bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Computation of Flow in a Passage With 360-Degree Turning and Multiple Airfoils
Authors: Shyy W. , Vu T. C.
Published: May 2008

The spiral casing of a hydraulic turbine is a complex flow device which contains a passage of 360-degree turning and multiple elements of airfoils (the so-called distributor). A three-dimensional flow analysis has been made to predict the flow behavior inside the casing and distributor. The physical model employs a two-level approach, comprising of (1) a global model that adequately accounts for the geometry of the spiral casing but smears out the details of the distributor, and represents the multiple airfoils by a porous medium treatment, and (2) a local model that performs detailed analysis of flow in the distributor region. The global analysis supplies the inlet flow condition for the individual cascade of distributor airfoils, while the distributor analysis yields the information needed for modeling the characteristics of the porous medium. Comparisons of pressure and velocity profiles between measurement and prediction have been made to assess the validity of the present approach. Flow characteristics in the spiral casing are also discussed.
Real Gas Effects for Compressible Nozzle Flows
Authors: Drikakis D. , Tsangaris S.
Published: May 2008

Numerical simulation of compressible nozzle flows of real gas with or without the addition of heat is presented. A generalized real gas method, using an upwind scheme and curvilinear coordinates, is applied to solve the unsteady compressible Euler equations in axisymmetric form. The present method is an extension of a previous 2D method, which was developed to solve the problem for a gas having the general equation of state in the form p = p(ρ, i). In the present work the method is generalized for an arbitrary P-V-T equation of state introducing an iterative procedure for the determination of the temperature from the specific internal energy and the flow variables. The solution procedure is applied for the study of real gas effects in an axisymmetric nozzle flow.
On the Main Flow Pattern in Hydrocyclones
Authors: Hwang C. C. , Shen H. Q. , Zhu G. , Khonsari M. M.
Published: May 2008

A theoretical model is developed for the prediction of the main flow pattern in hydrocyclones. The model regards the main body of the cyclone as inviscid and includes provisions for the fluid underflow in cyclones. The governing equations are solved analytically in closed form. To verify the results, a laboratory-scale conically-shaped hydrocyclone was designed, built, and tested. Experimental measurements for axial and tangential velocities are presented with a series of tests solely devoted to the effect of underflow. The theoretical and experimental results are shown to be in good agreement. It is concluded that such an inviscid model gives an adequate representation of the main flow field in a cyclone.
Numerical Uncertainty in Fluid Flow Calculations: Needs for Future Research
Authors: Celik Ismail
Published: May 2008

Computational fluid dynamics (CFD) has established itself as a viable technique for performing research and solving engineering problems, and when used correctly, can give accurate results for many fairly complex problems. This success has led to an ever increasing number of journal publications, many code developers, and surprisingly many users in the industry. Commercial CFD packages are often marketed by claiming that a particular code can solve almost every fluid flow problem, while many users, both in industry and academia, stand aloof from quantitative error measures, instead being dazzled by colorful computer generated output. This is mostly due to insufficient education in the scientific computing discipline which often leads (intentional or not) to misuse and wrong conclusions. Every year, hundreds of papers are published in conference proceedings, and journals, on the advancement and application of CFD techniques. Whenever something is spawned in such large quantities it is very easy to lose sense of quality control. To assert quality, papers often end with a conclusion such as “good agreement is found between experiments and predictions” to which the readers have become so immune that it no longer has meaning. Unfortunately, very little information is provided about the numerical uncertainty and the experimental data are often treated as if they are 100 percent accurate.
The Combined Drag Effects of Riblets and Polymers in Pipe Flow
Authors: Anderson G. W. , Rohr J. J. , Stanley S. D.
Published: May 2008

The additional skin friction effect produced by a 3M riblet surface, used in conjunction with low concentration polymer solutions, is investigated in fully developed, turbulent pipe flow. Generally at the low concentrations of Polyox 301 and guar gum studied, the absolute drag reduction of the 3M riblets appears to be independent of the polymer presence, with a maximum between 5 and 7 percent occurring around h+ = 12. Comparisons with previous polymer studies with 3M riblets, sand roughened and commercially rough surfaces are made.
Prediction of Pressure Drop for Incompressible Flow Through Screens
Authors: Brundrett E.
Published: May 2008

