bluuebunny/crossref_metadata_2025 huggingface dataset:
Queueing problems with two parallel servers
Authors: Chun Youngsub , Jeong Heo Eun
Published: May 2008

Agents are waiting for their jobs to be processed at a service facility. All agents need the same processing time but have different waiting costs per unit of time. The facility has two parallel servers and can serve two agents at a time. We are interested in finding the order in which to serve agents and the (positive or negative) monetary transfers they should receive. We introduce two rules, the “minimal transfer rule” and the “maximal transfer rule”. We show that they correspond to the Shapley (1953) values of associated queueing games, for two alternative definitions of the worth of a coalition. The two‐server queueing games correspond to the games similarly defined by Maniquet (2003) and Chun (2006a) for one server. If the worth of a coalition is defined by assuming that the coalitional members are served before the non‐coalitional members, then the minimal transfer rule is obtained. If it is defined by assuming that the coalitional members are served after the non‐coalitional members, then the maximal transfer rule is obtained.
Petty corruption: A game‐theoretic approach
Authors: Lambert‐Mogiliansky Ariane , Majumdar Mukul , Radner Roy
Published: May 2008

The paper explores a game‐theoretic model of petty corruption involving a sequence of entrepreneurs and a track of bureaucrats. Each entrepreneur's project is approved if and only if it is cleared by each bureaucrat. The project value is stochastic; its value is observed only by the entrepreneur, but its distribution is common knowledge. Each bureaucrat clears the project only if a bribe is paid. The bribe for qualified projects (“extortion”) and unqualified projects (“capture”) may differ. We identify the nature and welfare implications of different types of equilibria under appropriate technical assumptions on the structure of the game.
Negishi's contributions to the development of economic analysis: Research programs and outcomes
Authors: Young Warren
Published: May 2008

This paper surveys Negishi's significant contributions to economics and the research programs they have generated. In a series of papers and books, Negishi developed a number of models and methods of analysis that changed the course of modern economics and catalyzed research in areas that range from welfare and theoretical to applied and computable general equilibrium analysis, and the extension of imperfect competition to general equilibrium. trade theory and international economics. This paper shows that the Negishian research programs that emanated from his works are progressive, and still have an ongoing impact on mainstream economic analysis decades after their publication.
On Professor Takashi Negishi's contributions to economic theory
Authors: Grandmont Jean‐Michel , Nishimura Kazuo , Yano Makoto
Published: May 2008

Professor Takashi Negishi has made fundamental contributions to economic theory on an extremely broad range of topics. As the editors of this special issue, we feel extremely fortunate that each of us has worked on topics with respect to which Professor Negishi's influences have been particularly large. In this introductory article, each of us will discuss Professor Negishi's influence on the topic we are most familiar with. For the entire spectrum of his research, readers are referred to the list of Professor Negishi's publications presented at the end of this article.
Competitive fairness and the concept of a fair price under Delaware law on M&A
Authors: Yano Makoto
Published: May 2008

The entire fairness test that the Delaware Court of Chancery developed in the famous Technicolor case defines what constitutes fair dealings and fair pricing. This study introduces a new concept of fairness, called competitive fairness, that covers entire fairness. It develops what I call open market bargaining theory and demonstrates that the Technicolor outcome is an open market bargaining equilibrium, which can be thought as competitively fair under the nondiscrimination rule of markets.
Bifurcation and sunspots in the continuous time equilibrium model with capacity utilization
Authors: Benhabib Jess , Nishimura Kazuo , Shigoka Tadashi
Published: May 2008

In the present paper, we construct a continuous time model of economic growth with positive externalities and with variable capacity utilization, and study the global equilibrium paths in this model. If there is a homoclinic orbit or a periodic solution in this model, equilibrium is globally indeterminate. We show that positive externalities can yield multiple steady states, a one‐parameter family of homoclinic orbits, and a two‐parameter family of periodic solutions. It is also shown that there exists a sunspot equilibrium in this model.
The Lower River Roding Regeneration
Authors: Gray Joanna , Hawkes Jennifer , Martin Peter
Published: May 2008

The Lower River Roding Regeneration (LRRR) project was funded by the Office of the Deputy Prime Minister (ODPM) with a contribution from the Environment Agency and was charged with achieving environmental and social gains along the highly urbanised lower 4.4 km of the River Roding. The funding allowed £1.5 million for all elements of work within a 2‐year‐period. Of the four sites constructed, two allowed significant river restoration to be achieved: Creekmouth Open Space and Frogmore Frontage. In the former, an existing flood defence was set back to create a tidal backwater. In the latter, a concrete river wall was demolished and a graded riverbank was created. A total of 1 ha of new saltmarsh was created on these two sites. The project demonstrates how multiple objectives of river restoration, flood defence, habitat creation, improved public amenity and urban regeneration can be achieved in an industrial urban area.
Estimation of sewer leakage to urban groundwater using depth‐specific hydrochemistry
Authors: Rueedi J. , Cronin A. A. , Morris B. L.
Published: May 2008

