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RESEARCH PAPERS

J. Fluids Eng. 1984;106(4):367-373. doi:10.1115/1.3243132.

Rarefied gas flow through a circular orifice and short tubes has been investigated experimentally, and the conductance of the aperture has been calculated for Knudsen number between 2 × 10−4 and 50. The unsteady approach was adopted, in which the decay of pressure in an upstream chamber was measured as a function of time. For flow with high pressure ratio, empirical equations of the conductance are proposed as a function of Reynolds number, or Knudsen number, and length-to-diameter ratio of the apertures.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):374-379. doi:10.1115/1.3243133.

A one-dimensional, quasi-steady, model describing the motion of a pig moving in a gas pipeline is developed for the cases of a solid pig, which obstructs the cross section of the pipe, and one with a concentric hole through it. The resultant governing equations constitute a set of seven nonlinear differential equations. A numerical solution scheme, implemented by a computer program, is described. Results and discussion are presented for a set of typical cases.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):380-384. doi:10.1115/1.3243134.

A new class of Taylor-unstable waves, consisting of ring waves appearing at the interface of two fluids of differing densities within a around pipe when the interface is accelerated in the direction of the denser fluid, is considered. The analysis employs a generalized coordinate method introduced by Dienes [16]. The characteristic “bubble-spike” configuration is obtained, although the singularity corresponding to infinite spike tip velocity occurs at a later time than for the one-dimensional plane wave. In addition, it has been shown previously [19] that condensation of vapor at the interface produces negligible correction to the growth rate.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):385-389. doi:10.1115/1.3243135.

Experiments were conducted in a three-dimensional lid-driven cavity flow to study the effects of the end walls on the size of the downstream secondary eddy. The ratio of cavity depth to cavity width is 1:1. The span of the cavity was varied such that span-to-width ratios of 3:1, 2:1, and 1:1 were obtained. Flow visualization was accomplished by the thymol blue technique, and by rheoscopic liquid illuminated by laser-light sheets, for Reynolds numbers (based on lid speed and cavity width) between 1000 and 10,000. The results indicate that the corner vortices present at the end walls, in the region of the downstream secondary eddy, are a major influence on the size of this eddy. In addition, as the span of the cavity is reduced the size of the downstream secondary eddy at the symmetry plane becomes smaller with increasing Reynolds numbers, for Reynolds numbers greater than 2000.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):390-398. doi:10.1115/1.3243136.

A synthesis of observations of flow in a three-dimensional lid-driven cavity is presented through the use of flow visualization pictures and velocity and heat flux measurements. The ratio of the cavity depth to width used was 1:1 and the span to width ratio was 3:1. Flow visualization was accomplished using the thymol blue technique and by rheoscopic liquid illuminated by laser-light sheets. Velocity measurements were made using a two-component laser-Doppler-anemometer and the heat flux on the lower boundary of the cavity was measured using flush mounted sensors. The flow is three-dimensional and is weaker at the symmetry plane than that predicted by accurate two-dimensional numerical simulations. Local three-dimensional features, such as corner vortices in the end-wall regions and longitudinal Taylor-Görtler-like vortices, are significant influences on the flow. The flow is unsteady in the region of the downstream secondary eddy at higher Reynolds numbers (Re) and exhibits turbulent characteristics in this region at Re = 10,000.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):399-404. doi:10.1115/1.3243137.

This paper presents a new analysis of the jet stripping process, as used to control coating thicknesses in the paper, photographic and galvanizing industries, and demonstrates that the inclusion of a surface shear stress term, acting in conjunction with the pressure gradient on the coating, gives theoretical predictions of coating behavior quite different from those based on stripping which allows only for pressure gradient effect. An illustration is given of how jets operating close to, and further from, the strip during hot dip galvanizing have different effects on the molten coating even though the final coating mass might be the same. Measurements of coating mass, taken from galvanizing line trials, have shown good agreement with the revised theory.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):405-409. doi:10.1115/1.3243138.

The objective of the study was to examine experimentally the turbulent flow structure near a repeated-rib geometry rough-walled surface as a function of the ratio of roughness height to pipe radius (K/R), the ratio of spacing between the elements to roughness height (P/K), and the axial position with the rib cycle. The centerline axial flow velocity was found to vary sinusoidally in the axial direction within a rib cycle for P/K>10 for K/R = 0.1437 and P/K>13 for K/R = 0.100. The roughness effect on the mean velocity profiles was characterized using a logarithmic equation which utilized an error in origin and a roughness function that was a function of the error in origin. The equation was found to be valid for P/K values of 7 or less for K/R = 0.1437 and 13 for K/R = 0.1 geometries.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):410-417. doi:10.1115/1.3243139.

