Showing papers on "Pressure gradient published in 1970"

FORTRAN program for calculating compressible laminar and turbulent boundary layers in arbitrary pressure gradients

Abstract: FORTRAN program for calculating compressible laminar and turbulent boundary layers in arbitrary pressure gradients

The flat plate boundary layer. Part 2. The effect of increasing thickness on stability

Abstract: Numerical analysis has been used to find the neutral stability curve for the flat plate boundary layer in zero pressure gradient when the main terms representing the growth of boundary-layer thickness are either included or excluded. The boundary layer is found to be slightly less stable when the extra terms are included. The calculations give a critical Reynolds number of 500.

Convective Plumes in a Convective Field.

Abstract: The theory of isolated turbulent plumes given earlier is used to study a field of plumes. Each plume is immersed in the turbulent downdraft which comprises the return flow. The field of flow is specified by three parameters: the heat flux into the atmosphere at the surface, the depth of the convecting layer, and the intensity of turbulence at the surface (where turbulence is steadily generated by the wind) and where a plume element which leaves the surface returns there in a downdraft after a period of the order of 103 sec. The change in air properties during this period is of the essence of the problem. Since the process is driven by the changing density resulting from heating, the equations describing the field must be time-dependent in this essential respect. Wind is neglected, and the horizontal pressure gradient assumed to he the same at all heights. The derived plume properties-size, temperature excess, upward velocity and turbulent intensity-are in agreement with observation. The formulati...

The influence of wall heat transfer on the expansion following a C-J detonation wave

Abstract: Numerous investigations have shown that the wave velocity of a self-sustaining detonation is less than the ideal Chapman-Jouguet (C-J) value and that the deficit increases with decreasing tube diameter. Moreover, in small diameter tubes, the pressure gradient in the expansion behind the wavefront is steeper than that predicted by isentropic relations. Estimates of these deviations from ideality by the nozzle model of Fay, based on a viscous boundary-layer displacement, only partly account for the observed values. Numerical integration by Skinner of the non-steady equations of motion of the burned gases, assuming the Reynolds' analogy to hold between friction and heat transfer, shows that a growing region behind the front becomes time-steady as the wave recedes from its plane of origin. This prediction is confirmed in the present work by gas velocity measurements. An approximate solution of the non-steady equation is derived that is valid near the front and which allows a simple criterion to be stated for the attainment of a steady profile. Wall heat transfer measurements are described using platinum resistance gauges coated with silicon monoxide to suppress the effect of ionization. Transfer rate measurements near the wavefront of oxy-hydrogen waves agree well with the calculations of Sichel and David for the situation obtaining near the C-J plane. The value of the friction coefficient derived from the heat transfer data is used to compute the pressure and gas velocity profiles; these profiles are found to be in satisfactory accord with the observational values.

Slip Point of Beds in Solid-Liquid Pipeline Flow

Abstract: In view of the relatively low mean velocities which give optimum efficiency for pipelines transporting granular solids, it is important to study the conditions for which stationary deposits occur in pipes. The limit of deposition is the slip point, at which the force driving the bed exceeds the coefficient of friction times the total normal force exerted by the bed grains against the pipe wall. Although the state of intergranular stress in the deposit is generally indeterminate, it is shown that near the slip point it is a reasonable assumption that the granular pressure at the periphery of the bed follows a hydrostatic distribution. Experimental verification of this assumption was obtained from two types of tests, one involving flow conditions in a recirculating system and the other the slipping of deposits in a tilting pipe. The relationship derived for the hydrostatic distribution of granular pressure shows that the pressure gradient at the slip point is directly proportional to the underwater weight per unit volume of bed, and increases with the angle subtended by the deposit.

A Boundary-Layer Theory for Transient Viscous Losses in Turbulent Flow

Abstract: A laminar boundary-layer model is proposed to account for viscous losses during the transient turbulent flow of a liquid in a tube. In this model, inviscid slug flow is assumed for the core and all viscous effects are assumed to occur in the boundary layer. The transient boundary-layer velocity distribution is determined as a function of a prescribed variation in core velocity and the associated pressure gradient. Both analytical and numerical solutions are presented. This transient flow information is used to calculate local and integrated energy dissipation rates which are then combined, with one-dimensional energy analyses. The result is a prediction of the decrease in pressure-wave magnitude due to viscous dissipation, and a comparison is made with experimental data for rapid flow extinction. Good agreement between the observed and predicted results is obtained.

Boundary-layer separation at a free streamline. Part 1. Two-dimensional flow

Abstract: The boundary-layer flow just upstream of the trailing edge of a flat plate is studied when a free streamline is attached to the edge. The separation at the edge occurs with an infinitely favourable pressure gradient and is characterized by a skin friction which is proportional to the inverse eighth power of the distance from the edge. The proportionality factor for the first-order term is independent of the upstream boundary-layer flow. The streamwise velocity profile at separation is non-analytic near the wall Y = 0, and starts with the term .

