bluuebunny/crossref_metadata_2025 huggingface dataset:
A Note on the Effect of Short and Long Laminar Separation Bubbles on Desinent Cavitation
Authors: Arakeri V. H. , Carroll J. A. , Holl J. W.
Published: October 2009

Earlier desinent cavitation studies on a 1/8 caliber ogive by one of the authors (J. W. H.) showed a sudden change in the magnitude of the desinent cavitation number at a critical velocity. In the present work it is shown by means of oil-film flow visualization that below the critical velocity a long laminar separation bubble exists whereas above the critical velocity the laminar separation bubble is short. Thus the desinent cavitation characteristics of a 1/8 caliber ogive are governed by the nature of the viscous flow around the body.
The Third Two-Dimensional Problem of Three-Dimensional Blade Systems of Hydraulic Machines—Part 2: Analytical Results
Authors: Agarwal P. K. , Viktorov G. V.
Published: October 2009

This is the second part of a study of the “third” two-dimensional problem of three-dimensional blade systems of hydraulic machines. Part I described the formulation of the problem and the proposed method of solution to determine the velocity field on surfaces orthogonal to mean axisymmetric stream surfaces. Part II presents the numerical method of solving the integral equations; a few numerical examples for actual impellers/runners are also given. The results are presented in a series of figures and tables showing the distribution of the velocity component c2 along the blade profile on the surface q1 = const. The purpose of these numerical examples is to demonstrate the method and to help create a general understanding and awareness of the flow conditions existing in the runner passage.
A Comparison of Two Optical Techniques for Measuring Cavitation Nuclei
Authors: Billet M. L. , Gates E. M.
Published: October 2009

Several devices have been developed or adapted to the use of measuring “nucleating sources” in a liquid including acoustic methods, direct observation (e.g. microscopy and holography), single particle counters, light scattering and light extinction. With experience two techniques have become more favored than the others, namely: holography and light scattering. However, with the exception of Peterson et al’s study no attempt has been made to simultaneously compare these two techniques under actual test conditions so that some confidence may be gained in deducing the number and type of nuclei from the record produced by either method. The purpose of the present paper is then to report and compare some nuclei populations which were recorded simultaneously by both methods during a series of cavitation inception tests. Measurements of nuclei populations were made in two facilities located at the California Institute of Technology, the Low Turbulence Water Tunnel (LTWT) and the High Speed Water Tunnel (HSWT) which are known to have substantially different nuclei distributions. In each facility nuclei populations were recorded at various combinations of tunnel velocity, pressure and pressure-time histories in an effort to produce different distributions and also to enable one to deduce from the laser scattering results the composition of the nuclei, i.e., solid particulates or bubbles. This deduction could then be checked with the holographic results. Simultaneous nuclei population measurements were recorded in the LTWT, whereas measurements of nuclei in the HSWT were obtained at separate times approximately eleven months apart. Since both methods have different characteristic size detection ranges, they could be compared directly only in the overlapping size range, namely: 10-50 microns diameter. In the LTWT where the populations were recorded simultaneously, there was some good agreement between not only the numbers but also the type of nuclei (mainly gas bubbles). However, the scattering technique indicated somewhat fewer nuclei in most cases. In addition, the scattering technique indicated fewer nuclei in the HSWT than had been previously measured by holography. Although there was some discrepancy between numbers of nuclei, both techniques demonstrated (directly from holography and by inference from the scattering results) that the nuclei were primarily solid particulates rather than gas bubbles.
Observations of the Various Types of Limited Cavitation on Axisymmetric Bodies
Authors: Holl J. W. , Carroll J. A.
Published: October 2009

Observations are presented of various types of limited cavitation on 5.1 cm diameter Schiebe, hemispherical, and DTNSRDC noses. These three noses were selected to give various flow states over the range of test speeds 6.1–21.3 m/s ranging from laminar separation for all speeds (hemispherical nose) to nonseparated flow for all speeds (Schiebe nose) with the DTNSRDC nose experiencing both separated and nonseparated flow over the speed range. The types of cavitation observed fall into two broad classes, namely transient and attached. Transient cavitation was observed in three forms, namely travelling-bubble, travelling-patch and bubble-ring. Three types of attached cavitation were observed, namely band, fixed-patch and developed. Bubble-ring and band cavitation are observed only on a body with laminar separation as noted previously by Arakeri and Acosta. Bubble-ring cavitation has been observed only on hemispherical and eighth caliber ogive noses. The desinent cavitation numbers for band and bubble-ring cavitation on the hemispherical nose are related to measured mean and fluctuating pressure data. Travelling cavitation was the most prevalent type of cavitation and the cavitation number decreased with speed and increased with air content. An analysis of travelling cavitation data from several investigations is presented. The cavitation number for fixed-patch cavitation increases with speed which suggests that surface roughness effects are involved.
On the Equilibrium of Cavitation Nuclei in Liquid-Gas Solutions
Authors: Cha Y. S.
Published: October 2009