A numerical study is made of the characteristics of turbulent submerged axisymmetric incompressible jets impinging on a flat plate and flowing into an axisymmetric cavity. The purpose of the study is to obtain a better understanding of the behavior of a fluid jet used to cut solid materials. In the computations a hybrid finite difference method is used to solve the full Navier-Stokes equations for an incompressible submerged jet with the k ∼ ε turbulence model. All computed results are compared with experimental data reported in the literature. For the case of the jet impinging on a flat plate, the computations are made for nozzle-to-plate distances ranging from 2 to 40 nozzle diameters. For the jet flowing into an axisymmetric cavity, computations are made for cavity depths ranging from 0 to 60 nozzle diameters. The use of the k ∼ ε turbulence model results in good predictions of the velocity, pressure, and skin friction distributions. The near-wall models for the kinetic energy and turbulent shear stress give good predictions of the skin friction coefficients.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):418-424. doi:10.1115/1.3243140.

Measurements of fluctuating lift are reported from four fixed rectangular prisms and a fixed circular cylinder, for various intensities of turbulence in the oncoming stream. Variations of unsteady lift with intensity of small scale turbulence are similar to present (and previous) measured variations of mean drag or base pressure. Reasons are suggested for these trends. Observations are also reported of the maximum (resonant) RMS amplitude of two cylinders, one square and the other circular in cross section, free to move in the cross stream direction. Small scale free stream turbulence provided by the wake of a small upstream rod increased the resonant amplitude of motion in both cases, the greater increase (and subsequent decrease) occurring for the square section. Two possible explanations for these observations are advanced.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):425-429. doi:10.1115/1.3243141.

Although the concepts of various types of ejectors have been thoroughly discussed in the literature during the past sixty years, a rigorous sensitivity analysis of the ejector’s performance has never been presented. In the present work a sensitivity analysis method, based on the use of adjoint functions, is introduced and applied to the one-dimensional model of a supersonic ejector. The advantage of the proposed method over all other possible techniques is that a single computer run can provide the response function sensitivities with respect to all input parameters. The usefulness of the sensitivity coefficients in predicting the ejector’s performance and the uncertainty involved, as well as in the determination of manufacturing tolerances, is demonstrated and proven to be a powerful tool in the design.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):430-434. doi:10.1115/1.3243142.

A hydraulic collapse mechanism was incorporated into a recirculating pulsatile flow system to collapse an elastic branching tube in a controlled manner. Changes in volumetric flow rate into and out of the tube model as well as axial pressure drop were monitored during this process. It was found that the driven collapse of the tube acted as a pump, the effectiveness of which was dependent on upstream and downstream resistance. In addition, there was noted a difference in the volumetric flow curves representing fluid leaving the pre- and the post-collapsed model under the same inflow conditions.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):435-440. doi:10.1115/1.3243143.

In this research, the hydrodynamic behavior of two laterally interconnected channels with blockages in one of them has been studied experimentally. For blockages of different shapes and severities, the mass flow rates as well as the pressures in the channels upstream and downstream of the blockage were determined. The experiments were conducted on a test sections which consists of two-square channels separated by an intermediate plate with slots of different geometric parameters. Two types of blockages have been considered: plate and smooth. The shape of the smooth blockage was a cosine. In the region upstream of the blockage, the diversion cross-flow takes place over a relatively short distance. Downstream of the blockage, the recovery of the diverted flow by the blocked channel is a slow process and the rate of this recovery worsens with increasing blockage severity. For a given blockage rate, the diversion crossflow caused by a smooth blockage is smaller than that of a plate blockage.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):441-447. doi:10.1115/1.3243144.

In this research, the hydrodynamic behavior of two laterally interconnected channels with blockages in one of them has been studied experimentally. For blockages of different shapes and severities, the mass flow rates as well as the pressures in the channels upstream and downstream of the blockage were determined. The experiments were conducted on two square channels separated by an intermediate plate with slots of different geometric parameters. Two types of blockages have been considered: plate and smooth. The shape of the smooth blockage was a cosine. The experimental data on the mass flow rates and pressures in the channels have been compared with the predictions of the subchannel code COBRA-III-C. It is observed that COBRA-III-C may not be adequate to describe the hydrodynamic behavior of two-interconnected channels with plate type blockages much higher than 30 percent severity in one of the channels. The limit of applicability of the code in the case of smooth blockages can be safely extended up to 60 percent severity.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):448-451. doi:10.1115/1.3243145.

