bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Boundary Layers With Sudden Transverse Strain
Authors: Gibson M. M. , Younis B. A.
Published: October 2009

Modifications to a Reynolds stress closure are proposed in which the weighting of the two components of the pressure-strain correlation is adjusted: the turbulence part is increased to conform with measured rates of return to isotropy and the contribution from the mean-strain part is reduced. Consequential changes are then needed in the other closure assumptions. Their effect is to make the model more generally applicable and to improve predictions of turbulent flows in complex strain fields. The revised model is tested here against the measured response of axisymmetric boundary layers to suddenly imposed rotation. The wall region of this flow is resolved by means of wall functions where it is assumed that the directions of the shear stress and the mean-strain rate are coincident.
Improvement of Unstable Characteristics of an Axial Flow Fan by Air-Separator Equipment
Authors: Miyake Y. , Inaba T. , Kato T.
Published: October 2009

The authors’ previous papers demonstrated that an air-separator is the most effective equipment among various different types for the improvement of unstable characteristics of an axial-flow rotor. Further experiments revealed that this equipment could eliminate the unstable characteristics thoroughly even for a build which originally accompanied a heavy rotating stall. This paper describes the geometric conditions to realize this and discusses its performance mechanism on the basis of the experiments showing the discharge distribution of the bleeding flow from the blade tip to separator passage as well as the pressure distribution in a blade passage at the tip section of the rotor. It is suggested that the equipment is equally useful at any stage of a multistage rotor.
Fluid Motion Within the Cylinder of Internal Combustion Engines—The 1986 Freeman Scholar Lecture
Authors: Heywood John B.
Published: October 2009

The flow field within the cylinder of internal combustion engines is the most important factor controlling the combustion process. Thus it has a major impact on engine operation. This paper reviews those aspects of gas motion into, within, and out of the engine cylinder that govern the combustion characteristics and breathing capabilities of spark-ignition engines and compression-ignition or diesel engines. Necessary background information on reciprocating engine operating cycles, the primary effect of piston motion and the spark-ignition and diesel engine combustion processes is first summarized. Then the characteristics of flow through inlet and exhaust valves in four-stroke cycle engines, and through ports in the cylinder liner in two-stroke cycle engines are reviewed. These flows govern the airflow through the engine, and set up the in-cylinder flow that controls the subsequent combustion process. The essential features of common in-cylinder flows—the large scale rotating flows set up by the conical intake jet, the creation and development of swirl about the cylinder axis, the flows produced during compression due to combustion chamber shape called squish, flow during the combustion process, and two-stroke scavenging flows—are then described. The turbulence characteristics of these flows are then defined and discussed. Finally, flow phenomena which occur near the walls, which are important to heat transfer and hydrocarbon emissions phenomena, are reviewed. The primary emphasis is on developing insight regarding these important flow phemomena which occur within the cylinder. To this end, results from many different research techniques—experimental and computational, established and new—have been used as resources. It is the rapidly increasing convergence of engine flow information from these many sources that make this an exciting topic with promise of significant practical contributions.
Calculation of Three-Dimensional Boundary Layers on Rotating Turbine Blades
Authors: Anderson O. L.
Published: October 2009

An assessment has been made of the applicability of a three-dimensional boundary-layer analysis to the calculation of heat transfer and streamline flow patterns on the surfaces of both stationary and rotating turbine passages. In support of this effort, an analysis has been developed to calculate a general nonorthogonal surface coordinate system for arbitrary three-dimensional surfaces and also to calculate the boundary-layer edge conditions for compressible flow using the surface Euler equations and experimental pressure distributions. Using available experimental data to calibrate the method, calculations are presented for the endwall, and suction surfaces of a stationary cascade and for the pressure surface of a rotating turbine blade. The results strongly indicate that the three-dimensional boundary-layer analysis can give good predictions of the flow field and heat transfer on the pressure, suction, and endwall surfaces in a gas turbine passage.
Suppression of Sheet Cavitation Inception by Water Discharge Through Slit
Authors: Kato Hiroharu , Yamaguchi Hajime , Okada Shinzo , Kikuchi Kohei , Miyanaga Masaru
Published: October 2009