The stability of a spherical bubble in a two-component two-phase system is examined by employing the thermodynamic theory of dilute solutions. It is shown that a bubble can remain in a state of stable equilibrium provided that the ratio of the total number of moles of the solute to the total number of moles of the solvent in the system is not extremely small and that the system pressure falls between an upper bound (dissolution limit) and a lower bound (cavitation limit). The results of the analysis provide a theoretical basis for the persistence of microbubbles in a saturated liquid-gas solution. Thus to a certain extent, the results also help to resolve the dilemma that exists in the field of cavitation due to (1) the necessity of postulating the existence of microbubbles; and (2) the lack of theoretical justification for the persistence of such bubbles in a liquid.
Fluid Flow Through a Class of Highly-Deformable Porous Media. Part I: Experiments With Air
Authors: Beavers G. S. , Hajji A. , Sparrow E. M.
Published: October 2009

This paper, together with a companion paper which follows, describes a many-faceted experimental investigation aimed at determining basic characteristics of fluid flow through deformable porous media. A major focus of the work is to establish the validity and the range of applicability of a simple analytical model for the fluid flow. The present paper describes experiments with a gas (air) as the working fluid, while the companion paper (Part II) deals with liquid-flow (i.e., water-flow) experiments. The experiments encompassed three distinct phases. In the first phase, the stress-deformation characteristics were measured (without fluid flow). In the second, flow-related material properties that are relevant to the analytical model (e.g., permeability, Forchheimer coefficient) were determined. The third phase consisted of measurements of mass flow rate as a function of applied pressure differential. The results of the first two phases were used as input to the analytical model, which yielded predictions of mass flow versus applied pressure. These predictions were shown to be in very good agreement with the experimental results, for those conditions where the model is applicable. Two unusual features of the participating deformable materials (polyurethane foams) were encountered, namely, a decrease of cross-sectional area with increasing compression and a slow relaxation of the internal stresses at a fixed compression.
Fluid Flow Through a Class of Highly-Deformable Porous Media. Part II: Experiments With Water
Authors: Beavers G. S. , Wittenberg K. , Sparrow E. M.
Published: October 2009

Experiments were performed to explore the relationships between liquid-saturated and gas-saturated deformable porous media. Water and air served as the participating fluids. From quasi-static compression experiments (no fluid flow), it was found that the force required to compress a given deformable porous material is substantially less when the material is water-saturated than when it is in air. Water flow measurements yielded flow rate-pressure drop results which are compared with analytical predictions. The predictions were based on input values of certain material flow parameters which had been determined in previous air flow experiments. The observed level of agreement between the predictions and the water flow measurements lends support to the notion that the flow parameters are independent of the participating fluid. In the course of establishing the effects of the participating fluid, the stress relaxation and aging phenomena were quantified. The former is a relaxation of the internal stress in a deformable material which occurs after a compression is imposed and maintained. The latter is a process whereby the deformation characteristics change when the material is subjected to a succession of compressions.
A Modified Form of the k-ε Model for Predicting Wall Turbulence
Authors: Lam C. K. G. , Bremhorst K.
Published: October 2009

The high Reynolds number form of the k-ε model is extended and tested by application to fully developed pipe flow. It is established that the model is valid throughout the fully turbulent, semilaminar and laminar regions of the flow. Unlike many previously proposed forms of the k-ε model, the present form does not have to be used in conjunction with empirical wall function formulas and does not include additional terms in the k and ε equations. Comparison between predicted and measured dissipation rate in the important wall region is also possible.
Effect of Wind-Tunnel Walls on the Drag of a Sphere
Authors: Awbi H. B. , Tan S. H.
Published: October 2009

The wind-tunnel wall interference effect on the drag and base pressure coefficients is investigated experimentally in the range of Reynolds-number independence. The drag results of Achenbach for large blockage ratios are also included, thus covering a range of blockage ratio between 6.3 to 83.9 percent. The measured drag is corrected using blockage correction formulas for three-dimensional flow obtained by the method of images and the analytical equation of Maskell. The results given by Maskell’s method are found to be under-corrected by up to 20 percent and the method of images is totally inadequate. Replacing the blockage factor, ε, in Maskell’s equation by an empirically determined value improved the corrections considerably.
Laminar Flow in a Cylindrical Container With a Rotating Cover
Authors: Bertela` Manlio , Gori Fabio
Published: October 2009

Unsteady and steady flow in a cylindrical chamber with a rotating cover has been studied for two Reynolds numbers and three aspect ratio values. The structure of the velocity and pressure fields in the apparatus is described. Primary and secondary volumetric flow rates and torque coefficients are also calculated for all six cases solved.
Discharge Jet Interaction With Multiple Port Diffusers
Authors: Sorrell F. Y. , Smith B. W.
Published: October 2009