A new pressure loss correlation predicts flow through screens for the wire Reynolds number range of 10−4 to 104 using the conventional orthogonal porosity and a function of wire Reynolds number. The correlation is extended by the conventional cosine law to include flow that is not perpendicular to the screen. The importance of careful specification of wire diameter for accurate predictions of porosity is examined. The effective porosity is influenced by the shape of the woven wires, by any local damage, and by screen tension.
Vortex Shedding and Lock-On in a Perturbed Flow
Authors: Hall Mary S. , Griffin Owen M.
Published: May 2008

Vortex shedding resonance or lock-on is observed when a bluff body is placed in an incident mean flow with a superimposed periodic component. Direct numerical simulations of this flow at a Reynolds number of 200 are compared here with experiments that have been conducted by several investigators. The bounds of the lock-on or resonance flow regimes for the computations and experiments are in good agreement. The computed and measured vortex street wavelengths also are in good agreement with experiments at Reynolds numbers from 100 to 2000. Comparison of these computations with experiments shows that both natural, or unforced, and forced vortex street wakes are nondispersive in their wave-like behavior. Recent active control experiments with rotational oscillations of a circular cylinder find this same nondispersive behavior over a three-fold range of frequencies at Reynolds numbers up to 15,000. The vortex shedding and lock-on resulting from the introduction of a periodic inflow component upon the mean flow exhibit a particularly strong resonance between the imposed perturbations and the vortices.
Measurement and Calculation of Fluid Dynamic Characteristics of Rough-Wall Turbulent Boundary-Layer Flows
Authors: Hosni M. H. , Coleman H. W. , Taylor R. P.
Published: May 2008

Experimental measurements of profiles of mean velocity and distributions of boundary-layer thickness and skin friction coefficient from aerodynamically smooth, transitionally rough, and fully rough turbulent boundary-layer flows are presented for four surfaces—three rough and one smooth. The rough surfaces are composed of 1.27 mm diameter hemispheres spaced in staggered arrays 2, 4, and 10 base diameters apart, respectively, on otherwise smooth walls. The current incompressible turbulent boundary-layer rough-wall air flow data are compared with previously published results on another, similar rough surface. It is shown that fully rough mean velocity profiles collapse together when scaled as a function of momentum thickness, as was reported previously. However, this similarity cannot be used to distinguish roughness flow regimes, since a similar degree of collapse is observed in the transitionally rough data. Observation of the new data shows that scaling on the momentum thickness alone is not sufficient to produce similar velocity profiles for flows over surfaces of different roughness character. The skin friction coefficient data versus the ratio of the momentum thickness to roughness height collapse within the data uncertainty, irrespective of roughness flow regime, with the data for each rough surface collapsing to a different curve. Calculations made using the previously published discrete element prediction method are compared with data from the rough surfaces with well-defined roughness elements, and it is shown that the calculations are in good agreement with the data.
Effects of a Large Eddy Breakup Device on the Fluctuating Wall Pressure Field (Data Bank Contribution)
Authors: Keith W. L. , Barclay J. J.
Published: May 2008

Wall pressure spectra and mean velocity profiles were measured with and without a large eddy breakup device (LEBU) located upstream in high Rθ turbulent boundary layers. Changes of the order of 5 percent occurred in the mean wall shear stress. The wall pressure spectra of the manipulated flow did not show the existence of any highly energized coherent structures, but rather moderate changes occurring over broad frequency ranges. Reductions in the wall pressure autospectra occurred at lower frequencies associated with turbulence activity in the outer layer and the outer portion of the log law layer. Increases occurred at higher frequencies associated with the inner portion of the log law layer. The changes in the wall pressure coherence levels were similar, but generally more complex with greater spatial persistence. The changes in both the autospectra and coherence indicate a conversion of energy from lower to higher convective wavenumbers.
Study of Nuclei Distribution and Vortex Diffusion Influence on Nuclei Capture by a Tip Vortex and Nuclei Capture Noise
Authors: Ligneul P. , Latorre R.
Published: May 2008

Earlier studies of cavitation nuclei behavior in the presence of a Rankine tip vortex have shown that the nuclei is attracted or captured by the vortex pressure field and during this process noise is produced by the rapid nuclei growth. The present paper extends the study of Ligneul and Latorre (1989). The capture of nuclei by the tip vortex was characterized by an index M which depends on the nuclei radius, initial location, and the vortex circulation. To clarify the nuclei distribution effected by this capture process, the frequency of nuclei capture is derived in terms of the nuclei distribution N(R). The influence of the tip vortex axial diffusion on the nuclei capture process is formulated and number results presented to show how vortex diffusion delays the nuclei capture. The paper closes with a discussion of the numerical simulation of the nuclei capture and noise generation by the tip vortex.
Pressure Measurements Around a Rotating Cylinder With and Without Crossflow
Authors: Tawfek A. A. , Prasad B. V. S. S. S. , Mohanty A. K.
Published: May 2008