This paper studies experimentally the suppression effect of water discharge on incipient and developed sheet cavitation on a hemispherical headform. The water is discharged tangentially from a slit upstream of a cavitating region into the boundary layer on the headform. Increasing the discharge rate, the length of the sheet cavity becomes shorter and then the cavity is suppressed completely. Flow visualization test shows the generation of wavy motion in the boundary layer which disturbs the separated zone, resulting in disappearance of the sheet cavitation.
Incompressible Laminar Flow Past a Transversely Vibrating Cylinder
Authors: Chilukuri R.
Published: October 2009

An implicit finite difference scheme in primitive variables is used for analysis of unsteady, laminar flow past transversely vibrating cylinders. Predictions of flow past an impulsively started cylinder and of vortex shedding from a stationary cylinder agree well with experimental data. Calculations of flow past a transversely vibrating cylinder were within the range of experimental scatter only for small vibration amplitudes. Several experimentally observed phenomena such as drag amplification and reduction in excitation lift coefficient at large vibration amplitudes were numerically predicted.
Numerical Model for Fluid Spin-Up From Rest in a Partially Filled Cylinder
Authors: Homicz G. F. , Gerber N.
Published: October 2009

A numerical investigation is presented for the axisymmetric spin-up of fluid in a partially filled cylindrical cavity. It is an extension of earlier analyses to those cases where the liquid free surface intersects one or both endwalls. Previous models of the laminar Ekman layer pumping are modified heuristically for situations where the layer(s) no longer covers the entire wall. Numerical results for a range of Reynolds number, Froude number, and fill ratio have been obtained. They clearly demonstrae that it is the bottom wall Ekman layer which is primarily responsible for spin-up.
Studies of the Configuration and Performance of Annular Type Jet Pumps
Authors: Shimizu Yukimaru , Nakamura Shogo , Kuzuhara Sadao , Kurata Shigemitsu
Published: October 2009

In this paper, we investigated experimentally the relation between configuration and performance of the annular type jet pump and compared it with that of the central jet type. Twenty-five different kinds of pumps were used in the experiments. These pumps reached a maximum efficiency of thirty-six percent. This corresponds with that of the conventional central jet type pump. We also studied the effect of the swirl component in the driving jet, and compared it with the result without swirl component.
Study of Fully Developed Incompressible Flow in Curved Ducts, Using a Multi-Grid Technique
Authors: Ghia K. N. , Ghia U. , Shin C. T.
Published: October 2009

Fully developed flows inside curved ducts of rectangular as well as polar cross sections have been analyzed using the Navier-Stokes equations in terms of the axial velocity and vorticity and the cross-flow stream function. Numerical solutions of the three second-order coupled elliptic partial differential equations governing this flow have been obtained using efficient numerical schemes. For curved-duct flows, the similarity parameter of significance is the Dean number K, rather than the Reynolds number Re. Results have been obtained for curved ducts with square cross sections for K up to 900 which, in the present study, corresponds to Re = 9,000 for this internal flow configuration. The fine-grid calculations show that, for square cross-section ducts, Dean’s instability occurs at K ≈ 125 and, further, that this phenomenon does not disappear even for K = 900. In ducts of polar cross sections, which are geometrically more representative of turbomachinery cascade passages, the phenomenon of Dean’s instability is not seen to occur for K up to 600.
Entrainment by Turbulent Jets Issuing From Sharp-Edged Inlet Round Nozzles
Authors: Trabold T. A. , Esen E. B. , Obot N. T.
Published: October 2009

Experiments were carried out to determine entrainment rates by turbulent air jets generated with square-edged inlet round nozzles. A parametric study was made which included the effects of Reynolds number, nozzle length, partial confinement and geometry of the jet plenum chamber. Measurements were made for the region extending from the nozzle exit to 24 jet hole diameters downstream. There is a large difference in the rate of fluid entrainment between jets generated with relatively short nozzles and those discharged through long tubes.
Steady Flow Structures and Pressure Drops in Wavy-Walled Tubes
Authors: Ralph M. E.
Published: October 2009

Solutions of the Navier-Stokes equations for steady axisymmetric flows in tubes with sinusoidal walls were obtained numerically, for Reynolds numbers (based on the tube radius and mean velocity at a constriction) up to 500, and for varying depth and wavelength of the wall perturbations. Results for the highest Reynolds numbers showed features suggestive of the boundary layer theory of Smith [23]. In the other Reynolds number limit, it has been found that creeping flow solutions can exhibit flow reversal if the perturbation depth is large enough. Experimentally measured pressure drops for a particular tube geometry were in agreement with computed predictions up to a Reynolds number of about 300, where transitional effects began to disturb the experiments. The dimensionless mean pressure gradient was found to decrease with increasing Reynolds number, although the rate of decrease was less rapid than in a straight-walled tube. Numerical results showed that the mean pressure gradient decreases as both the perturbation wavelength and depth increase, with the higher Reynolds number flows tending to be more influenced by the wavelength and the lower Reynolds number flows more affected by the depth.
Resistance to the Flow of Fluids Through Simple and Complex Porous Media Whose Matrices Are Composed of Randomly Packed Spheres
Authors: Fand R. M. , Kim B. Y. K. , Lam A. C. C. , Phan R. T.
Published: October 2009