A model for the flow dynamics and mixing in the near-field of a multiple port outfall diffuser is postulated. It employs the equations for gross conservation of mass, momentum, and buoyancy of the fluid in the discharge jet or plume. These equations are obtained by assuming flow similarity and then integrating over the cross-sectional area of the plume. Two distinct interactions of the discharge jets or plumes are included in the model. These are the interaction of the individual round jets from the diffuser ports and the merging of the plume from either side of the diffuser, over the top of the diffuser. The resulting equations are closed by the “entrainment assumption” and solved numerically. Results provide the velocity, width, and dilution of the jet or plume. Calculations were made for a number of cases where experimental results were available. The model gives reasonable agreement with the experiments over a wide range of discharge conditions and over the complete range of flow patterns. In most cases it slightly underestimates the mixing or dilution. Therefore the model should be useful in determining the minimum dilution that can be expected from any marine outfall.
Transient Characteristics of a Centrifugal Pump During Starting Period
Authors: Tsukamoto H. , Ohashi H.
Published: October 2009

A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed. Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes. Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results. As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period.
The Effects of Roughness and Shear on Vortex Shedding Cell Lengths Behind a Circular Cylinder
Authors: Rooney D. M. , Peltzer R. D.
Published: October 2009

Circular cylinders of aspect ratio L/D=17 were tested in a wind tunnel under a wide range of spanwise upstream velocity shears. The correlation between upstream shear, characterized by a nondimensional shear parameter β, and the spanwise lengths of constant vortex shedding frequency was sought for both smooth and rough cylinders in transitional Reynolds numbers flows. Among the significant conclusions are that the spanwise range in shedding frequencies decreases with increasing roughness, the average constant shedding frequency cell length increases with increasing roughness for constant shear, and the average cell length decreases with increasing upstream shear for constant roughness.
Effects Of Surface Solidification on the Stability Of Multi-Layered Liquid Films
Authors: Lin S. P.
Published: October 2009

The linear stability problem of a n-layered liquid film with a solidified liquid-air interface is reviewed. The general formulation is applied to the special case of a two-layered film flow down an inclined plane. A stability condition is given explicitly in terms of the density, viscosity and thickness ratios. Based on this condition it is found that solidification of the free surface may have the effects of stabilizing the interfacial shear waves and destabilizing the gravity-capillary waves associated with top-heavy density stratification.
Effects of Turbulence on the Pressure Distribution Around a Square
Cylinder and Possibility of Reduction
Authors: Kwok K. C. S.
Published: October 2009

When a prismatic structure is subjected to air flow, especially at small angle of wind incidence, the separated shear layers may reattach onto the streamwise surface. The turbulent mixing in the shear layers and the extrainment of fluid results in highly fluctuating and strongly negative pressures under the reattaching shear layers. Wind tunnel tests were carried out to determine the pressure distribution around a square cylinder. It was found that an increase in turbulence, in particular fine scale turbulence, significantly altered the pressure distribution, the transverse force characteristic, and hence the galloping behavior of the square cylinder. When small vanes were fitted to the corners of the cylinder, and by maintaining a vent between the vane and the corner, the magnitude of the negative mean and peak pressure coefficients under the shear layer were substantially reduced.
Boundary-Layer Development on a Circular Cylinder With Ribs
Authors: Gu¨ven O. , Farell C. , Patel V. C.
Published: October 2009

An integral method for the calculation of the boundary layer development on a circular cylinder with external meridional ribs is presented. The calculation method, which takes into account the effect of the ribs on the laminar and turbulent boundary layers and on transition, gives results which are in qualitative agreement with experimental data. Analytical results obtained with this method shed some light on the influence of rib roughness on boundary-layer development and support earlier arguments and conclusions derived from experimental data on the effect of external ribs or stakes on the mean flow around rounded structures at large Reynolds numbers.
LDV Measurements Near a Vortex Shedding Strut Mounted in a Pipe
Authors: Yeh T. T. , Robertson Baldwin , Mattar W. M.
Published: October 2009

The velocity field around vortex shedding strut mounted in a circular pipe has been in detail with a laser Doppler velocimeter (LDV) at a pipe Reynolds number equal to 90,000. The instantaneous velocity is decomposed into mean, periodic, and random components. Only the first two harmonics are large enough to be detected; the large-scale structure can be characterized by just these two these and the mean. Profiles of the different velocity terms are given upstream of, downstream of, and close to the strut. The two-dimensional velocity vector field of the mean flow on the transverse diametral plane of symmetry is presented along with its streamlines. Finally, for each spatial component, profiles of vortex visibility, the ratio of the energy of a periodic component to the total fluctuating energy in a narrow frequency band, are given.
Aerodynamic Studies on Swirled Coaxial Jets From Nozzles With Divergent Quarls
Authors: Dixon T. F. , Truelove J. S. , Wall T. F.
Published: October 2009