Static pressure measurements around a cylinder rotating about an orthogonal axis with and without superimposed crossflow are carried out by using a capacitance type differential pressure transducer in conjunction with a slip-ring apparatus. A coefficient of pressure (Cp) is defined for the rotating cylinder and typical variations of Cp along its length and periphery are presented.
Perspective: Unsteady Wing Theory—The Ka´rma´n/Sears Legacy
Authors: McCune J. E. , Tavares T. S.
Published: May 2008

The aerodynamic analysis of wings and their vortex wakes is discussed from a perspective of its relation to the 1938 work of Ka´rma´n and Sears. The key concepts from this early paper on the analysis of airfoils in small amplitude unsteady motion are reviewed. These concepts are then used as a point of departure for developing techniques for calculating and interpreting the aerodynamic characteristics of both airfoils in large amplitude motion with deforming vortex wakes, and maneuvering low-aspect-ratio wings with leading-edge separation. Calculated examples are presented for this extended set of applications, and are compared to related analyses and experiments.
Eigen-Functions of Linearized Unsteady Boundary Layer Equations
Authors: Lam S. H. , Rott N.
Published: May 2008

The Lam and Rott theory of linearized unsteady boundary layers is revisited, and some new results are obtained. The exact outer eigen-solution for a flat plate found in the original paper is shown to be a special case of the Prandtl-Glauert transposition theorem. The streamwise coordinate-dependent factor of the inner eigen-solutions, first found by M. E. Goldstein for the flat plate, is generalized for arbitrary pressure gradients.
Unsteady Flow in the Obstructed Space Between Disks Corotating in a Cylindrical Enclosure
Authors: Usry W. R. , Humphrey J. A. C. , Greif R.
Published: May 2008

Time-resolved measurements of the circumferential velocity component were obtained with a laser-Doppler velocimeter in the space between the center pair of four disks corotating in air in an axisymmetric cylindrical enclosure. The separate influences on the flow of two obstructions of similar shapes but having different lengths were investigated. The results show that both obstructions significantly alter the mean and rms distributions of velocity in quantitatively different but qualitatively similar ways. Both obstructions also alter the characteristic frequencies of flow oscillations associated with large scale motions present in the flow, apparently of the type that arise in unobstructed configurations. The measurements suggest that an obstruction can induce bimodal states of motion over frequency ranges that depend on the obstruction’s length. The presence of an obstruction increases the strength of the cross-stream secondary motion in the inter-disk space by redirecting fluid moving in the circumferential direction towards the radial direction. While this reduced the magnitude of the velocity deficit in the obstruction wake, for the cases investigated the flow did not recover within one revolution from the effects of either obstruction.
Numerical Simulations of Three-Dimensional Flows in a Cubic Cavity With an Oscillating Lid
Authors: Iwatsu Reima , Hyun Jae Min , Kuwahara Kunio
Published: May 2008

Numerical studies are made of three-dimensional flow of a viscous fluid in a cubical container. The flow is driven by the top sliding wall, which executes sinusoidal oscillations. Numerical solutions are acquired by solving the time-dependent, three-dimensional incompressible Navier-Stokes equations by employing very fine meshes. Results are presented for wide ranges of two principal physical parameters, i.e., the Reynolds number, Re ≤ 2000 and the frequency parameter of the lid oscillation, ω′ ≤ 10.0. Comprehensive details of the flow structure are analyzed. Attention is focused on the three-dimensionality of the flow field. Extensive numerical flow visualizations have been performed. These yield sequential plots of the main flows as well as the secondary flow patterns. It is found that the previous two-dimensional computational results are adequate in describing the main flow characteristics in the bulk of interior when ω′ is reasonably high. For the cases of high-Re flows, however, the three-dimensional motions exhibit additional complexities especially when ω′ is low. It is asserted that, thanks to the recent development of the supercomputers, calculation of three-dimensional, time-dependent flow problems appears to be feasible at least over limited ranges of Re.
Effect of IC Engine Operating Conditions on Combustion and Emission Characteristics
Authors: Lu Jiang , Gupta Ashwani K. , Keating Eugene L.
Published: May 2008

