application to the wind-induced drift of the surface waters of the ocean.Ekman flow was produced in a large cylindrical rotating tank by withdrawing water from the centre and introducing it at the rim. This created a steady-state symmetrical vortex in which the flow from the rim to the centre took place entirely in the shallow viscous boundary layer at the bottom. This boundary-layer flow became unstable above the critical Reynolds number$Re_c = vD|v = 125 \pm 5$wherevis the tangential speed of flow,$D = (v| \Omega)^{\frac {1}{2}}$is the characteristic depth of the boundary layer,vis the kinematic viscosity, and Ω is the basic speed of rotation. The initial instability was similar to that which occurs in the boundary layer on a rotating disk, having a banded form with a characteristic angle to the basic flow and with the band spacing proportional to the depth of the boundary layer.
On plane flow of a gas with finite electrical conductivity in a strong magnetic field
Authors: Cowley M. D. 
Published: March 2006

The principal object of study is plane flow over bodies with a sharp apex at Mach numbers greater than unity. The magnetic field is assumed to be uniform, rectilinear, and parallel to the undisturbed stream. Flow behaviour near the apex of a wedge is investigated by the method of characteristics. It is found that for small wedge angles an attached shock attenuates initially with distance from the apex, but for larger wedge angles the shock grows stronger.The structure of a slow magneto-gasdynamic shock is investigated for the case of strong magnetic field and small electrical conductivity. The streamlines are displaced within the shock although the initial and final flow directions are the same. An ordinary gasdynamic shock may occur on the upstream side of the transition. The shock structure theory gives a solution for the flow near the apex of a certain class of bodies.For the study of slow shock structure, it is shown that the transition is described by a curve in the (F, H)-plane. F is the sum of pressure and momentum flux in the direction of variation; H is the sum of enthalpy and kinetic energy due to the velocity component in the direction of variation. General properties of the (F, H)-plane are found for a gas whose equation of state obeys the conditions of Weyl (1949). Flow behaviour on the transition curve is then determined. The theory of the (F, H)-plane can be used in the study of other one-dimensional processes in magneto-gasdynamics.
On the flow of an elastico-viscous liquid in a curved pipe under a pressure gradient
Authors: Thomas R. H. , Walters K. 
Published: March 2006

Consideration is given to the flow of an idealized elastico-viscous liquid in a curved pipe under a pressure gradient. By using the series expansion method of Dean (1927, 1928) in powers of a/R where a is the radius of the pipe and R the radius of curvature of its ‘central line’, it is shown that the general nature of the motion is similar to that of the motion of a Newtonian viscous liquid, the liquid elements moving along the pipe in two sets of spirals separated by the central plane. However elasticity of the type considered could strongly affect the pitch of these spirals. To the approximation considered, the flow pattern of the elastico-viscous liquid depends only on the limiting (zero-shear-rate) viscosity η0 and the first moment, K0, of the distribution of relaxation times. The corresponding stress components involve also the second moment of this distribution.It is also shown that the presence of elasticity in the liquid increases the rate of discharge of the liquid.
On the motion of liquid in a spheroidal cavity of a precessing rigid body
Authors: Stewartson K. , Roberts P. H. 
Published: March 2006

The flow set up in an oblate cavity of a precessing rigid body is examined under the assumptions that the ellipticity of the spheroidal boundary of the fluid is large compared with Ω/ω and that the boundary-layer thickness is small compared with the deviations of the boundary from sphericity (ωis the angular velocity of the rigid body about the axis of symmetry,Ωis the angular velocity with which this axis precesses).The motion of the fluid is found by considering an initial-value problem in which the axis of rotation of the spheroid is impulsively moved at a timet= 0; before that time this axis is supposed to be fixed in space, the fluid and envelope turning about it as a solid body. The solution is divided into a steady motion and transients, and, by evaluating the effects of the viscous boundary layer, the transients are shown to decay with time. The steady motion which remains consists of a primary rigid-body rotation with the envelope, superimposed on which is a circulation with constant vorticity in planes perpendicular toω× (ω×Ω), the streamlines being similarly situated ellipses.The possible effects of the luni-solar precession on the fluid motions in the Earth's core are discussed.
A simplified theory of magnetohydrodynamic isotropic turbulence
Authors: Betchov R. 
Published: March 2006