The contribution of sewer leakage to urban groundwater recharge remains poorly characterised. There has been a tendency to focus on estimating leakage from pipe network characteristics rather than its impact on the receiving environment. Indeed, pipeline leakage simulation models are frequently used to analyse sewage systems and optimise maintenance efforts. Here a mass balance approach employing groundwater geochemistry is presented to estimate sewer leakage rates; this is done using depth‐specific groundwater quality measurements from multilevel monitoring piezometers, specially installed in the Sherwood Sandstone aquifer underlying Doncaster (UK). The results show that leakage rates from the foul sewage system are up to 10% of flow per annum (30–40% of urban recharge) and highlight the utility of groundwater quality monitoring (in particular depth‐specific sampling) as an alternative means to assess sewage ingress to urban groundwater.
The WFD dreams: between ecology and economics
Authors: Bouleau Gabrielle
Published: May 2008

The enactment of the Water Framework Directive (WFD) in the European Union (EU) triggers intense activity among Member States and raises some criticism. The good status of waters may include an ecological dream that is difficult to achieve. Moreover, criteria for derogations require strong economic arguments. This challenge raises the debate on whether the WFD is part of an incremental process, embedded in prior European water law, with feasible goals, or whether it is a dramatic change of policy towards an ecological dream that emerged during late negotiations, and therefore was hardly achievable. I will state that although the high ecological ambition of the WFD is unprecedented within the EU's water law, it has several precedents in other arenas, notably long enforced in the United States of America. I will argue that the major challenge of the directive is the combination of the ecological dream with an economic ideal, which has no equivalent in the United States.
Deconstructing public participation in the Water Framework Directive: implementation and compliance with the letter or with the spirit of the law?
Authors: Ker Rault Ph. A. , Jeffrey P. J.
Published: May 2008

This article offers a fresh reading of the Water Framework Directive (WFD) and of the Common Implementation Strategy guidance document number 8 on public participation (PP) aimed at identifying the conditions required for successful implementation. We propose that a central barrier to implementing Article 14 is that Integrated Water Resources Management (IWRM) problems are complex in character and that participation is a wicked process in practice. This article highlights some ambiguous interpretations of the WFD comparing and contrasting the ‘letter of the law’ and its ‘spirit’, based on a critical review of the nature of PP, who it concerns and when it takes place. First we articulate a complex system interpretation of IWRM in the context of the WFD. Second, we explain the difficulty to define blueprint for PP in IWRM. Finally, we present five interpretative challenging readings in order to highlight tensions between the ‘spirit’ and the ‘letter’ of the WFD.
Role of F4/80+Mac‐1high adherent non‐parenchymal liver cells in concanavalin A‐induced hepatic injury in mice
Authors: Mabuchi Ayako , Nagao Tomokazu , Koshio Osamu , Ishiwata Toshiyuki , Yano Akihiko , Suzuki Kazuo , Yokomuro Kozo , Wheatley Antony M.
Published: May 2008

Aim:  Non‐parenchymal liver cells (NPLC) play an important role in the regulation of immune responses and the inflammatory process. In this study, we hypothesized that F4/80+Mac‐1high+ cells were involved in the regulative feedback‐modulated regulation of inflammatory responses during concanavalin A (Con A)‐induced hepatitis.

Methods:  Hepatitis was induced in BALB/c mice by the intravenous injection of Con A. Liver injury was assessed using serum aminotransferase and pathology. The function of NPLC was assessed by FACS analysis. Accessory cell function of adherent Con A NPLC was performed with an ovalbumin specific T‐helper 1 (Th1) clone proliferation assay. The culture supernatant nitric oxide (NO) content was quantified by the Griess reaction. Inducible NO synthase (iNOS) expression was demonstrated by immunohistochemistry and Western blot analysis.

Results:  The number of hepatic F4/80+Mac‐1high+cells increased in a time‐dependent manner after Con A administration, which consequently suppressed Th1 cell proliferation by a mechanism likely to involve NO. The iNOS expression of NPLC was elevated at 24 h post‐Con A injection. In nude mice, F4/80+Mac‐1high+cells did not increase in the Con A‐treated liver; the NPLC did not suppress Th1 clone proliferation.

Conclusion:  These findings suggest that the in vivo activation of F4/80+Mac‐1high+cells by Con A administration suppresses Th1 cell proliferation by increasing NO, and subsequently reducing liver injury.
Rotordynamic Coefficients and Leakage Flow of Circumferentially Grooved Liquid-Seals
Authors: Kilgore J. J. , Childs D. W.
Published: May 2008

Measured leakage flow and rotordynamic coefficients for six, circumferentially-grooved, liquid seals are compared to predictions based on Nordmann et al.’s (1986) grooved seal model. The grooved seal model uses a modification of Hirs’ (1973) bulk-flow theory to account for the difference in friction factor in the circumferential and axial directions due to the grooves. Also, the model uses an average groove depth to account for the circumerential flow in the grooves. Comparison of the predicted and measured friction factors in grooved-seals with orbiting-rotors shows a poor correlation. In spite of the poor friction-factor correlation, the accuracy of predictions for rotordynamic coefficients are comparable to predictions of Childs et al. (1988) and Childs and Kim (1986) for smooth and hole pattern seals.
Calculation of Turbulent Flows in a Hydraulic Turbine Draft Tube
Authors: Agouzoul M. , Reggio M. , Camarero R.
Published: May 2008