Experimental data relating to the flow of fluids through simple and complex porous media whose matrices are composed of randomly packed spheres have been obtained. In this context the term “simple” refers to porous media whose matrices are composed of spheres of uniform diameter, while “complex” refers to matrices composed of spheres having different diameters. It was found that Darcy’s law is valid for simple media within a range of the Reynolds number, Re, whose upper bound is 2.3. The upper bounds of Darcy flow for complex media were found to be consistent with this value. It is shown that the resistance to flow in the Darcy regime can be characterized by taking the Kozeny-Carman constant equal to 5.34 if the characteristic dimension is taken equal to the weighted harmonic mean diameter of the spheres that comprise the matrix. Forchheimer’s equation was found to be valid for simple media within the range 5 ≤ Re ≤ 80. The corresponding bounds for complex media were found to be consistent with this range. It is shown that the resistance to flow in the Forchheimer regime for both simple and complex media can be characterized by adopting the following values of the Ergun constants: A = 182 and B = 1.92. Finally, it is shown that fully developed turbulent flow exists when Re > 120 and that the resistance to flow in the turbulent regime can be calculated using Forchheimer’s equation by adopting the following values of the Ergun constants: A′ = 225 and B′ = 1.61. A simple method for characterizing the behavior of porous media in the transition regions between Darcy and Forchheimer and between Forchheimer and turbulent flow is presented.
Numerical Simulation of Fluid-Particle Flows: Geothermal Drilling Applications
Authors: Givler R. C. , Mikatarian R. R.
Published: October 2009

In order to understand how a particulate plug may evolve within the flow of an essentially homogeneous suspension, we have developed a fluid-particle flow model. This theoretical model is based upon a monodisperse collection of rigid, spherical particles suspended in an incompressible, Newtonian liquid. Balance equations of mass and momentum are given for each phase within the context of a continuum mixture theory. The interactions between the phases are dominated by interfacial drag forces and unequilibrated pressure forces. The pressure associated with the solid particles is given by a phenomenological model based upon the flow dynamics. Of primary concern is the calculation of solid particle concentrations within a flow field to indicate the initiation of a particulate plug.
Measurements of Primary and Secondary Flows in an Industrial Forward-Curved Centrifugal Fan
Authors: Cau G. , Mandas N. , Manfrida G. , Nurzia F.
Published: October 2009

An industrial-type centrifugal-flow fan was instrumented and tested in order to obtain a fully detailed relative flow pattern at impeller discharge. Testing entailed investigation of both primary flows (jet-wake pattern and presence of return flows) and secondary flows (due to streamwise vorticity either from meridional curvature or rotation effects). In addition to conventional probing, a crossed hot-wire probe was employed in the tests. Ensemble-averaging the hot-wire signals made it possible to obtain the three-dimensional phase-averaged relative flow pattern at discharge by means of double positioning of the probe. Results show secondary-flow effects of appreciable magnitude interacting with primary flows (e.g., return flow in the hub region and variations in vortex structure and wake position with variations in flowrate).
A Study of Performance Improvement for High Specific Speed Centrifugal Compressors by Using Diffusers With Half Guide Vanes
Authors: Yoshinaga Y. , Kaneki T. , Kobayashi H. , Hoshino M.
Published: October 2009

The experimental results from eighteen different centrifugal compressor stages showed that the pressure recovery of vaneless diffusers for high specific speed compressors was extremely low compared with the value expected by an ideal two-dimensional analysis. Consequently a new type of diffuser with half guide vanes on the shroud side wall was proposed. The pressure recovery of this diffuser at distorted inlet flow was considerably improved by the half guide vanes. The optimum height of the vanes was a little less than one half of the diffuser width. Measurements of the velocity distribution in the diffusers using Pitot tubes and a laser-two-focus velocimeter, clearly showed that the small height guide vanes gave a uniform flow in the axial direction and improved the pressure recovery of the diffuser.
Valve and In-Cylinder Flow Generated by a Helical Port in a Production Diesel Engine
Authors: Arcoumanis C. , Vafidis C. , Whitelaw J. H.
Published: October 2009