The simplest case of turbulent motion in a conductive fluid is studied. The turbulence is assumed incompressible, isotropic, homogeneous, charge invariant and free of fourth-order cumulants. The emphasis is placed on certain integrals of the correlation functions such as kinetic and magnetic energy, voticity, and current. A system of non-linear ordinary differential equations is derived which governs these integral quantities Several cases are solved numerically, illustrating the decay of ordinary turbulence, the buildup of magnetic energy by a linear or a non-linear process, the buildup of kinetic energy, as well as the destruction of vorticity by Lorentz forces.In order to handle certain dissipative effects, a special hypothesis is introduced which seems to promote mathematical simplicity. In particular, it leads to a simple decay law very similar to the decay law of ordinary turbulence.
On boundary layers in two-dimensional flow with vorticity
Authors: Harper J. F. 
Published: March 2006

The starting-point for this paper is the suggestion (Batchelor 1956b) that the wake behind a bluff body in a uniform stream may consist principally of two eddies rotating in opposite directions. The fluid is assumed to be incompressible and in two-dimensional steady motion at a very high Reynolds number. Along the boundary between the eddies, a viscous layer must form. This layer is unusual in that merely the vorticity, and not the velocity itself, varies appreciably across it. It will be shown that such layers can be treated theoretically much more simply than the general case, because it is possible to linearize the equation of motion. They may, of course, exist in flows other than that past a bluff body.A discussion is also given of the flow near the rear stagnation point, where this boundary layer meets the body. It had been suggested that a large number of small eddies would have to exist there, but this seems not to be so.
End effects in falling-ball viscometry
Authors: Tanner R. I. 
Published: March 2006

A calculation taking into account the interaction of tube wall and ends with a falling sphere is presented, with a view to assessing the change in drag on the sphere due to the end proximity in practical viscometry. It is shown that when the sphere is more than one fall tube radius from the closed end, the extra drag resulting is less than 4·5 × 10−3of the Faxèn drag, and is therefore usually negligible.For smaller end-sphere distances the end-effect drag increases rapidly, reaching about 1·5 of the Faxèn drag when the sphere centre is 0·25 tube radius from the end. The drag curve lies substantially below that given by Ladenburg (1907). Satisfactory agreement with experiment is found. It is concluded that with the commonly used types of fall tubes, end effects due to a closed end and an open surface will not be detectable.
Electrical conductivity of low-pressure shock-ionized argon
Authors: Smy P. R. , Driver H. S. 
Published: March 2006

The electrical conductivity of shock-ionized argon produced in an electromagnetic shock tube of low attenuation has been measured at shock speeds of March 10–33, with initial pressures of 0·01–2·0 mm Hg. These measurements extend considerably the range of previous measurements performed with pressure-driven shock tubes. With the higher initial pressures or at the highest Mach numbers the measured conductivity is in good agreement with the previous measurements and with the Spitzer–Harm (1953) formula for the conductivity of a fully ionized gas. With the lower initial pressures (which have not previously been investigated) and at the lower March numbers the conductivity falls to less than half of the Spitzer-Harm value. Order-of-magnitude calculations show that diffusion of atoms, and heat conduction by the plasma atoms from the plasma to the shock-tube walls, can cause appreciable plasma cooling (and hence a reduction of the electrical conductivity) with the lowest initial pressures. This mechanism in conjunction with non-attainment of equilibrium ionization appears to explain the observed diminution in conductivity at the lowest pressures, but not the reduced conductivity at the medium pressures.Induced e.m.f. flow-velocity measurements indicate steady-flow conditions in the shock tube while photomultiplier measurements of the plasma radiation indicate that the column of shock-heated gas is 10–20 cm long; this latter figure is supported by the conductivity measurements. The fact that the length of the shock-heated gas column is not drastically shortened at low initial pressures in constrast to the work of Duff (1959), Roshko (1960) and Hooker (1961) is attributed to the fact that in this experiment both driver and driven gases are at high temperature.
Rough-wall boundary layers in adverse pressure gradients
Authors: Perry A. E. , Joubert P. N. 
Published: March 2006