The aerodynamic characteristics of strongly swirled coaxial jets issuing from a divergent nozzle into stagnant-air surroundings have been studied. Maps of the central reverse-flow zone and detailed measurements of mean velocity have been obtained in the region close to the exit of the nozzles and the effects of varying the level of swirl and the ratio of the momenta in the central and annular jets have been examined. The level of swirl and the momentum flux ratio are found to influence significantly the flow type and stability. The measurements are compared with calculations obtained by numerical solution of the time-averaged equations governing conservation of mass and momentum. The calculation procedure is also used to examine the effects of burner geometry and heat release on flow type.
Flow in a Rectangular Diffuser With Local Flow Detachment in the Corner Region
Authors: Gessner F. B. , Chan Y. L.
Published: October 2009

An experimental study was conducted in order to examine the nature of flow within a high-inlet-aspect-ratio rectangular diffuser with locally detached flow in the corner region, but attached flow elsewhere in the diffuser. The results include flow visualization data corresponding to tuft and oil flow patterns observed on the diffuser walls and flow angle data taken in the immediate vicinity of the corner. Axial mean velocity distributions and local wall shear stress profiles are also presented. Analysis of the results provides new insight into the structure of separated, three-dimensional corner flows, wherein combined attached and detached flow conditions exist simultaneously at each streamwise location.
Generation and Size Distribution of Droplet in Annular Two-Phase Flow
Authors: Kataoka Isao , Ishii Mamoru , Mishima Kaichiro
Published: October 2009

The mean droplet size and size distribution are important for detailed mechanistic modeling of annular two-phase flow. A large number of experimental data indicate that the standard Weber number criterion based on the relative velocity between droplets and gas flow predicts far too large droplet sizes. Therefore, it was postulated that the majority of the droplets were generated at the time of entrainment and the size distribution was the direct reflection of the droplet entrainment mechanism based on roll-wave shearing off. A detailed model of the droplet size in annular flow was then developed based on the above assumption. The correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data. A comparison with experimental data indicated that indeed the postulated mechanism has been the dominant factor in determining the drop size. Furthermore, a large number of data can be successfully correlated by the present model. These correlations can supply accurate information on droplet size in annular flow which has not been available previously.
Analysis of Turbulent Gas-Solid Suspension Flow in a Pipe
Authors: Choi Young Don , Chung Myung Kyoon
Published: October 2009

The mixing length theory is extended to close the relevant momentum equations for two-phase turbulent flow at a first-order closure level. It is assumed that the mass fraction of the particles is on the order of unity, that the particle size is so small that the particles are fully suspended in the primary fluid, and that the relaxation time scale of the particles is sufficiently small compared with the time scale of the energy containing eddies so that the suspended particles are fully responsive to the fluctuating turbulent field. Bulk motion of the particles is treated as a secondary fluid flow with its own virtual viscosity. The proposed closure is applied to a fully developed gas-solid pipe flow in which the particles are assumed to be uniformly distributed across the pipe section. Predicted velocity profiles and the friction factors are in good agreement with available experimental data.
The Collapse of a Gas Bubble Attached to a Solid Wall by a Shock Wave and the Induced Impact Pressure
Authors: Tomita Y. , Shima A. , Takahashi K.
Published: October 2009

An experimental study was made on the collapse of a gas bubble attached to a solid wall by a shock wave. The collapse process of the bubble and the induced impact wall pressure were measured simultaneously by means of a high speed camera and a pressure transducer, respectively. Consequently, it was found that the impact wall pressure was very sensitive to the factors such as the bubble size, the strength of shock wave and the distance from the origin of shock wave to the gas bubble, and in some cases it became larger than that generated by a shock wave directly impinging on the solid wall without a gas bubble.
Pressure Field Generated by Nonspherical Bubble Collapse
Authors: Chahine G. L. , Bovis A. G.
Published: October 2009

The method of matched asymptotic expansions is used to investigate the behavior of a collapsing bubble near a solid wall. Cases are studied in which the ratio ε between the initial spherical bubble radius and its distance from the wall is small. Expansions in powers of ε lead to a simple system of differential equations which is solved numerically. The bubble shape, the velocity potential and the pressure field are determined as functions of time. The deformation of the bubble is a singular perturbation of the pressure field around it. An increase in the value of ε augments the pressure on the solid wall by orders of magnitude. The influence of surface tension and the proximity of the wall, gas content and its law of compression, are investigated. The results are compared to previous investigations. One advantage of the method employed is the fact that it leads to a numerical solution which costs very little computer time. In addition, it can be extended very easily to more complex cases such as multibubble configurations or to walls coated with elastomeric coatings.
Effects of Entrained Air on the Performance of a Horizontal Axial-Flow Pump
Authors: Murakami Mitsukiyo , Minemura Kiyoshi
Published: October 2009