Summary of available information on Reynolds analogy for zero-pressure-gradient, compressible, turbulent-boundary-layer flow

Abstract: Mathematical analysis of Reynolds analogy for turbulent heat transfer, skin friction, and boundary layer flow in adiabatic conditions

On the non-linear stability of plane Couette flow

Abstract: Plane Couette flow is defined as the flow which takes place between two parallel planes in the case of no pressure gradient in the flow direction. When no disturbance occurs, the velocity will be a linear function of the vertical coordinate z.

The Effects of Secondary Flow on the Laminar Dispersion of an Injected Substance in a Curved Tube

Abstract: The numerical solution by McConalogue & Srivastava (I968) of Dean's simplified NavierStokes equations for the laminar flow of an inviscid fluid through a tube of circular crosssection of radius a, coiled in a circular arc of radius L, and valid for k in the range (16.6, 77.1), where i =Re 4(alL), Re theReynolds number, is compared with experiment, correlated to the asymptotic solutions for k > 100, and extended to study the convective axial dispersion of a substance injected into the tube. The variation of the calculated flux ratio agrees closely with White's (I929) measurements of the inverse quantity over the same range, and the field patterns for the upper end of the range establish the validity of the two basic assumptions of the asymptotic solutions. The original method is extended to calculate the mean axial velocity of a typical particle of the fluid and to present the statistical distribution of mean velocity over the particles of a substance injected as a thin disk uniformly over the cross section of the tube. These distributions are used to display the variation with k of the shape of indicator concentration-time curves. The expected effect of secondary flow, in producing a more uniform distribution of velocity over the fluid than in Poiseuille flow, is evident. The iterative Fourier-series solution of Dean's (I927) simplified Navier-Stokes equations for the laminar flow of an incompressible viscous fluid through a curved tube of circular cross-section given by McConalogue & Srivastava (I968) is extended in the present paper to calculate the effects of the secondary flow on the dispersion of a substance injected into the tube. As a preliminary to this extension, the validity of the numerical solution is tested, directly by comparing its results with experiment, and indirectly by relating its results to theoretical work for a higher range of the dimensionless parameter on which dynamic similarity is based. The numerical solution was made to depend on a single variable D, a non-dimensional pressure gradient defined by AV Se l ) ~~~~~~~~( 1) where a is the mean axial pressure gradient, a the radius of the tube, L the radius of curvature of its axis, ,a the viscosity and v the kinematic viscosity. Convergent solutions were obtained for D in the range (96, 605.72), a region intermediate between the ranges covered by the perturbation solution of Dean (I927, i92z8) and the asymptotic solutions of Barua (I963), and Mori & Nakayama (I965). The numerical solution starts at D = 96, the top of the range for which Dean's series solution is

Cerebrospinal fluid and cranial sinus pressures. Relationship in normal and hydrocephalic cats.

Abstract: PRESSURE has repeatedly been demonstrated to be an important factor in bulk absorption of cerebrospinal fluid (CSF). The dependence of absorption on pressure was shown to be linear above a critical threshold pressure and thereafter over a wide pressure range. 1-4 A similar, although quantitatively different, relationship was shown to exist in hydrocephalus. 5,6 Regardless of the route of absorption, be it through the arachnoid villi in the normal animal 7 or by an alternate transventricular pathway in hydrocephalus, 8,9 all CSF absorbed must ultimately find its way into the venous system. Consequently, the pressure instrumental in CSF absorption is actually the pressure gradient between the CSF and the venous systems. Furthermore, if venous pressure varies with CSF pressure, the change should also be linear but not parallel. The present work is a study of the pressure relationship between the CSF system and the venous system as reflected in

Application Of Zagarola/Smits Scaling InTurbulent Boundary Layers With PressureGradient

Abstract: The empirical velocity scale determined for zero pressure gradient turbulent boundary layers of Zagarola and Smits [1], t/oo(

Comparison of left atrial pressure and wedge pulmonary capillary pressure. Pressure gradients between left atrium and left ventricle.

Abstract: Simultaneous records of wedged pulmonary capillary pressure and left atrial pressure have been made in I2 patients. The pressure changes in the left atrium preceded those in the pulmonary capillary bed by o-o6 to O0I4 sec. This delay, together with the damping of the wedged pulmonary capillary pressure, may result in a false appearance of an end-diastolic gradient between the left atrium and the left ventricle if simultaneous wedged pulmonary capillary pressure and left ventricular tracings are compared.

Similar solutions of the attached and separated compressible laminar boundary layer with heat transfer and pressure gradient.

Abstract: : The development of governing equations and tabulation of similar solutions to the two-dimensional, laminar, compressible boundary layer with heat transfer are presented. Similar velocity and temperature profiles and global quantities such as displacement thickness, momentum thickness, form factor, etc., are presented for 116 pressure gradient-heat transfer combinations. Surface temperatures for these cases range from absolute zero (S(0) = - 1) to twice the free stream stagnation temperature (S(0) = + 1), while the streamwise pressure gradient varies from values corresponding to maximum reversed flow (beta=-0.36) to those of extremely accelerated flows (beta = 20). Results are presented at regular intervals of the parameters S(0) and beta, allowing for straight-forward comparisons between cases. Five decimal place accuracy is maintained for all results. (Author)

Classical diffusion of a plasma in toroidal systems.