The flow generated by the helical port of a production Diesel engine has been investigated by laser Doppler anemometry under steady flow and operating conditions at ∼ 900 rpm and compression ratio of 8. The flow around the valve periphery was found to be non-uniform with the axial velocity distribution being more sensitive to valve lift. The in-cylinder swirl distribution at inlet valve closure exhibited an axial stratification in the disc-chamber while turbulence intensity remained constant in the clearance volume during the rest of the compression stroke with levels of 0.5 vp and a minimum of about 0.4 vp at top-dead-center following a rapid decay at θ=340°.
Unsteady Viscous Flow Between Parallel Disks With a Time-Varying Gap Width and a Central Fluid Source
Authors: Ishizawa S. , Watanabe Tooru , Takahashi Koji
Published: October 2009

A theoretical analysis is presented for the unsteady laminar flow of an incompressible fluid between parallel disks with a time-varying gap width and a central fluid source of constant flow rate. New series solutions to the Navier-Stokes equations are obtained, on the basis of asymptotic series expansion in the radial direction and a new theory of “multifold series expansion” with respect to the time variable. The solutions cover the general case of arbitrarily time-varying gap width. Moreover, it can describe precisely the complicated non-linear interaction between the two coexisting flows due to the gap-width variation and to the central fluid source. Experiments were carried out for the case of sinusoidally oscillating gap-width variation, and it has been confirmed that the present solutions agree well with the experiments, even in severe cases that an approximate superposition theory neglecting the aforementioned interaction effect produces a remarkable error.
The Trailing Edge of a Pitching Airfoil at High Reduced Frequencies
Authors: Poling D. R. , Telionis D. P.
Published: October 2009

Trailing edge flows are visualized for a pitching airfoil. The validity of the quasi-steady and an extension to an unsteady Kutta condition, namely the Giesing-Maskell condition are examined. A new dynamic similarity parameter is proposed. Earlier work and the present results are re-evaluated in terms of this parameter. A range is identified in which no Kutta-type condition may apply.
Fluid Excitation Forces Acting on a Square Tube Array
Authors: Chen S. S. , Jendrzejczyk J. A.
Published: October 2009

Fluid forces acting on a tube array are important in the assessment of vibration of system components consisting of multiple circular cylinders. This paper presents test results for a square tube array with the pitch-to-diameter ratio of 1.75 subject to turbulent flow. The fluctuating drag and lift forces are measured as a function of Reynolds number, incoming flow conditions, and tube location in an array.
Review—Turbomachinery Performance Deterioration Exposed to Solid Particulates Environment
Authors: Tabakoff W.
Published: October 2009

The objective of this paper is to review experimental and analytical investigations concerning the effect of the presence of solid particles on the performance of turbomachines. Experimental data on the effect of solid particles on turbine and compressor performance are examined. Some basic data have been reinterpreted to provide guidance for future design. The equations that govern the dynamics of the three-dimensional motion of solid particles suspended in compressible gas flow through a rotating cascade of a turbine are discussed. The results obtained from the solution of these equations are presented to indicate the location on the turbine blade subjected to erosion damage. Some erosion data relevant to gas turbine engines are discussed. The concluding remarks include a global view of the state of the art of particulate flow problems in turbomachinery.
Coherent Structures in the Similarity Region of Two-Dimensional Turbulent Jets
Authors: Oler J. W. , Goldschmidt V. W.
Published: October 2009

The strongest indication of an ordered structure in the similarity region of plane jet flows is the well documented (but controversial) apparent “flapping” behavior. Previously, the negative correlation between probes placed on opposite sides of the jet centerline has been attributed to the periodic displacement of the mean velocity profile centerline about its average position, i.e., a flapping motion. The present investigation is directed at evaluating the premise of an essentially two-dimensional von Karman vortex street as being responsible for the apparent “flapping” behavior.
Laminar-To-Turbulent Transition on a Body of Revolution With an Extended Favorable Pressure Gradient Forebody
Authors: Hansen R. J. , Hoyt J. G.
Published: October 2009