This paper presents a comparison of two solutions, a numerical and an analytic, to an idealized problem of frictionless transient gas flow driven by internal heating. The purpose of such a comparison is to provide a check on a general method for transient gas flow in pipelines with friction and heat transfer. The numerical solution to this problem is formulated based on the method of characteristics with specified time intervals. To avoid interpolation for integration along the characteristics, a multiplier is introduced to the acceleration term in the equation of motion. Favorable comparisons of pressure and density time histories are obtained.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):452-458. doi:10.1115/1.3243146.

A theoretical analysis of choking in steady, one-dimensional, nonequilibrium, wet steam flows is presented. It is shown that such a flow becomes choked when the vapor phase velocity attains the frozen speed of sound somewhere in the system. The upstream flow pattern cannot then be altered by small adjustments of the back pressure and the mass flow rate is close to, although not necessarily identical to, its maximum value. The equilibrium speed of sound has no physical relevance in such flows. In a choked converging nozzle the critical conditions always occur in the exit plane of the nozzle. In a converging-diverging nozzle, however, the shape of the diverging section influences the throat conditions and throughput. Comparison of the theory with the few experiments reported in the literature shows excellent agreement.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):459-464. doi:10.1115/1.3243147.

It is shown that air bubbles of a certain size may be used to measure the fluctuating pressure in a liquid jet. The conditions under which these bubbles accurately reflect the local static pressures are described in detail; the volume shape of the bubbles was determined by holography for a 3.17 mm jet and the change in volume is interpreted as a result of the fluctuating pressure. The experimental results revealed that at any one instant, a wide spectrum of static pressure fluctuation intensities exist in the jet. It was also found that the probability distribution of these intensities has a slightly skewed bell shape distribution and that the fluctuating static pressure peaked at a higher positive value than a negative one.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):466-475. doi:10.1115/1.3243150.

This paper deals with an investigation of a method which detects the generation of cloud cavitation by the measurement of cavitation noise. Cavitation noise consists of a pulse train with approximately 1 μs rise time and 10 μs duration and has almost ultrasonic characteristics. By utilizing these chracteristics, the pulses of cavitation noise were measured, and a chart of cumulative pulseheight frequency was obtained. On this chart, the noise pattern due to cloud cavitation on a propeller working in nonuniform flow was clearly distinguished from other cavitation patterns.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):477-485. doi:10.1115/1.3243153.

A quasi-steady, two-dimensional thermal hydraulic analysis of the two-phase region formed ahead of a quench front during reflooding of a slab or cylindrical core is carried out, and the results for slab geometry are compared with the experiment. It is shown that the two-phase level variation in the core is due to the transverse heat flux power profile, and is sensitive to the assumed pressure-drop boundary condition for the bundle, while the effects of crossflow and axial friction are small. Implicit expressions are given for predicting the quasi-steady two-phase level variation across slab and cylindrical cores.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):486-490. doi:10.1115/1.3243155.

The problem of the growth of a spherical isolated bubble in a superheated liquid has been extensively studied. However, very little work has been done for the case of a cloud of bubbles. The collective behavior of the bubbles departs considerably from that of a single isolated bubble, due to the cumulative modification of the pressure field from all other bubbles. This paper presents a theoretical study on bubble interaction in a superheated liquid during the growth stage. The solution is sought in terms of matched asymptotic expansions in powers of ε, the ratio between rb0 , a characteristic bubble radius and l0 , the interbubble distance. Numerical results show a significant inhibition of the bubble growth rate due to the presence of interacting bubbles. In addition, the temperature at the bubble wall decreases at a slower rate. Consequently, the overall heat exchange during the bubble growth is reduced.

Commentary by Dr. Valentin Fuster
J. Fluids Eng. 1984;106(4):491-495. doi:10.1115/1.3243156.

This paper presents some results obtained with the simulation of a submerged oscillating jet impacting on a solid wall. The oscillating jet which organizes into large vortical structures is simulated by the emission of vortex rings at a constant frequency. Outside of the cores of the rings the fluid is assumed to be inviscid and irrotational. The positions of the tori are obtained by combining for each torus its self-induced velocity with the velocity induced by all other rings and ring-images in the wall. The tangential velocities and the pressures in the fluid at the wall are then computed. The high shearing and suction forces found at the wall may explain the enhanced erosivity and cleaning action of oscillating jets.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster

ERRATA

TECHNICAL BRIEFS

J. Fluids Eng. 1984;106(4):496-497. doi:10.1115/1.3243157.
Abstract
Commentary by Dr. Valentin Fuster

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