Smooth- and rough-wall boundary layers and fully developed pipe and duct flow investigations are reviewed. It is shown that the effect of roughness on the flow away from the wall can be accounted for by using an equivalent viscosity νe. This viscosity is thought to depend only on the variables at the wall, such as shear stress τ0, fluid density ρ, viscosity μ and the roughness size and geometry and that the relationship between these variables is the same for both boundary layers and duct flow. However, experiments to date have been confined to the ‘rough régime’ and to boundary layers with a zero pressure gradient.Experiments were performed and the results show that the above finding can be extended to boundary layers with adverse pressure gradients in the rough régime.A general method for measuring the local boundary-layer characteristics, with roughness and pressure gradients present, is developed.
Turbulent mixing at the top of stratocumulus clouds
Authors: Turner J. S. , Yang I. K. 
Published: March 2006

The process of mixing at the top of a turbulent cloud layer contains a new feature which has not been considered in previous studies of mixing; evaporation of liquid water can cause density changes which may affect the dynamics. A model experiment has been devised to study this problem, using liquids whose density behaviour is non-linear to simulate evaporation.The existence of a moist, stable, turbulent region above cloudtop can be explained using the laboratory results, which suggest that this region can be regarded dynamically as part of the cloud. Comparison of the rates of mixing in the model experiments with and without ‘evaporation’ suggests that evaporation could cause a small decrease in the mixing rate for a given density difference, but the change would be negligible in practice. This result also sheds some light on the mechanism of mixing, in both the linear and non-linear cases.
Resonant oscillations in closed tubes
Authors: Chester W. 
Published: March 2006

An investigation is made of the disturbances produced in a closed, gas-filled tube by the oscillations of a piston at one end, when the piston oscillates at near resonant frequencies. Within a well-defined frequency band around each resonant frequency, shock waves appear in the solution; outside this interval the oscillations are continuous, but not purely sinusoidal.The solution includes the effects of compressive viscosity, and of shear viscosity in the boundary layer at the walls of the tube. For typical laboratory conditions the effect of compressive viscosity is found to be quite small (giving a shock thickness of the order of 10−4in.). The boundary layer effect can be more significant, though the most important modification required of the usual acoustic theory is found to arise from the non-linear terms.
A wake model for free-streamline flow theory Part 2. Cavity flows past obstacles of arbitrary profile
Authors: Wu T. Yao-Tsu Wu , Wang D. P. 
Published: March 2006

In Part 1 of this paper a free-streamline wake model was introduced to treat the fully and partially developed wake flow or cavity flow past an oblique flat plate. This theory is generalized here to investigate the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation number. Consideration is first given to the cavity flow past a polygonal obstacle whose wetted sides may be concave towards the flow and may also possess some gentle convex corners. The general case of curved walls is then obtained by a limiting process. The analysis in this general case leads to a set of two functional equations for which several methods of solution are developed and discussed.As a few typical examples the analysis is carried out in detail for the specific cases of wedges, two-step wedges, flapped hydrofoils, and inclined circular are plates. For these cases the present theory is found to be in good agreement with the experimental results available.
Correlation measurements in a non-frozen pattern of turbulence
Authors: Fisher M. J. , Davies P. O. A. L. 
Published: March 2006

The properties of a turbulent flow are often described in terms of velocity correlations in space, in time, and in space-time. In this paper the interpretation of velocity correlation measurements which are made in a region of highintensity turbulence is considered in some detail. Under these conditions it is shown that some account must be taken of the effects of both mean and fluctuating shear stresses which are continuously modifying the turbulent structure. For an almost frozen pattern, for example, in the turbulence behind a grid, the turbulent convection velocity is amost equal to the mean flow velocity, while the space correlation and auto-correlation of the velocity fluctuations are simply related through this velocity. In contrast to this, when the intensity is high, the convection velocity may differ considerably from the mean velocity, while it is shown that different turbulent spectral components appear to travel at different speeds. This means that the turbulent spectrum and the turbulent space scales are no longer simply related. For example, the high-frequency spectral components may be ascribed to both the high-velocity eddies and the small wave-number components acting together.Experimental results are presented which indicate the conditions under which the assumption of a frozen pattern leads to uncertainties in the subsequent interpretation of the measurements. The measurements also show that the observed difference between the mean and the convection velocity may be qualitatively explained in terms of the skewness of the velocity signals.
The drag of a compressible turbulent boundary layer on a smooth flat plate with and without heat transfer
Authors: Spalding D. B. , Chi S. W. 
Published: March 2006