Numerical simulation of flow, combustion, heat release rate, and pollutants emission characteristics have been obtained using a single cylinder internal combustion engine operating with propane as the fuel. The data show that for good agreement with experimental results on the peak pressure and the rate of pressure rise as a function of crank angle, spark ignition energy and local cylinder pressure must be properly modeled. The results obtained for NO and CO showed features which are qualitatively in good agreement and are similar to those reported in the literature for the chosen combustion chamber geometry. The results have shown that both the combustion chamber geometry and engine operating parameters affects the flame growth within the combustion chamber which subsequently affects the pollutants emission levels. The code employed the time marching procedure and solves the governing partial differential equations of multicomponent chemically reacting fluid flow by finite difference method. The numerical results provide a cost effective means of developing advanced internal combustion engine chamber geometry design that provides high efficiency and low pollution levels. It is expected that increased computational tools will be used in the future for enhancing our understanding of the detailed combustion process in internal combustion engines and all other energy conversion systems. Such detailed information is critical for the development of advanced methods for energy conservation and environmental pollution control.
Flow Field in the Secondary, Seal-Containing Passages of Centrifugal Pumps
Authors: Baskharone E. A. , Hensel S. J.
Published: May 2008

This paper illustrates the impact of seal configuration on the through-flow leakage in centrifugal pumps with shrouded impellers. The flow model is based on the Petrov-Galerkin finite element method, and the computational domain permits the primary/secondary flow interaction at both ends of the clearance gap. The model is applied to a hydraulic pump with two different seal configurations for the purpose of comparison. The computed results show a strong dependency of the leakage flow percentage and swirl-velocity retention on the overall shape of the shroud-to-housing passage including, in particular, the seal geometry. The results are generally consistent with documented observations and measurements in similar pump stages. From a rotordynamic standpoint, the current computational model conceptually provides the centered-rotor “zeroth-order” flow field for existing perturbation models of fluid/rotor interaction. The flow model is applied to two different secondary passage configurations of a centrifugal pump, and the results used in interpreting existing rotordynamic data concerning the same passage configurations.
A Pressure-Velocity Solution Strategy for Compressible Flow and Its Application to Shock/Boundary-Layer Interaction Using Second-Moment Turbulence Closure
Authors: Lien F.-S. , Leschziner M. A.
Published: May 2008

A nonorthogonal, collocated finite-volume scheme, based on a pressure-correction strategy and originally devised for general-geometry incompressible turbulent recirculating flow, has been extended to compressible transonic conditions. The key elements of the extension are a solution for flux variables and the introduction of streamwise-directed density-retardation which is controlled by Mach-number-dependent monitor functions, and which is applied to all transported flow properties. Advective fluxes are approximated using the quadratic scheme QUICK or the second-order TVD scheme MUSCL, the latter applied to all transport equations, including those for turbulence properties. The procedure incorporates a number of turbulence models including a new low-Re k–ε eddy-viscosity variant and a Reynolds-stress-transport closure. The predictive capabilities of the algorithm are illustrated by reference to a number of inviscid and turbulent transonic applications, among them a normal shock in a Laval nozzle, combined oblique-shock reflection and shock-shock interaction over a bump in a channel and shock-induced boundary-layer separation over channel bumps. The last-named application was computed both with eddy-viscosity models and Reynolds-stress closure, leading to the conclusion that the latter yields a much greater sensitivity of the boundary layer to the shock and, arising therefrom, a more pronounced λ-shock structure, earlier separation and more extensive recirculation. On the other hand, the stress closure is found to return an insufficient rate of wake recovery following reattachment.
Effect of Particle Residence Time on Particle Dispersion in a Plane Mixing Layer
Authors: Ishima Tsuneaki , Hishida Koichi , Maeda Masanobu
Published: May 2008

A particle dispersion has been experimentally investigated in a two-dimensional mixing layer with a large relative velocity between particle and gas-phase in order to clarify the effect of particle residence time on particle dispersion. Spherical glass particles 42, 72, and 135 μm in diameter were loaded directly into the origin of the shear layer. Particle number density and the velocities of both particle and gas phase were measured by a laser Doppler velocimeter with modified signal processing for two-phase flow. The results confirmed that the characteristic time scale of the coherent eddy apparently became equivalent to a shorter characteristic time scale due to a less residence time. The particle dispersion coefficients were well correlated to the extended Stokes number defined as the ratio of the particle relaxation time to the substantial eddy characteristic time scale which was evaluated by taking account of the particle residence time.
Experimental Results for the Rotordynamic Characteristics of Leakage Flows in Centrifugal Pumps
Authors: Guinzburg A. , Brennen C. E. , Acosta A. J. , Caughey T. K.
Published: May 2008