The performance of an axial-flow pump was investigated under air-admitting conditions and the results were compared with those obtained for radial-flow pumps investigated in our previous studies. For the axial-flow pump we measured head as a function of impeller speed, liquid flow rate, and air void fraction. Flow visualization was performed and we correlated air bubble size as a function of Weber number based on mean impeller velocity. Overall flow patterns and the locations of air coalesence within the impeller were observed and diagrammed. These data contribute to earlier data obtained by ourselves and others to develop analytical models to predict pump performance degradation due to air admittance.
Fluid Transient Analysis in Pipelines With Nonuniform Liquid Density
Authors: Webb S. W. , Caves J. L.
Published: October 2009

A fluid transient in a system with steady nonuniform liquid density can be analyzed by a single density computer program by modification of the input parameters. These changes allow the program to solve the correct characteristic equations with appropriate initial and boundary conditions. The applicability of the approach has been demonstrated by a transient analysis of a reservoir, pipeline, valve problem and comparing the results.
Review: Turbulent Developing Pipe Flow
Authors: Klein A.
Published: October 2009

Experimental results on turbulent developing pipe flow are reviewed. Upstream conditions are shown to have a large effect, in particular on the development of the velocity profile. It is demonstrated also that the blockage factor, when plotted against the Reynolds number defined with flow distance, is the parameter best suited to indicate the onset and termination of transition.
Review: Effects of Inlet Conditions on Conical-Diffuser Performance
Authors: Klein A.
Published: October 2009

The available experimental evidence of the effects of inlet conditions on the performance of conical diffusers with a free discharge is reviewed. The effects of inlet boundary layer thickness blockage, inlet shape parameter, turbulence, and Reynolds number are discussed. It is shown that many of the inconsistencies between different sources of data are the result of nonturbulent approach flows. Graphs are presented as guidelines for diffuser design.
Historical Review of Real-Fluid Isentropic Flow Models
Authors: Sullivan D. A.
Published: October 2009

The analysis of steady, one-dimensional, isentropic flow of nonideal compressible fluids is simplified greatly by the use of an approximate model for the PV or Pρ relation, this relation being called the isentrope equation. The simplest isentrope model is the perfect-gas or polytrope equation PVn = constant. During the past 80 years, five isentrope equations have evolved: the polytrope, Walker, van der Waals, Rayleigh, and Callendar models. The historical development and limitations of each model are discussed. Only the polytrope and Rayleigh model yield simple, closed-form, analytic solutions for isentropic flow properties. A comparison with calculated data for sonic flow properties reveals the superiority of the Rayleigh model for the prediction of isentropic flow.
Inception of Cavitation From a Backward Facing Step
Authors: Arakeri V. H. , Ramarajan V.
Published: October 2009

Cavitation inception measurements are reported for flow past a downstream facing step with the height of the step varying from about 0.4 to 5 percent of the forebody diameter. The forebody was a 49 mm hemispherical nose and σi values were found to be very strong function of the height of the step. In addition, σi values were found to depend on whether the boundary layer approaching the step was laminar or turbulent. Generally σi values for turbulent case were lower.
Optimum Strut-Configuration for Downstream Annular Diffusers With Variable Swirling Inlet Flow
Authors: Senoo Y. , Kawaguchi N. , Kojima T. , Nishi M.
Published: October 2009

Using three conical wall annular diffusers, geometries of struts mounted at the inlet tube were studied which were suitable for both the swirling inlet flow and the nonswirling inlet flow. Struts with an airfoil section which were installed at a small stagger angle served as a decelerating cascade for the swirling inlet flow, and a pressure rise was achieved across the struts. Furthermore, the residual weak swirl behind the struts improved the performance of downstream diffusers. For nonswirling inlet flow the struts induced a weak swirl which improved the performance of the diffuser. That is, if struts are designed properly, the performance of annular diffusers is improved by struts for a wide variation of swirl angle of inlet flow.
Developing Region of Laminar Jets With Parabolic Exit Velocity Profiles
Authors: Rankin G. W. , Sridhar K.
Published: October 2009

An approximate solution to the velocity distribution in a submerged axisymmetric, laminar jet which issues from a long tube is presented. The solution is a modification of that of Okabe [17] and takes into account the changes that occur in the parabolic profile downstream of the jet exit. Comparisons are made with experimental data and other approximate theories taken from the literature.
A Comparison of Cold and Reacting Flows Around a Bluff-Body Flame Stabilizer
Authors: Fujii S. , Eguchi K.
Published: October 2009