The theoretical treatments given by earlier authors are classified, reviewed and where necessary extended; then the predictions of twenty of these theories are evaluated and compared with all available experimental data, the root-meansquare error being computed for each theory. The theory of van Driest-II gives the lowest root-mean-square error (11.0%).A new calculation procedure is developed from the postulate that a unique relation exists betweencfFcandRFRwherecfis the drag coefficient,Ris the Reynolds number, andFcandFRare functions of Mach number and temperature ratio alone. The experimental data are found to be too scanty for bothFcandFRto be deduced empirically, soFcis calculated by means of mixing-length theory andFRis found semi-empirically. Tables and charts of values ofFcandFRare presented for a wide range ofMGandTS/TG. When compared with all experimental data, the predictions of the new procedure give a root-mean-square error of 9.9%.
On the cellular patterns in thermal convection
Authors: Stuart J. T. 
Published: March 2006

In the theory of thermal convective instability between two horizontal planes there are many solutions that are periodic in the horizontal co-ordinates, while in experiment convection is observed to take place in cellular patterns. It is often assumed, or decided after insufficient argument, that the periodic solutions of the mathematical model ‘explain’ or correspond to these patterns, but a completely satisfactory discussion of this correspondence has not been given. Indeed, with certain mathematical solutions ambiguities arise as to what cell centres and cellular boundaries are. A detailed discussion has recently become especially necessary because attempts are being made to predict which particular cellular pattern will occur in given experimental conditions.In this paper the topic is studied afresh and the question is asked: what features, in the mathematical model, correspond to what an experimentalist observes in cellular convective motion? In answer a definition of a cell is formulated which relates certain surfaces in the flow field of the mathematical model to steady vertical cellular boundaries that are observed in experiment, and which shows where the cell centres lie. In particular the classical hexagonal cellular pattern, of the mathematical model, is shown to be the prototype pattern of what is experimentally observed. On the other hand the square and so called ‘rectangular’ cases of linearized theory are shown not to correspond truly to square and rectangular cells at all. The new formulation is especially relevant to theoretical work on the prediction of cell shape and direction of flow in cells, since precise knowledge of the shapes of the cellular boundaries and locations of cell centres is essential if predictions are to be compared with observation.
The flow in the mixing region of a jet
Authors: Kolpin Marc A. 
Published: March 2006

The object of this work was to investigate experimentally the structure of the early shear layer of high-speed jets and its relation to the mechanism of noise generation. Of special interest was the question of the existence of periodic fluctuations in the velocity field. The experimental investigation is divided in three parts.Optical observation of the jet flow by means of the shadowgraph technique.Measurement of mean Mach number and temperature profiles.Survey by means of hot-wire of the component of the fluctuating velocity field in the mean flow direction.The shadowgraphs show very interesting features of the breakdown process of free shear layers, but fail to show any propagation of strong acoustic disturbances in the near pressure-field.Mean profile measurements show that the flow field in the range 1 [les ]x/d[les ] 4 develops in a conical fashion, i.e. the mean profiles in Mach number and temperature can be expressed in terms of a single conical variable η = (2r–d)/2x. The fluctuating velocity field is described in terms of the intensity of turbulence, its spectral distribution, and two-point space-time correlation functions. Similarity laws are given for the power spectra and the space-time correlation functions. On the cylinderr= ½d, the convection speed of the turbulent field is different for the different eddy sizes, varying from the local mean speed for small eddies to ½Uexitfor the large eddies. Measurements of the angular correlation function are reported which show no correlation of the fluctuations across the jet diameter.