In recent years, increasing attention has been given to fluid-structure interaction problems in turbomachines. The present research focuses on just one such fluid-structure interaction problem, namely, the role played by fluid forces in determining the rotordynamic stability and characteristics of a centrifugal pump. The emphasis of this study is to investigate the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. An experiment was designed to measure the rotordynamic shroud forces due to simulated leakage flows for different parameters such as flow rate, shroud clearance, face-seal clearance and eccentricity. The data demonstrate substantial rotordynamic effects and a destabilizing tangential force for small positive whirl frequency ratios; this force decreased with increasing flow rate. The rotordynamic forces appear to be inversely proportional to the clearance and change significantly with the flow rate. Two sets of data taken at different eccentricities yielded quite similar nondimensional rotordynamic forces indicating that the experiments lie within the linear regime of eccentricity.
Weak Thermal Vortex Rings
Authors: Ganapathy R.
Published: May 2008

A simple mathematical model is proposed and a similarity solution is obtained to study the behavior of very weak thermal vortex rings induced by a horizontal line source of thermal energy in an unbounded fluid. The temperature distribution is assumed to be unaffected by the fluid motion, and the Stokes flow approximation is invoked. Streamlines are computed to demonstrate the evolution of the flow field.
Comparison of the Triple-Deck Theory, Interactive Boundary Layer Method, and Navier-Stokes Computation for Marginal Separation
Authors: Hsiao Chao-Tsung , Pauley Laura L.
Published: May 2008

The steady two-dimensional marginal separation of an incompressible boundary layer flow within a channel was solved independently by three different methods: the triple-deck method of marginal separation, the interactive boundary layer method, and the full Navier-Stokes computation. From comparison of the results between these three methods, the accuracy and appropriateness of each method was determined. The critical condition beyond which the steady marginal separation solution of triple-deck method does not exist was related to a physical phenomenon in which the separation bubble becomes unsteady. Factors such as Reynolds number and pressure gradient distribution which might influence the accuracy of the marginal separation solution were also investigated.
Separated-Reattaching Flow Over a Backstep With Uniform Normal Mass Bleed (Data Bank Contribution)
Authors: Yang Jing-Tang , Tsai Bor-Bin , Tsai Go-Long
Published: May 2008

The effect of normal mass bleed into the separated-reattaching flow behind a backward-facing step has been experimentally investigated. Results of LDA measurements showed that normal mass bleed suppressed the reverse horizontal velocity, the reverse flow rate, turbulence intensity, and Reynolds shear stress within the whole recirculating zone. An analysis of the distributions of vertical velocity and turbulence intensity indicates that the interaction between the injected fluid and the main stream began at 0.4 step height and became significant after 0.8 step height behind the backstep.
Origin and Decay of Longitudinal Vortices in Developing Flow in a Curved Rectangular Duct (Data Bank Contribution)
Authors: Kim Wu J. , Patel Virendra C.
Published: May 2008

Developing turbulent flow in a 90 deg curved duct of rectangular cross-section, and an aspect ratio of 6, was investigated. Mean-velocity and Reynolds-stress components were measured using a five-hole pressure probe and two-sensor hot-wire probes, respectively, in the boundary layers on the duct walls to document the pressure-driven secondary motion and the formation of a longitudinal vortex near the corner on the convex wall. Special attention was paid to the three-dimensionality of the flow exiting the two-dimensional contraction of the wind tunnel in order to provide proper inlet boundary conditions for future computational work. The mean velocities and wall shear stresses were measured at seven sections and turbulence measurement were made at four sections. The data provide insights into the development of three-dimensional turbulent boundary layers under the influence of strong streamwise curvature, both convex or concave, and attendant pressure gradients, and clearly elucidate the mechanism by which strong pressure-driven secondary motion results in a longitudinal vortex.
The Stability of Pipe Entrance Flows Subjected to Axisymmetric Disturbances
Authors: da Silva D. F. , Moss E. A.
Published: May 2008