A numerical method to simulate three-dimensional incompressible turbulent flows has been developed and applied to the calculation of various flow situations in a draft tube. The conservative form of the primitive-variable formulation of the Reynolds averaged Navier-Stokes equations, written for a general curvilinear co-ordinate system, is employed. An overlapping grid combined with opposed differencing for mass and pressure gradients is used. All the properties are stored at the center of the same computational cell which is used for mass and transport balances. The k–ε model is used to describe the turbulent flow. The boundary conditions for the turbulent properties are treated with a particular attention.
Using Viscous Calculations in Pump Design
Authors: Martelli F. , Michelassi V.
Published: May 2008

A viscous computer code for designing the meridional channels of high-performance pumps is presented. An averaging technique is used to reduce the three-dimensional flow to a two-dimensional model. The code, based upon an implicit finite difference method for steady two-dimensional incompressible flows, was validated in complex flow geometries prior to application in the design analysis of an actual pump. Viscous effects are taken into account by two different turbulence models. The Navier-Stokes solver is used in conjunction with a standard blade-to-blade calculation by means of an automatic graphic procedure that exchanges geometric and flowfield data. Various meridional shape solutions are presented and discussed in relation to physical evidence.
Pressure and Three-Component Velocity Measurements on a Diffuser That Generates Longitudinal Vortices
Authors: Goenka L. N. , Panton R. L. , Bogard D. G.
Published: May 2008

This paper presents flowfield measurements on a wide-angle, three-dimensional diffuser that has a vastly improved static-pressure recovery over the corresponding plane-wall diffuser when discharging into a plenum. The diffuser geometry consists of a pyramid-shaped insert attached to the diffuser expansion wall. The upsweep on the upper surface of the pyramid generates a transverse pressure gradient that causes the incoming flow to roll up into two symmetric, longitudinal vortices. Earlier flow-visualization studies have shown that these vortices replace the closed separated regions along the diffuser expansion wall, eliminating flow oscillations and hysteresis. This paper presents quantitative information, in the form of static pressure, total pressure, and three-component Laser Doppler Velocimeter (LDV) measurements, on the diffuser flowfield for two variations in the pyramid geometry. Information from these studies is useful in developing configurations with enhanced pressure recoveries. The greatly improved static-pressure recovery of this diffuser, combined with its superior flowfield features, make it particularly suitable for exhaust diffuser applications.
Macroscopic Wetting Behavior and a Method for Measuring Contact Angles
Authors: Katoh K. , Fujita H. , Sasaki H.
Published: May 2008

Macroscopic wetting behavior is investigated theoretically from a thermodynamic viewpoint. The axisymmetric liquid meniscus formed under a conical solid surface is chosen as the subject of the theoretical analysis. Using the meniscus configuration obtained by the Laplace equation, the total free energy of the system is calculated. In the case of the half vertical angle of the cone φ = 90 deg (horizontal plate), the system shows thermodynamic instability when the meniscus attaches to the solid surface at the contact angle. This result, unlike the conventional view, agrees well with the practical wetting behavior observed in this study. On the other hand, when 0 deg < φ < 90 deg, the system shows thermodynamic stability at the contact angle. However, when the solid cone is held at a position higher than the critical height from a stationary liquid surface, the system becomes unstable. It is possible to measure the contact angle easily using this unstable phenomenon.
Control of Surface Tension Flows: Instability of a Liquid Jet
Authors: Nahas N. M. , Panton Ronald L.
Published: May 2008

A technique of controlling surface tension flows using thermal radiation is proposed. This method takes advantage of the dependence on temperature of the surface tension forces to produce the desired controlling effects. In this research, a capillary water jet is taken as an example of a surface tension dominated flow. The ability to cancel a preexisting unstable perturbation is demonstrated. First an acoustical disturbance that dominates the naturally occurring perturbations is applied to the jet. This causes jet breakup at a shorter and constant distance from the orifice. Next, a CO2 laser beam, modulated at the same frequency as the primary disturbance, is focused on the surface of the jet. By proper adjustment of intensity and phase the two perturbations cancel each other and the natural breakup of the jet is recovered. The influences of phase and intensity mismatches were tested and are reported. In addition to its application to delaying breakup of capillary jets, this technique is a promising method of controlling both suface tension driven flows and instabilities in different industrial applications.
Experimental and Computational Study of Turbulent Flows in a Channel With Two Pairs of Turbulence Promoters in Tandem
Authors: Liou T.-M. , Chang Y. , Hwang D.-W.
Published: May 2008