A confined oblique flame anchored on a bluff object was considered in a homogeneous propane/air mixture. A laser velocimeter employing a unique single-particle processor was used to quantify the turbulence velocity as well as spectrum. The results with combustion presented a striking contrast to the corresponding cold flow data. A major conclusion of the work is that the apparent suppression of turbulence observed in the separated combustion flow may be attributed to the significant dilatation effect by heat release in sheared flow regions. No vortex shedding was detected, and the negative production zone of turbulence energy was not observed. The turbulence structure was significantly distorted at the visible flame location.
Turbulent Shear Flows Over a Step Change in Surface Roughness
Authors: Schofield W. H.
Published: October 2009

A large body of data now exists on the response of turbulent shear flows to sudden or step changes in surface roughness. Authors have used a variety of methods to reduce and present the data; thus a consistent description of these flows has not yet been presented. This paper presents all available data reduced in a uniform way. As there are extremely few Reynolds stress measurements within this large body of data, the analyses presented here are necessarily based on mean velocity profiles. It is shown that the growth rate of the new internal layer for all types of flow both with and without pressure gradient can be described in terms of a single length scale associated with the new wall condition. It is also shown that all mean velocity profiles after a step change in roughness display semi-logarithmic distributions. However, in the region immediately downstream of a step the constant of proportionality (the von Karman constant) has values different from the usual equilibrium value of 0.41. The differences appear to be large with values for the constant ranging between about 0.2 to 0.8.
Drag Reducing Polymer in Helicoidal Flow
Authors: Kuo J. T. , Kovasznay L. S. G.
Published: October 2009

A novel flow configuration was explored for the study of the behavior of drag reducing polymers. A screw pump consisting of a smooth cylinder and a concentrically placed screw was used to create a strongly three-dimensional but essentially laminar flow. In the first phase of the study, the static pressure head developed by the screw pump was measured as a function of polymer concentration (polyox 10 to 100 ppm in water). A large increase of the developed head was observed that behaved in an analogous manner to drag reduction as far as concentration and straining of the polymer solution was concerned. In the second phase of the study, a new apparatus was constructed and the additional parameter of a superimposed through flow was included and the degree of failure of the superposition principle was established. Sensitivity of the phenomenon to chemicals like HCl, HNO3, and NaOH in the polymer solution was also studied. When the effect of these chemicals on the polymer solution flow behavior was presented in terms of the pH value of the polymer solution, it showed a similar trend to those observed in drag reduction.
Search for Large-Scale Coherent Structures in the Nearly Self-Preserving Region of a Turbulent Axisymmetric Jet
Authors: Tso J. , Kovasznay L. S. G. , Hussain A. K. M. F.
Published: October 2009

In an attempt to explore the existence of large-scale coherent structures in the nearly self-preserving region of an axisymmetric free air jet, a 2.54 cm air jet at a Reynolds number ReD = 6.8 × 104 has been investigated for x/D≥40 via both long and short time-averaged space-time correlation measurements. Conventional space-time correlation data with probe separations in the stream wise direction by as much as 25 diameters suggest the passage of large-scale organized structures. The radial extent of these structures is about one local jet diameter, and the azimuthal extent is about a quadrant of the cross-section. Recurring quasi-periodic patterns are observed in the time series of short time-averaged correlations between longitudinal velocity fluctuations obtained with two arrays of hot-wires separated in the streamwise direction. These orderly patterns provide direct evidence for the existence of these structures. Quantitative details of these structures are now being investigated.
The Initiation Of Gaseous Microbubble Growth In Laminar Separation Bubbles
Authors: Parkin B. R.
Published: October 2009

Flow conditions surrounding bubble-ring cavitation inception on hemispherical headforms are analyzed with respect to the initiation of air diffusion into microbubbles as is observed to occur at fixed positions in the boundary layer. Fairly recent observations have shown this phenomenon to occur in the laminar separation bubble on the body. The analysis shows, in agreement with the body of experimental evidence now available, that gaseous growth must be preceded by a period of vaporous growth starting in regions of low pressure upstream of the laminar separation bubble. It also appears that the most favorable condition for the initiation of gaseous growth should occur when a typical vapor bubble reaches its maximum radius as it enters the laminar separation bubble. The conditions for the initiation of subsequent gaseous growth, once the cavitation bubble is stabilized in the laminar separation zone, are more demanding. Nevertheless, it is found that the liquid in the water surrounding the bubble in the separation zone is definitely supersaturated for most flows of experimental or practical interest. Therefore, gaseous growth, as well as vaporous growth, is definitely to be associated with the onset of bubble-ring cavitation on both theoretical and experimental grounds.
Liquid Sheet Jet Experiments: Comparison With Linear Theory
Authors: Asare H. R. , Takahashi R. K. , Hoffman M. A.
Published: October 2009