An experimental study of the laminar-to-turbulent transition and resulting hydrodynamic forces on a body of revolution with a long, favorable pressure gradient forebody (i.e., where pressure is dropping and the flow accelerating) is reported. Over a substantial range of body velocity and angle of attack the favorable pressure gradient is shown to postpone transition to the point of laminar separation, and this extended laminar region results in a much lower hydrodynamic drag than is characteristic of an all-turbulent body. The intermittency of the boundary layer and the propagation characteristics of turbulent spots in the extended favorable pressure gradient region are quantified by hot film probes mounted flush with the body surface. The sensitivity of the boundary layer transition to three-dimensional surface roughness elements located in tandem (along a streamline) is also quantified. A number of such elements in tandem causes transition at a lower Reynolds number than would a single element of the same size, this effect becoming more pronounced with increasing number of roughness elements and decreasing space between them.
Nonlinear Impulsive Force on an Accelerating Container
Authors: Chwang Allen T. , Wang K. H.
Published: October 2009

The nonlinear theory developed by Chwang [1] is applied to calculate the hydrodynamic pressure force on an accelerating rectangular or circular container. The fluid inside the container is initially at rest and the motion of the container is impulsive. During the initial stage of this impulsive motion, no travelling free-surface waves are present, and the fluid simply piles up on one side of the container and subsides on the opposite side. When the horizontal displacement of the container is small in comparison with the horizontal dimension of the container as well as the undisturbed fluid depth, the small-time expansion method is applied to obtain the velocity potential of the fluid which is accurate up to and including the third-order solution. The second-order free surface elevation is found to be singular along the contact line between the fluid and the container wall.
PSL—An Economical Approach to the Numerical Analysis of Near-Wall, Elliptic Flow
Authors: Iacovides H. , Launder B. E.
Published: October 2009

The paper points out that, in the numerical computation of elliptic or three-dimensional turbulent flows, the neglect of pressure-variations across the very thin viscosity affected region near the wall allows a fine-grid analysis of this sublayer without prohibitive penalties in core or computational time. The scheme has been successfully applied to the three-dimensional flow around a U-bend.
Confined Flow in a Partially-Filled Rotating Horizontal Cylinder
Authors: Haji-Sheikh A. , Lakshimanarayanan R. , Lou David Y. S. , Ryan Phil J.
Published: October 2009

Experimental and analytical studies are reported for a Newtonian fluid in a partially-filled cylinder rotating about its centerline axis at constant angular speeds. Two fluids, glycerin and water, are used in this study. The analytical results are in good agreement with the experimental data. This comparison is based on the profiles of the free surfaces and the streamlines experimentally obtained using a flow visualization technique and as predicted by the analytical model. When the rotational speed is not high enough to cause solid body rotation of the fluid, due to excessive centrifugal force, a recirculation region forms at the lower portion of the cylinder. The profile of the free surface in this region depends on the relative magnitude of the body force and the viscous force. In general, two distinct flow regions can be recognized for a cylinder of infinite extent; a recirculating flow and a boundary-layer-type flow along the cylindrical wall. In addition to the volume of the fluid in the cylinder, there are two other parameters governing this problem; the Reynolds number and the ratio, G, of the Reynolds number to the Froude number.
Noise Generation in Cavitating Flows, the Submerged Jet
Authors: Franklin R. E. , McMillan J.
Published: October 2009

Measurements are reported of the pressure fluctuations in the near field of a submerged jet. The mechanisms by which the pressure fluctuations may be generated are discussed and estimates are presented of two of these, namely the transient oscillations of micro-bubbles of air excited by the pressure drop in the nozzle, and the cavitation of micro-bubbles by the turbulent pressure fluctuations in the jet mixing region.
Application of Signal Analysis to Cavitation
Authors: Martin C. Samuel , Rao P. Veerabhadra
Published: October 2009

The diagnostic facilities of the cross power spectrum and the coherence function have been employed to enhance the identification of not only the inception of cavitation, but also its level. Two piezoelectric pressure transducers placed in the downstream chamber of a model spool valve undergoing various levels of cavitation allowed for the use of both functions—the phase angle of the complex cross spectrum and the dimensionless coherence function—to sense clearly the difference between noise levels associated with a noncavitating jet from those once cavitation inception is attained. The cavitation noise within the chamber exhibited quite a regular character in terms of the phase difference between instruments for limited cavitation. Varying cavitation levels clearly illustrated the effect of bubble size on the attendant frequency range for which there was an extremely high coherence or nearly perfect causality.
On End Wall Effects in a Lid-Driven Cavity Flow
Authors: Koseff J. R. , Street R. L.
Published: October 2009