Measurements and computations are presented of mean velocity and turbulence intensity for an arrangement of two pairs of turbulence promoters mounted in tandem in developing channel flow. The Reynolds number (ReD) and the pitch ratio (PR) were varied in the range of 1.2 × 104 to 1.2 × 105 and 1 to 100, respectively. The three pitch ratios 5, 10, 15 were found to provide three characteristic flows which are a useful test of the computational models. The effects of PR on the reattachment lengths and the pressure loss as well as the influence of ReD on the reattachment length were documented in detail. It was found that PR=10 was preferable to PR = 5 and PR = 15 from the standpoint of heat transfer enhancement.
Modal Analysis of Vibrations in Liquid-Filled Piping Systems
Authors: Lesmez M. W. , Wiggert D. C. , Hatfield F. J.
Published: May 2008

The motions of liquid-filled pipe reaches in which long wavelength assumptions are valid can be described by Poisson-coupled axial stress waves in the pipe and in the liquid column, and in the piping structure, by torsional and flexural waves. Based on linearized assumptions, a simultaneous solution of the wave equations is presented. Eigenvalues and mode shapes are derived for the variables fluid pressure and displacements, and pipe forces and displacements. The results are assembled into a transfer matrix, which represents the motion of a single pipe section. Combined with point matrices that describe specified boundary conditions, an overall transfer matrix for a piping system can be assembled. Corresponding state vectors can then be evaluated to predict the piping and liquid motion, and the accompanying forces. The results from two experimental piping systems are compared with the ones obtained by the modal analysis method.
Flow Regulation Characteristics of Thin-Walled Compliant Tubes: Part I—Theoretical Analysis
Authors: Kececioglu Ifiyenia
Published: May 2008

The objective of this investigation is the study of the flow limitation behavior of thin-walled compliant tubes for the design of a flow regulator employing a collapsible tube as its active element. In this paper, the theoretical basis is set up for the high-Reynolds-number wave-speed flow regulation and the low-Reynolds-number frictional flow regulation behaviors of thin-walled compliant tubes. In Part II of this paper [1], experimental results and design criteria are provided in support of the analytically derived characteristic flow regulation curve for the wave-speed flow regulator.
Flow Regulation Characteristics of Thin-Walled Compliant Tubes: Part II—Experimental Verification and Design of the Wave-Speed Flow Regulator
Authors: Kececioglu Ifiyenia
Published: May 2008

The theoretical foundation of the two different mechanisms of compliant-tube flow limitation when the flow is either friction dominated (frictional flow limitation for low-Reynolds-number flow) or inertia dominated (wave-speed flow limitation for high-Reynolds-number flow) was formulated in Part I [1] of this paper. In this part of the paper, the high-Reynolds-number wave-speed flow limitation behavior of compliant tubes is verified experimentally and applied to the design of a flow regulator employing a collapsible tube as its active element. Criteria for the design of an inertia-dominated compliant-tube flow regulator are established and checked against findings of experiments.
The Hydrodynamic Tunnel of I.M.G.: Former and Recent Equipments
Authors: Brianc¸on-Marjollet L. , Michel J. M.
Published: May 2008

The I.M.G. Hydrodynamic Tunnel is described in its initial state and with successive equipments that improved its performances. Particular attention is given to the recent nuclei control system.
Solid Phase Contribution in the Two-Phase Turbulence Kinetic Energy Equation
Authors: Abou-Arab T. W. , Roco M. C.
Published: May 2008

This paper presents a multiphase turbulence closure employing one transport equation, namely, the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A double-time averaging approach for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less restrictive assumptions comparative to the previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.
The Plane Poiseuille Flow of a Particle-Fluid Mixture
Authors: Drew D. A.
Published: May 2008

The “laminar” shear flow of a particle-fluid mixture is studied using the two-fluid model, which is based on equations of conservation of mass and momentum for each material. The equations are applied to plane parallel flow, where the equations or mixture axial momentum and an equation for the concentration across the channel are derived. An asymptotic solution to the equations is derived which shows that the particles move to the center of the channel, forming a core which does not shear. The core is surrounded by clear fluid layers where all the shear occurs.
Turbulent Shear Flow Over Surface Mounted Obstacles
Authors: Schofield W. H. , Logan E.
Published: May 2008

The mean flow field surrounding obstacles attached to a wall under a turbulent boundary layer is analyzed. The analysis concentrates on how major features of the flow are influenced by model geometry and the incident shear flow. Experimental data are analyzed in terms of nondimensionalized variables chosen on the basis that their effect on major flow features can be simply appreciated. The data are restricted to high Reynolds number shear layers thicker than the attached obstacle. The work shows that data from a wide range of flows can be collapsed if appropriate nondimensional scales are used.
Turbulent Boundary-Layer Development Around a Square-Sectioned U-Bend: Measurements and Computation
Authors: Iacovides H. , Launder B. E. , Loizou P. A. , Zhao H. H.
Published: May 2008

A computational and experimental study is reported of turbulent flow around a square-sectioned U-bend with a mean bend radius equal to 3.375 times the hydraulic diameter (DH): the duct Reynolds number is 58,000. The bend geometry is the same as that for which Chang et al. (1983) have reported extensive LDA data except that in the latter experiment the bend was preceded by some thirty hydraulic diameters of straight ducting (thus the boundary layers filled the duct). In the present case, with the inlet section shortened to only 6 DH, the boundary layer thickness at inlet to the bend was only about 0.15 DH. Despite the thinner boundary layers a strong secondary flow is generated which, by 135° around the bend, appears to have broken down into a chaotic pattern. Computations of the flow using a three-dimensional finite-volume solver employing an algebraic second-moment (ASM) turbulence model are in generally close agreement with the experimental data and suggest that the secondary flow, in fact, breaks down into a system of five eddies on either side of the mid-plane, in place of the classical single vortex structure.
Scaling Turbulent Wall Layers
Authors: Panton Ronald L.
Published: May 2008