It has been proposed to protect the structural walls of a future laser fusion reactor with a curtain or fluid-wall of liquid lithium jets. As part of the investigation of this concept, experiments have been performed on planar sheet water jets issuing vertically downward from slit nozzles. The nozzles were subjected to transverse forced harmonic excitation to simulate the vibrational environment of the laser fusion reactor, and experiments were run at both 1 atm and at lower ambient pressures. Linear stability theory is shown to predict the onset of the unstable regime and the initial spatial growth rates quite well for cases where the amplitudes of the nozzle vibration are not too large and the waveform is nearly sinusoidal. In addition, both the linear theory and a simplified trajectory theory are shown to predict the initial wave envelope amplitudes very well. For larger amplitude nozzle excitation, the waveform becomes highly nonlinear and nonsinusoidal and can resemble a sawtooth waveform in some cases; these latter experimental results can only be partially explained by existing theories at the present time.
Generation of Oscillating Jets
Authors: Favre-Marinet M. , Binder G. , Hac Te. V.
Published: October 2009

It is shown that periodic angular oscillations can be forced on a jet issuing from a nozzle based on the Coanda effect by alternate blowing from the two sides. The influence of the various geometric and dynamic parameters such as the jet width, the blowing direction, the blowing generating pressure, the jet velocity, and frequency has been investigated. The angular deflection can conveniently be controlled by the blowing pressure.
A Self-Correcting and Self-Checking Gas Turbine Meter
Authors: Lee W. F. Z. , Blakeslee D. C. , White R. V.
Published: October 2009

A new metering concept of a self-correcting and self-checking turbine meter is described in which a sensor rotor downstream from the main rotor senses and responds to changes in the exit angle of the fluid leaving the main rotor. The output from the sensor rotor is then electronically combined with the output from the main rotor to produce an adjusted output which automatically and continuously corrects to original meter calibration accuracy. This takes place despite changes in retarding torques, bearing wear and/or upstream conditions occurring in field operations over those which were experienced during calibration. The ratio of the sensor rotor output to the main rotor output at operating conditions is also automatically and continuously compared with that at calibration conditions. This provides an indication of the amount of accuracy deviation from initial calibration that is being corrected by the sensor rotor. This concept is studied theoretically and experimentally. Both the theory and test results (laboratory and field) confirm the concept’s validity and practicability.
Direct Force Wall Shear Measurements in Pressure-Driven Three-Dimensional Turbulent Boundary Layers
Authors: McAllister J. E. , Pierce F. J. , Tennant M. H.
Published: October 2009

Unique, simultaneous direct measurements of the magnitude and direction of the local wall shear stress in a pressure-driven three-dimensional turbulent boundary layer are presented. The flow is also described with an oil streak wall flow pattern, a map of the wall shear stress-wall pressure gradient orientations, a comparison of the wall shear stress directions relative to the directions of the nearest wall velocity as measured with a typical, small boundary layer directionally sensitive claw probe, as well as limiting wall streamline directions from the oil streak patterns, and a comparison of the freestream streamlines and the wall flow streamlines. A review of corrections for direct force sensing shear meters for two-dimensional flows is presented with a brief discussion of their applicability to three-dimensional devices.
Evaluation of a Wall-Flow Direction Probe for Measurements in Separated Flows
Authors: Shivaprasad B. G. , Simpson R. L.
Published: October 2009

The upstream-downstream flow direction intermittency γpu is an important parameter that can quantitatively describe the stages of flow separation. This paper gives an improved design for a wall-flow-direction probe. Intermittency measurements made using this modified probe show agreement within experimental uncertainties with direct measurements made using a LDV, although both the unmodified and modified probe designs produce results that are consistently higher than those for the LDV.
Laminar Boundary Layer Near the Rotating End Wall of a Confined Vortex
Authors: Shakespeare W. J. , Levy E. K.
Published: October 2009

The results of an experimental and theoretical investigation of the fluid mechanics in a confined vortex are discussed with particular emphasis on behavior away from the axis of symmetry and near the end walls. The vortex is generated in a rotating cylindrical chamber with an exit opening in one end. Both end walls rotate. For the range of flow rates and swirl ratios (1≤S≤5) of interest here, the flow field far from the end walls behaves as inviscid and irrotational; and the end wall boundary layers are thin and laminar. Measurements and calculations of tangential and radial velocity in the end wall region show the development of a secondary flow resulting in a strong velocity “overshoot” in the radial component. Results illustrating the nature of the velocity variations on the end walls are presented; and it is shown that the mass flow rate through the end wall boundary layers, while only a small fraction of the total flow, increases with increasing swirl and with decreasing total flow rate through the chamber.
On the Analysis of Turbulent Boundary Layers on Slender Cylinders
Authors: Ackroyd J. A. D.
Published: October 2009