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.
The Lid-Driven Cavity Flow: A Synthesis of Qualitative and Quantitative Observations
Authors: Koseff J. R. , Street R. L.
Published: October 2009

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-Go¨rtler-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.
Numerical Study of Turbulent Axisymmetric Jets Impinging on a Flat Plate and Flowing Into an Axisymmetric Cavity
Authors: Amano R. S. , Brandt H.
Published: October 2009

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.
Pulsatile Flow Through a Branching Tube With Collapsing Walls: Volumetric Flow Redistribution
Authors: Davis R. B. , Schneck D. J. , Gutstein W. H.
Published: October 2009

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.
Critical Conditions and the Choking Mass Flow Rate in Nonequilibrium Wet Steam Flows
Authors: Young J. B.
Published: October 2009

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.
The Utilization of Specially Tailored Air Bubbles as Static Pressure Sensors in a Jet
Authors: Ooi K. K. , Acosta A. J.
Published: October 2009

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.
Mean Flow and Turbulence Measurements of Annular Swirling Flows
Authors: Yowakim F. M. , Kind R. J.
Published: October 2009

This paper presents the results of a detailed experimental investigation of swirling flows in a cylindrical annulus. Flows having nominal swirl angles of 0, 15, 30, and 45 degrees were measured. Mean velocity components, total and static pressures, wall shear and Reynolds stresses were measured. Mixing length and eddy viscosity distributions were deduced from the data. The majority of the flow field measurements were made with single-sensor hot-wire anemometer probes; six independent readings, each with a different sensor orientation, were made at each point. Consistency checks were applied wherever possible and indicate that the data are of high quality.
Turbulence Measurements With Symmetrically Bent V-Shaped Hot-Wires. Part 1: Principles of Operation
Authors: Hishida M. , Nagano Y.
Published: October 2009

A new anemometry technique has been developed for turbulence measurements near the wall, where the conventional X-wire method is subject to large errors due to aerodynamic disturbances caused by the tips of wire supports. The technique proposed in this study is founded on the principle of convective heat transfer from a symmetrically bent V-shaped hot-wire, which can be supported just like a cantilever. The present paper describes the details of effective cooling velocities of a V-shaped hot-wire, together with the related comments on its aeroelastic deformation and vibration.
An Optical Method for Determining Bubble Size Distributions—Part II: Application to Bubble Size Measurement in a Three-Phase Fluidized Bed
Authors: Meernik P. R. , Yuen M. C.
Published: October 2009

The light beam technique, described in Part I of a paper with the same title, was applied to a three-phase system (nitrogen, organic solvents, and glass particles) to study the equilibrium bubble size distributions. A range of liquid and gas flow rates, with respective superficial velocities of 1–8 cm/sec and 0.1–1.1 cm/s; and various particles, 2 mm diameter by 5 mm long cylinders and 1 to 5 mm diameter spheres, were considered. Typical average bubble diameters were measured to be in the range of 1.2 to 2 mm. For the range of flow conditions considered, the Sauter mean diameters, normalized by particle size, were found to be proportional to the Eotvos number and essentially independent of the liquid and gas fluxes.
Radial and Axial Turbulent Flow Measurements With an LDV in an Axisymmetric Sudden Expansion Air Flow
Authors: Durrett R. P. , Stevenson W. H. , Thompson H. D.
Published: October 2009

Radial velocity component measurements in cylindrical tubes have been difficult to make because of optical aberrations introduced by the curved tube wall. This is particularly troublesome in gas flows where refractive index matching techniques cannot be employed. The present investigation utilized a specially designed correction lens system to overcome this problem. As a result it was possible to map the axial and radial velocity behavior in detail for the air flow downstream of a sudden expansion in a cylindrical duct. Quantities measured and derived included mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds stress. The weak secondary recirculation zone existing just below the sudden expansion was clearly identified and mapped. Where possible the measurements were compared with numerical predictions based on a k-ε model.
The Mean Flow Structure Around and Within a Turbulent Junction or Horseshoe Vortex—Part I: The Upstream and Surrounding Three-Dimensional Boundary Layer
Authors: Menna J. D. , Pierce F. J.
Published: October 2009