The two-layer concept is a framework for interpreting events and constructing mathematical models of turbulent wall layers. In this paper an asymptotic theory is constructed employing the idea that the interaction between the layers is the most important aspect. It is shown that the matching process for the layers can be used to define a characteristic scale, u*, and to produce an equation that relates u* to the known parameters; U∞, v, h, e, and dp/dx. At infinite Reynolds number the scale u* is equal to uτ, the friction velocity, but they are distinct at moderate Reynolds numbers. The theory produces very simple results. For instance, the overlap velocity laws are logarithmic with an invariant von Ka´rma´n constant; at low Reynolds numbers the additive constant changes while the slope remains the same. The effect of low Reynolds numbers on the Reynolds stress in the overlap layer is also analyzed. A composite expansion explains the strong Reynolds number effect on the stress profiles. This occurs because the mixing of outer and inner layer phenomena take place at different locations as the size of the overlap region changes. The location of the maximum Reynolds stress is given by y+max = (Re/k)1/2. The overlap region was not found to be a region of constant stress, as put forth in many heuristic arguments.
A One-Parameter Integral Method for Turbulent Transpired Boundary Layer Flow
Authors: Thomas L. C. , Kadry H. M.
Published: May 2008

This paper presents the development of a practical one-parameter integral method for transpired turbulent boundary layer flow. The method involves the use of one-parameter polynomial approximations for total stress and the solution of the familiar integral momentum equation. The method is compared with experimental data and numerical solutions for a range of near equilibrium boundary layers.
Quasi-Steady Discharge of Fluid From a Vessel Through a Poppet Valve
Authors: Chu S. S. , Miller S. K. , Chow W. L.
Published: May 2008

Previously established characteristics of steady-state discharge through a valve are employed for the study of quasi-steady discharge from a vessel. Experimental examination of the problem has also been carried out. The data obtained in the laboratory fully supported the validity of the quasi-steady approach to this type of unsteady flow problems.
Interference Drag of a Turbulent Junction Vortex
Authors: Pierce F. J. , Nath S. K.
Published: May 2008

The interference drag identified with the junction of a streamlined cylindrical body and a flat plate was investigated. The junction drag was calculated from a set of detailed, self consistent, high quality data using a control volume approach. The drag for the isolated flat plate and streamlined cylinder making up the junction was calculated using boundary-layer solvers together with surface pressure measurements. For the particular and relatively thick body under consideration, the results show a significant increase in drag due to the junction. These and other available results indicate that the interference drag has a systematic dependence on the thickness to chord ratio. The junction vortex wake increases the downstream flat plate drag significantly. Because of this effect, a unique value for the drag force, drag coefficient, or induced drag coefficient for a junction vortex flow would require that the geometry be specified in detail. The induced drag and the total pressure losses identified with the junction are also reported.
Prediction of Airflow With Swirl in Perforated Polyethylene Tubes
Authors: Brundrett E.
Published: May 2008

The influence upon flow of fan induced inlet swirl is examined for two commonly used sizes of uniformly perforated polyethylene ventilation tubes (polytubes). Swirl is present at the inlet of most polytubes that are directly connected to a supply fan whether or not an antiswirl device is used. Four experimentally obtained inlet swirl angles are examined using swirl modified pressure recovery coefficients, pipe friction factors, and orifice discharge equations. A computational procedure divides the polytube into five equal length segments to obtain a rapid yet acceptably accurate procedure. An iterative microcomputer spreadsheet solves the resulting set of simultaneous equations, providing pressure and flow discharge profiles along the tube that are in very good agreement with the experimental data and with the data of others. An extension of the analysis for uniformly spaced orifices indicates that supply swirl angles greater than 25 deg and large length to diameter ratios should be avoided.
Nonideal Isentropic Gas Flow Through Converging-Diverging Nozzles
Authors: Bober W. , Chow W. L.
Published: May 2008

A method for treating nonideal gas flows through converging-diverging nozzles is described. The method incorporates the Redlich-Kwong equation of state. The Runge-Kutta method is used to obtain a solution. Numerical results were obtained for methane gas. Typical plots of pressure, temperature, and area ratios as functions of Mach number are given. From the plots, it can be seen that there exists a range of reservoir conditions that require the gas to be treated as nonideal if an accurate solution is to be obtained.
Coherent Structures in a Three-Dimensional Wall Jet
Authors: Matsuda Hisashi , Iida Sei-ichi , Hayakawa Michio
Published: May 2008