Abstract: The author considers the effects of plasma rotation on classical diffusion in toroidal systems. Within the framework of the hydrodynamic description of a plasma it is shown that, if the pressure gradient is not too great (ρ/a Bθ/Bz, where ρ is the ion Larmor radius, a−1 = d ln p/dr, Bθ is the azimuthal field and Bz the longitudinal field), then there is only one direction in which the plasma column can rotate with a velocity of the order of the drift velocity and at the same time become negatively charged – the diffusion coefficients differing only by a numerical factor of the order of unity from those previously known. It is also shown that there occurs in the plasma a transverse electric field which is much stronger than the Pfirsch-Schluter field and the direction of which depends on the path length of the particles.

Structure of Wind and the Shearing Stress in the Planetary Boundary Layer

Abstract: Analysis of the “Leipzig Wind Profile” shows close agreement between the direction of the wind and of the shearing stress throughout the planetary boundary layer. A formulation is developed, based on this quasi-parallelism and a boundary condition at the top of the Ekman layer, to relate the pressure gradient, the wind structure and the shearing stress throughout the layer. The predicted relationships are found to agree well with the Leipzig observations.

Influence of stress interaction effects upon pore motion in solids.

Abstract: A computer oriented analysis was undertaken in an attempt to fix the sign and magnitude of the response of a pore to a stress field. The present work agrees very well with an analytical result of other authors for the interaction of two bubbles within a solid continuum and reasonably well with their approximate analytical result for the interaction between a bubble and a free surface. The interaction between a bubble and a clamped surface is obtained. Two bubbles will always attract as long as at least one contains some “uncompensated” pressure. Further, such a bubble will be attracted to a free surface and repelled from a clamped surface. An analytical solution to the problem of an equilibrium bubble placed in a linear uniaxial stress gradient indicates the bubble will move up the gradient, whether the gradient is produced by external tension or compression. This is compared with a previous result for a pressure gradient; the uniaxial stress gradient produces a force about 50% higher than that due to a pressure gradient. Finally, estimates are made for the magnitude of these forces under physically plausible conditions.

Separation solutions for the similar laminar boundary layer

Abstract: The complete spectrum of similar laminar boundary-layer solutions exhibiting separation, pressure gradient, and mass transfer (blowing or suction) have been obtained. The resulting map includes variation of pressure gradient parameter and heat-transfer parameter as functions of mass transfer rate and wall enthalpy ratio. The solutions range from the limiting Blasius blow-off to an identification of asymptotic suction solutions. These latter solutions are obtained analytically. Nomenclature a,b = curve fit constants c = constant of integration / = transformed stream function g = stagnation enthalpy ratio, hs/hse h = static enthalpy qw = wall heat-transfer rate r = radius s = transformed streamwise coordinate u = streamwise velocity v = normal velocity x = streamwise coordinate y = normal coordinate /? = pressure gradient parameter 5* = displacement thickness t\ = transformed normal coordinate 0 = momentum thickness BH = energy thickness K — characteristic of asymptotic solution

Wide‐Range Calibration System for Pressure Gradient Hydrophones

Abstract: A gradient hydrophone calibrator consists of a precisely made water‐filled tank, with ports to receive the hydrophones to be calibrated and the reference pressure hydrophones, which is set into axial oscillation with suitable drivers to develop a standing wave of sound in the water. An improved calibrator is described, which, by using a very rigid tank, covers a range of 3–2500 Hz. Measurements are simplified through use of electrical feedback, which maintains a constant pressure‐gradient versus frequency function. The applications and limitations of this system to the measurement of sensitivity, frequency response, and phase response of pressure‐gradient and pressure hydrophones, and for obtaining the polar patterns of gradient hydrophones, are described.

In Situ Vapor Pressure Measurement for Low Temperature Thermometry

Abstract: By use of a capacitance diaphragm manometer operated at low temperatures, it is possible to measure the vapor pressure of cryogenic liquids without the uncertainties introduced by thermomolecular pressure gradients (thermal transpiration). Since the zero of this manometer is more stable at low temperature than at room temperature, useful sensitivity is increased. Because of the increased sensitivity at low pressure as well as great convenience and simplicity, this technique appears to have wide application in precise vapor pressure thermometry and similar work.

Comments on “The Flow of Non-Newtonian Fluids under a Varying Pressure Gradient”

Abstract: Barnes, Townsend and Walters1 have communicated some results concerned with the pulsating flow of a non-Newtonian fluid through a pipe, in which it was shown that the mean pressure gradient along the pipe axis in pulsating flow conditions can be less than the constant gradient in conditions of steady flow, and it is suggested that this may be of industrial importance

Convective magnetohydrodynamic flow in a vertical channel.

Abstract: An analysis is presented for the combined forced and free convective magnetohydrodynamic flow in a vertical, finite rectangular channel that is subjected simultaneously to a pressure gradient and a temperature gradient. Exact solutions are found for electrically nonconducting channel walls and perfectly conducting walls. In particular, the case of heating from below is examined and discussed.