The mean flow structure upstream, around, and in a turbulent junction or horseshoe vortex is reported for an incompressible, subsonic flow. This fully documented, unified, comprehensive, and self-consistent data base is offered as a benchmark or standard case for assessing the predictive capabilities of computational codes developed to predict this kind of complex flow. Part I of these papers defines the total flow being documented. The upstream and surrounding three-dimensional turbulent boundary layer-like flow away from separation has been documented with mean velocity field and turbulent kinetic energy field measurements made with hot film anemometry, and local wall shear stress measurements. Data are provided for an initial condition plane well upstream of the junction vortex flow to initiate a boundary layer calculation, and freestream or edge velocity, as well as floor static pressure, are reported to proceed with the solution. Part II of these papers covers the flow through separation and within the junction vortex flow.
The Mean Flow Structure Around and Within a Turbulent Junction or Horseshoe Vortex—Part II. The Separated and Junction Vortex Flow
Authors: Pierce F. J. , Harsh M. D.
Published: October 2009

The mean flow structure upstream, around, and in a turbulent junction or horseshoe vortex are reported for an incompressible, subsonic flow. This fully documented, unified, comprehensive, and self-consistent data base is offered as a benchmark or standard test case for assessing the predictive capabilities of computational codes developed to predict this kind of complex flow. The three-dimensional turbulent boundary layer-like flow upstream and around the separated junction vortex flow is described in a companion paper, Part I. Part II of these papers covers the flow through the separation region and in the vortex system. This portion of the flow has been documented with mean velocity, static pressure, and total pressure measurements using a very carefully calibrated five-hole probe. The streamwise vorticity field is calculated from the measured velocity field. Extensive floor static pressure measurements emphasizing the region of the vortex system, and static pressure measurements on the cylinder surface are also reported. Flow visualizations on the floor and cylinder surface show unusual detail and agree well both qualitatively and quantitatively with the various flow field measurements.
Determination of Incompressible Flow Friction in Smooth Circular and Noncircular Passages: A Generalized Approach Including Validation of the Nearly Century Old Hydraulic Diameter Concept
Authors: Obot N. T.
Published: October 2009

It has been demonstrated conclusively that the widely observed differences in data for frictional pressure coefficient between circular and noncircular passages derive from the inseparably connected effects of transition and the choice of a length scale. A relatively simple approach, the critical friction method (CFM), has been developed and when applied to triangular, rectangular, and concentric annular passages, the reduced data lie with remarkable consistency on the circular tube relations. In accordance with the theory of dynamical similarity, it has also been shown that noncircular duct data can be reduced using the hydraulic diameter or any arbitrarily defined length scale. The proposed method is what is needed to reconcile such data with those for circular tubes. With the hydraulic diameter, the critical friction factor almost converges to a universal value for all passages and the correction is simply that required to account for the difference in critical Reynolds number. By contrast, with any other linear parameter, two corrections are needed to compensate for variations in critical friction factor and Reynolds number. Application of the method to roughened passages is discussed.
A model for quantitative correction of coronary calcium scores on multidetector, dual source, and electron beam computed tomography for influences of linear motion, calcification density, and temporal resolution: A cardiac phantom study
Authors: Greuter M. J. W. , Groen J. M. , Nicolai L. J. , Dijkstra H. , Oudkerk M.
Published: October 2009

Purpose:

The objective of this study is to quantify the influence of linear motion, calcification density, and temporal resolution on coronary calcium determination using multidetector computed tomography (MDCT), dual source CT (DSCT), and electron beam tomography (EBT) and to find a quantitative method which corrects for the influences of these parameters using a linear moving cardiac phantom.

Methods:

On a robotic arm with artificial arteries with four calcifications of increasing density, a linear movement was applied between 0 and 120 mm/s (step of 10 mm/s). The phantom was scanned five times on 64‐slice MDCT, DSCT, and EBT using a standard acquisition protocol. The average Agatston, volume, and mass scores were determined for each velocity, calcification, and scanner. Susceptibility to motion was quantified using a cardiac motion susceptibility (CMS) index. Resemblance to EBT and physical volume and mass was quantified using a index.

Results:

Increasing motion artifacts were observed at increasing velocities on all scanners, with increasing severity from EBT to DSCT to 64‐slice MDCT. The calcium score showed a linear dependency on motion from which a correction factor could be derived. This correction factor showed a linear dependency on the mean calcification density with a good fit for all three scoring methods and all three scanners . The slope and offset of this correction factor showed a linear dependency on temporal resolution with a good fit for all three scoring methods and all three scanners . CMS was minimal for EBT and increasing values were observed for DSCT and highest values for 64‐slice MDCT. CMS was minimal for mass score and increasing values were observed for volume score and highest values for Agatston score. For all densities and scoring methods DSCT showed on average the closest resemblance to EBT calcium scores. When using the correction factor, CMS index decreased on average by 15% and index decreased by 35%.