The formation mechanism of streamwise vortices in the near field of the three-dimensional wall jet discharging from a circular nozzle along a flat plate is studied experimentally using a conditional sampling technique. Ensemble-averages of the lateral velocity component indicate the presence of large-scale horseshoe-like structures, whose legs are inclined and stretched to form the streamwise vortices in the mixing region of the jet. Based on the present result, a coherent structure model for the near field of the wall jet is proposed.
Flow in a Channel With a Time-Dependent Indentation in One Wall
Authors: Ralph M. E. , Pedley T. J.
Published: May 2008

Computations and flow visualization experiments have been carried out on 2-D flow in a channel, with an indentation in one wall that can move in and out. There is plane Poiseuille flow upstream and attention is focussed on the flow downstream of the indentation. Four time-courses of indentation motion are examined: I oscillation between a flush and an indented postion; II advance from flush to indented, after which it remains stationary; III retraction to flush from a steady indentation; IV small amplitude oscillation about a substantially indented position. Various values of Reynolds number, Re, and Strouhal number, St, are employed (250≤Re≤911; 0.01≤St≤0.1). The results show that (a) vorticity waves and eddies are generated in cases I and II (as in reference [11]); (b) in case II at higher experimental Re the flow does not become steady because the steady flow is unstable to a Rayleigh wave, on the shear layer bounding the main separation region, whose wavelength is significantly less than that of the vorticity wave; (c) in case III the waves that are generated at each parameter set seem to be Rayleigh waves not vorticity waves; (d) in case IV short waves give way to longer waves whose amplitude is comparable with the mean indentation height not the oscillation amplitude. Although resembling vorticity waves these do not propagate like the forced waves of case I and presumably represent a nonlinear interaction between Rayleigh waves, vorticity waves, and the very long, weak waves present even in steady flow. Further downstream, in many cases, the 2-D waves break down into turbulence via 3-D disturbances.
A Model for the Low to Moderate Speed Performance of the Rotating Disk Skimmer
Authors: Christodoulou M. S. , Turner J. T. , Wilson S. D. R.
Published: May 2008

In an extensive experimental investigation (Christodoulou, 1985) the performance of a disk skimmer rotating in the vertical plane and partially immersed in a liquid has been studied. The aim of the study was to examine the physical and hydrodynamic parameters governing the oil collection rate of the disk when used as one element of a rotating disk skimmer, a device commonly employed to recover oil and similar immiscible liquids from a water surface. This paper presents a theoretical solution for the flow field set up by the disk which has led to an improved understanding of the hydrodynamics of the disk drag-out problem at low to moderate speeds. Experimental data are presented and compared with the theoretical solutions: discrepancies are then explained in terms of departures from the original assumptions.
Interaction of Liquid Droplets With Planar Shock Waves
Authors: Yoshida T. , Takayama K.
Published: May 2008

Interactions and breakup processes of 1.50-mm-diameter ethyl alcohol droplets and 5.14-mm-diameter water bubbles with planar shock waves were observed using double-exposure holographic interferometry. Experiments were conducted in a 60 mm × 150 mm cross-sectional shock tube for shock Mach number 1.56 in air. The Weber numbers of droplets and liquid bubbles were 5.6 × 103 and 2.9 × 103, respectively, while the corresonding Reynolds numbers were 4.2 × 10 and 1.5 × 105. It is shown that the resulting holographic interferogram can eliminate the effect of the mists produced by the breakup of the droplets and clearly show the structure of a disintegrating droplet and its wake. This observation was impossible by conventional optical flow visualization. It is demonstrated that the time variation of the diameter of a breaking droplet measured by conventional optical techniques has been overestimated by up to 35 percent.
A Generalized Approach on Equilibrium Theory of Cavitation Nuclei in Liquid-Gas Solutions
Authors: Tsai Jing-Fa , Chen Yih-Nan
Published: May 2008

The availability of a single bubble-droplet system is derived from energy conservation and the principle of entropy. The equilibrium and critical conditions are determined by minimizing the availability without any assumption on the volume of the bubble-droplet system. It is found that the compressibility effect of the liquid-gas solution can be neglected in such a small bubble-droplet system and dilute solution condition. The results of the present analyses confirm previous conclusions reached by Cha that a bubble can remain in a state of stable equilibrium provided that the ratio of the total number of moles of gas to the total number of moles of the liquid is not extremely small and the external pressure falls between a dissolution limit and a cavitation limit.
The Near Wake Characteristics of Cavitating Bluff Sources
Authors: Ramamurthy A. S. , Balachandar R.
Published: May 2008

The influence of cavitation on vortex shedding behind constrained sharp-edged bluff prisms is studied experimentally. At a given blockage, the length of the vortex formation region is found to increase as the cavitation number of the flow is reduced. The vortex appears to be stabilized from breaking up in the partially cavitating regime of flow. Test results indicate that the separation velocity is the proper velocity scale to reduce or eliminate blockage effects.
Complex Wavespeed and Hydraulic Transients in Viscoelastic Pipes
Authors: Suo Lisheng , Wylie E. B.
Published: May 2008