An earlier analysis of turbulent flow along a cylinder in a uniform stream by White is corrected. The analysis has been extended to include turbulent flow along a cylinder extruding through an orifice into a fluid at rest. The analyses are compared with the available data for drag and, except in the case of the cylinder extruding into a fluid at rest, the comparison is reasonably encouraging.
Plug Flow of Coarse Particles in a Horizontal Pipe
Authors: Tsuji Y. , Morikawa Y.
Published: October 2009

Plug flow of coarse particles was investigated experimentally in a horizontal pipe, in which a sub-pipe for secondary air injection was installed. Measurements were made about the plug motion, pressure drop, and transportation properties, and the roles of the main and sub-pipe air flow were clarified. The main air flow increases the number of plugs, while the sub-pipe air flow increases the plug velocity. The higher the main pipe air flow rate, the more regular the motion. The height of a stationary layer of deposited particles, which is built on the bottom of the main pipe, decreases with increasing the sub-pipe air flow rate. The pressure drop in the moving plug is quantitatively much smaller than that in the stationary packed bed of same particles.
Flow Behind Two Coaxial Circular Cylinders
Authors: Ko N. W. M. , Leung W. L. , Au H.
Published: October 2009

The flow behind two circular cylinders of different diameters, which were joined coaxially has been examined at the Reynolds number of 8 × 104. The detailed pressure spectral measurements indicate the shedding and the distributions of the pressure fluctuations of the vortex wakes associated with the big and small cylinders. The effect of the presence of the small vortex wake on the vortex shedding of the big cylinder and the interaction between them is presented. The wake formed behind the plane of discontinuity has been isolated and presented.
Measurements in a Motored Four-Stroke Reciprocating Model Engine
Authors: Arcoumanis C. , Bicen A. F. , Whitelaw J. H.
Published: October 2009

Measurements of ensemble-averaged axial and swirl velocities and the rms of the corresponding fluctuations obtained by laser-Doppler anemometry, are reported for the axisymmetric swirling flow in a four-stroke model engine motored at 200 rpm with a compression ratio of 3.5. A centrally located valve, incorporating a 60 degree seat angle and 30 degree swirl vanes resulting in a swirl number of 1.2, was used to draw in and exhaust seeded air. The piston-head configurations included a flat surface and a cylindrical bowl with and without a lip. Comparison of the results with those obtained previously, with a flat piston in the absence of compression, shows that the mean and rms profiles during the intake stroke are similar. In the axial plane a system of vortices is created which has almost disappeared by the time the inlet valve closes with a small vortex existing near the cylinder head at the early part of compression; later on this vortex breaks up and the mean velocities tend to become uniform. The intake generated turbulence decays gradually until the inlet valve closes; it then becomes uniform and remains constant in magnitude for the rest of the compression stroke. The mean swirl flow has a spiralling nature during intake but tends towards solid body rotation during compression with associated turbulence levels of similar magnitude to the axial ones. During the expansion stroke the rms velocities decrease further until the exhaust valve opens and new turbulence is generated. The influence of the piston bowl is generally small but the addition of a lip results, during the compression stroke, in inward movement of the air towards the bowl as the piston approaches TDC. The reverse squish effect, observed during the expansion stroke and due to the outgoing motion of the entrapped air inside the bowl, results in significant reversed velocities near the axis and increase in the turbulence levels close to the piston.
Review—Combined Measurements of Particle Velocities, Size Distributions, and Concentrations
Authors: Durst Franz
Published: October 2009

The present paper describes combined laser Doppler particle sizing systems which permit simultaneous velocity and size measurements of individual particles. Combined measurements of these properties are achieved by extended laser Doppler anemometers. These extensions require the physics of laser Doppler signal generation to be clarified. A system for measurements of small particles and one to measure the properties of large particles is described. Some applications of these instruments are given.
Diagnostic Measurements of Fuel Spray Dispersion
Authors: Tishkoff J. M. , Hammond D. C. , Chraplyvy A. R.
Published: October 2009

Plume shape, vaporization, droplet-size distribution, and number density of a solid-cone fuel spray were studied with both conventional and novel measurement techniques. Minor differences in spray plume shape were observed by measurements with photography, pulsed laser shadowgraphy, and in-line infrared spectroscopy. Laser Mie scattering showed the dispersion of small numbers of droplets beyond spray boundaries as determined by other measurements. A new optical method for nonintrusive, local, time-averaged measurement of vapor concentration, droplet-size distribution and number density within an axisymmetric spray is introduced. For the spray studied this method showed that vapor is confined to the spray plume and that vapor concentration and the concentration of small-diameter droplets exhibit analogous behavior.