Conclusions:

Calcium scores determined on DSCT and 64‐slice MDCT are highly susceptible to motion as compared to EBT. The mass score is less susceptible to motion compared to volume and Agatston score. Calcium scores determined on DSCT bear a closer resemblance to EBT obtained calcium scores than 64‐slice MDCT. In addition, the calcium score is highly dependent on the average density of individual calcifications and the dependency of the calcium score on motion showed a linear behavior on calcification density. From these relations, a quantitative method could be derived which corrects the measured calcium score for the influence of linear motion, mean calcification density, and temporal resolution.
Magnetic resonance microwave absorption imaging: Feasibility of signal detection
Authors: Xie Bin , Weaver John B. , Meaney Paul M. , Paulsen Keith D.
Published: October 2009

Purpose:

Magnetic resonance (MR) technique was used to detect small displacements induced by localized absorption of pulsed 434 MHz microwave power as a potential method for tumor detection.

Methods:

Phase contrast subtraction was used to separate the phase change due to motion from thermoelastic expansion from other contributions to phase variation such as the bulk temperature rise of the medium and phase offsets from the MR scanner itself. A simple set of experiments was performed where the motion was constrained to be one dimensional which provided controls on the data acquisition and motion extraction procedures. Specifically, the MR‐detected motion signal was isolated by altering the direction of the microwave‐induced motion and sampling the response with motion encoding gradients in all three directions when the microwave power was turned on and turned off.

Results:

Successful signal detection, as evidenced by the recording of a systematic alternating (zigzag) phase pattern, occurred only when the motion encoding was in parallel with either the vertical or horizontal direction of the microwave‐induced motion on both 10 and 4 mm spatial scales.

Conclusions:

These results demonstrate, for the first time, that motion associated with thermoelastic expansion from the absorption of pulsed microwave power can be detected with MR.
Accuracy of real time noninvasive temperature measurements using magnetic resonance thermal imaging in patients treated for high grade extremity soft tissue sarcomas
Authors: Craciunescu Oana I. , Stauffer Paul R. , Soher Brian J. , Wyatt Cory R. , Arabe Omar , Maccarini Paolo , Das Shiva K. , Cheng Kung‐Shan , Wong Terence Z. , Jones Ellen L. , Dewhirst Mark W. , Vujaskovic Zeljko , MacFall James R.
Published: October 2009

Purpose:

To establish accuracy of real time noninvasive temperature measurements using magnetic resonance thermal imaging in patients treated for high grade extremity soft tissue sarcomas.

Methods:

Protocol patients with advanced extremity sarcomas were treated with external beam radiation therapy and hyperthermia. Invasive temperature measures were compared to noninvasive magnetic resonance thermal imaging (MRTI) at 1.5 T performed during hyperthermia. Volumetric temperature rise images were obtained using the proton resonance frequency shift (PRFS) technique during heating in a 140 MHz miniannular phased array applicator. MRTI temperature changes were compared to invasive measurements of temperature with a multisensor fiber optic probe inside a #15 g catheter in the tumor. Since the PRFS technique is sensitive to drifts in the primary imaging magnetic field, temperature change distributions were corrected automatically during treatment using temperature‐stable reference materials to characterize field changes in 3D. The authors analyzed MRT images and compared, in evaluable treatments, MR‐derived temperatures to invasive temperatures measured in extremity sarcomas. Small regions of interest (ROIs) were specified near each invasive sensor identified on MR images. Temperature changes in the interstitial sensors were compared to the corresponding ROI PRFS‐based temperature changes over the entire treatment and over the steady‐state period. Nonevaluable treatments (motion/imaging artifacts, noncorrectable drifts) were not included in the analysis.

Results:

The mean difference between MRTI and interstitial probe measurements was for the entire heating time and for the time at steady state. These values were obtained from both tumor and normal tissue ROIs. When the analysis is done on just the tumor ROIs, the mean difference for the whole power on time was and during the period of steady state was .

Conclusions:

The data show that for evaluable treatments, excellent correlation of MRTI‐ROI and invasive measurements can be achieved, but that motion and other artifacts are still serious challenges that must be overcome in future work.