The classic formula for waterhammer wavespeed is extended to calculate the complex-valued, frequency-dependent wavespeed in a viscoelastic pipe, which takes into account the effect of viscoelasticity of pipe wall material on wave propagation. With the complex wavespeed, the standard impedance or transfer matrix is directly used to analyze resonating conditions in systems including viscoelastic pipes, and the impulse response method presented previously by the authors is applied to compute nonperiodic transients. Numerical results are compared with experimental data and good agreement is observed.
Navier–Stokes Simulation of Transonic Blade-Vortex Interactions
Authors: Liu N.-S. , Davoudzadeh F. , Briley W. R. , Shamroth S. J.
Published: May 2008

Transonic strong blade-vortex interaction is numerically analyzed by solving the unsteady 2-D Navier–Stokes equations using an iterative implicit second order scheme. The dominant processes during the interaction are the development of large transverse pressure gradients in the upper leading edge region and the development of disturbances at the root of the lower surface shock wave. As a result of this interaction, high pressure pulses are emitted from the leading edge, and acoustic waves are radiated from the lower surface in a region originally occupied by a supersonic pocket. In addition, severe load variations occur when the vortex is within one chord length of the blade.
Application of an Implicit Relaxation Method Solving the Euler Equations for Time-Accurate Unsteady Problems
Authors: Brenneis A. , Eberle A.
Published: May 2008

A numerical procedure is presented for computing time-accurate solutions of flows about two and three-dimensional configurations using the Euler equations in conservative form. A nonlinear Newton method is applied to solve the unfactored implicit equations. Relaxation is performed with a point Gauss-Seidel algorithm ensuring a high degree of vectorization by employing the so-called checkerboard scheme. The fundamental feature of the Euler solver is a characteristic variable splitting scheme (Godunov-type averaging procedure, linear locally one-dimensional Riemann solver) based on an eigenvalue analysis for the calculation of the fluxes. The true Jacobians of the fluxes on the right-hand side are used on the left-hand side of the first order in time-discretized Euler equations. A simple matrix conditioning needing only few operations is employed to evade singular behavior of the coefficient matrix. Numerical results are presented for transonic flows about harmonically pitching airfoils and wings. Comparisons with experiments show good agreement except in regions where viscous effects are evident.
Flow Through an Orifice From a Transverse Stream
Authors: Andrews K. A. , Sabersky R. H.
Published: May 2008

Flow through orifices has been investigated thoroughly and a large amount of information on discharge coefficients and losses is available. Almost all of these results presuppose that the approaching flow is symmetrical in respect to the orifice. Very little information, however, is available for flows such as those through an orifice located in the wall of a pipe which itself carries a fluid. The present investigation consists of a set of exploratory experiments to obtain discharge coefficients for this kind of orifice flows and, in particular, to ascertain the effect of the velocity in the pipe on these coefficients.
Review—Mechanisms of Cavitation Inception
Authors: Rood E. P.
Published: May 2008

A review is made of progress in research during the period 1979–1989 on the fundamental physical mechanisms of hydrodynamic cavitation inception. During that decade identification of the physical phenomena has been made, and techniques have been developed to reproduce on laboratory scale selected forms of full scale cavitation inception. Understanding of the mechanisms remains shallow, and analytical/numerical prediction methods are nonexistent except for the restricted case of travelling bubble cavitation inception in a passive pressure field. The control of inception is seen to be related in part to control of the underlying viscous flow features. A growing body of experimental evidence points to microscale vortex cavitation as a primal inception event.
Laminar Flow Past Colinear Spheres With Fluid Injection
Authors: Chiang H. , Kleinstreuer C.
Published: May 2008

A validated computer simulation model has been developed for the analysis and design of colinear porous sphere systems in a convective stream. Using a modified and extended finite element software package, the steady-state Navier-Stokes equations have been solved describing laminar axisymmetric flow past closely spaced monodisperse spheres with fluid injection. Of interest are the coupled nonlinear interaction effects on the fluid flow patterns and ultimately on the drag coefficient of each sphere for different free stream Reynolds numbers (20 ≤ Re ≤ 200) and intersphere spacings (1.5 ≤ dij ≤ 6.0) in the presence of fluid injection (0 ≤ vb ≤ 0.1). At small spacings and low Reynolds numbers, fluid injection causes earlier flow separation while for Re ≥ 100 surface blowing is more influential in altering the recirculation zones between spheres and thickening the boundary layers. As a result, the total drag of each sphere decreases with increasing blowing intensity although the pressure or form drag of the first sphere may increase at small spacings.
An Optimum Suppression of Fluid Forces by Controlling a Shear Layer Separated From a Square Prism
Authors: Sakamoto H. , Tan K. , Haniu H.
Published: May 2008

This paper deals with the suppression of the fluid forces by controlling a shear layer on one side separated from a square prism. The control of the separated shear layer was established by setting up a small circular cylinder (the control cylinder) in it on one side. Experimental data were collected to examine the effects on the fluid forces and vortex shedding frequency due to variation of the position and diameter of the control cylinder. The results show that (i) the maximum reduction of the time-mean drag and fluctuating lift and drag occurred when the control cylinder was located near what would ordinarily be considered the outer boundary of the shear layer; (ii) the control of the separated shear layer by means of a small cylinder appeared to be effective in suppressing the fluctuating lift and drag rather than the time-mean drag; (iii) in the case of the control cylinder of 6 mm in diameter, the time-mean drag was reduced to about 30 percent, and the fluctuating lift and drag were reduced to approximately 95 and 75 percent, respectively; (iv) the fluid forces and the frequency of vortex shedding of the square prism were mainly dependent on the characteristics of a very thin region near the outer boundary of the shear layer.
Numerical Computation of Laminar Separation and Reattachment of Flow Over Surface Mounted Ribs
Authors: Hong Ying-Jong , Hsieh Shou-Shing , Shih Huei-Jan
Published: May 2008

Numerical results are presented concerning the fluid characteristics of steady-state laminar flow over surface mounted ribs. Computations are carried out using a false transient stream function-vorticity form. The effects of the aspect ratios (width-to-depth) of the ribs and Reynolds numbers as well as initial boundary-layer thickness on entire flow field, separated region, and reattachment length are presented and discussed. The computed reattachment distance compares reasonably well with those data reported by previous studies. A correlation is provided in terms of the rib aspect ratio, Reynolds number, and the ratio of boundary-layer thickness and rib height. The pressure drop is excessive along the upstream vertical step face and it recovers thereafter, which agrees qualitatively with those of the previous studies for the flow over backward-facing steps.
A Numerical Analysis of Pulsating Laminar Flow Through a Pipe Orifice
Authors: Jones E. H. , Bajura R. A.
Published: May 2008

A study of laminar pulsating flow through a 45 degree bevel pipe orifice was performed using finite-difference approximations to the governing stream function and vorticity transport equations. The distance from (−∞) to (+∞) was transformed into the region from (−1) to (+1) for the streamwise coordinate. Solutions were obtained for orifice bore/pipe diameter ratios of 0.2 and 0.5 for bore Reynolds numbers in the range from 0.8 to 64 and Strouhal numbers from 10−5 to 102. Stream and vorticity function plots were generated for all cases and the time-dependent discharge coefficient waws computed and averaged over a cycle of pulsation. The numerical solutions agree closely with available experimental data for steady flow discharge coefficients. The results show that the effects of pulsation on the discharge coefficient can be correlated by using the product of the orifice bore Reynolds and Strouhal numbers.
Intermittent Phenomena in the Flow Over a Rib Roughened Surface
Authors: Mullin T. , Martin S. R.
Published: May 2008

Laser Doppler anemometry has been used to make measurements of a small recirculation bubble in a turbulent water flow over a rib roughened surface. The bubble occurs near the leading edge of a transverse rib which is a model of the ribbed surface used to enhance cooling on nuclear reactor fuel pins. The bubble is transient, and spectral and correlation measurements were made to investigate any periodicity. It was found that the bubble itself did not show any periodicity but there was evidence for fluctuations in the main stream with a Strouhal number of 0.1.
Numerical Analysis of Turbulent Flow in a Two-Dimensional Nonsymmetric Plane-Wall Diffuser
Authors: Yuan Mingshun , Song Charles C. S. , He Jianming
Published: May 2008

By solving weakly compressible flow equations with application of Smogrinsky’s subgrid-scale turbulent model and partial-slip condition at the wall, a two-dimensional analysis is made on the flow of Re = 1.2 × 106 in a nonsymmetric planewall diffuser. The calculated velocity profiles are compared with the measured data, and the effect of inlet and outlet conditions on diffuser performance is evaluated. Comparison is also made between the symmetric and non-symmetric plane-wall diffusers.
A Numerical Investigation of the Turbulent Flow Field Generated by a Stationary Cube
Authors: Raul R. , Bernard P. S.
Published: May 2008

The turbulent flow field generated by a stationary cube at Reynolds numbers 2000 and 14,000 is investigated numerically. A vorticity-vector potential formulation of the equations of motion is employed. Turbulence effects are accounted for through the use of a vorticity transport closure scheme in which dynamical equations for vorticity mean and covariance are supplemented by a kinematic equation for turbulent kinetic energy. Semi-implicit finite difference approximations to the equations of motion are solved iteratively by a vectorizable 8-color SOR algorithm. The numerical mesh is designed so that the turbulent flow field can be computed down to solid surfaces without the use of wall functions. The properties of the computed flow field, including drag, axial velocity, separation points, and three-dimensional flow structure show good agreement with experimental observations of similar bluff body flows.
Further Experiments on Transition to Turbulence in Constant-Acceleration Pipe Flow
Authors: Lefebvre P. J. , White F. M.
Published: May 2008

A second series of experiments was conducted to extend and validate recently reported data by the present authors on transition to turbulence in pipe flows started from rest under constant acceleration. The test section diameter was increased from the 5 cm of the previous experiment to 9 cm for the present study. The low end of the acceleration range was also extended by an order of magnitude from 1.8 m/s2 down to 0.2 m/s2. The highest acceleration was 11.2 m/s2. Pipe Reynolds number at transition was observed to be as high as 1.1 × 106. The present results are shown to validate the previously suggested transition correlation parameters. An analysis based on an empirical equation for transition in convectively accelerated flows is extended and applied to the current experimental data.