This paper reexamines an important unresolved problem in fluid mechanics—the discrepancy between measurements and predictions of stability in pipe entrance flows. Whereas measured critical Reynolds numbers are relatively insensitive to velocity profile shape in the streamwise direction, the theoretical results indicate a rapid increase, both as the equilibrium profile is approached, and toward the inlet. The current work uses the displacement thickness based Reynolds number as a rational basis on which to compare new stability predictions obtained by means of the Q-Z algorithm, with existing theoretical results. Although the present data are shown to be the only that are consistent with the classical parallel boundary layer limit towards the inlet, they still deviate increasingly with axial distance from the only available experimental results. By examining pipe inlet stability data in relation to boundary layer measurements and predictions, the work effectively questions the commonly held belief that streamwise variations of flow alone are responsible for these deviations, suggesting that the finite amplitude nature of the applied disturbances is the most likely cause.
Perspective: Future Research Directions in Computational Fluid Dynamics
Authors: Douglass R. W. , Ramshaw J. D.
Published: May 2008

The current state of computational fluid dynamics (CFD) has yet to reach its full promise as a general tool for engineering design and simulation. Research in the areas of code robustness, complex flows of real fluids, and numerical errors and resolution are proposed as directions aiming toward that goal. We illustrate some of the current CFD challenges using selected applications.
The Effect of Sensor Size on the Performance of Flush-Mounted Hot-Film Sensors
Authors: Moen M. J. , Schneider S. P.
Published: May 2008

A parametric study was performed to determine the effect of sensor size on the performance of flush-mounted hot-film sensors, operated using constant-temperature anemometry. Three nickel sensors with surfaces of 12.5 × 125 microns, 25 × 250 microns, and 50 × 500 microns were deposited on glass flat-plate substrates. The frequency response and sensitivity of the sensors were measured using both electrical and flow testing. Electrical testing was performed using both sine and square waves. Flow testing was performed in a shock tube by subjecting the flush-mounted sensors to a shock-induced boundary layer. As the sensor size was decreased, frequency response increased and sensitivity decreased. These trends were observed for both electronic and flow testing conditions.
Power Augmentation Effects of a Horizontal Axis Wind Turbine With a Tip Vane—Part 1: Turbine Performance and Tip Vane Configuration
Authors: Shimizu Yukimaru , Yoshikawa Takaya , Matsumura Shinji
Published: May 2008

This paper describes the experimental results of output power augmentation of a horizontal axis wind turbine with a tip vane. In order to find the relationship between the performance of the turbine and the configuration of the tip vane, various types and sizes were used. It was found that V-type and S-type tip vanes can improve turbine performance. Also, the dimensions of V- and S-type tip vanes were investigated. The maximum improvement achieved was a 25 percent increase in power in an existing wind turbine without a tip vane.
Power Augmentation Effects of a Horizontal Axis Wind Turbine With a Tip Vane—Part 2: Flow Visualization
Authors: Shimizu Yukimaru , Yoshikawa Takaya , Matsumura Shinji
Published: May 2008

This paper presents a discussion of the physics of the flow discussed in our first report (Shimizu, Y. et al., 1990). By visualizing the flow around the tip vane, the following results were drawn: 1) The strength of the tip vortex, the induced drag and turbulence on the blade tip can be diminished with a tip vane. 2) The inflow rate to the rotary surface of wind turbine can be increased with the tip vane.
Analytical Solutions for Flow of a Dusty Fluid Between Two Porous Flat Plates
Authors: Chamkha Ali J.
Published: May 2008

Equations governing flow of a dusty fluid between two porous flat plates with suction and injection are developed and closed-form solutions for the velocity profiles, displacement thicknesses, and skin friction coefficients for both phases are obtained. Graphical results of the exact solutions are presented and discussed.
Characteristics of Swirling Flow in a Circular Pipe
Authors: Li Hui , Tomita Yuji
Published: May 2008

This paper examines experimentally the decay of swirl, the average dynamic, static and total pressures and the wall pressure in a pipeline 13 m in length and with an inside diameter of 80 mm for two Reynolds numbers and five different inlet swirls. The empirical correlations for the above quantities are derived, and by using these empirical correlations, the decay process and pressure distributions along the pipe for the swirling flow can be successfully computed by giving discharge velocity and a wall static pressure at any axial position.
A Note on Irrotational Curvilinear Flow Past a Weir
Authors: Ramamurthy Amruthur S. , Vo Ngoc-Diep , Balachandar R.
Published: May 2008

Curvilinear flows are commonly encountered in hydraulic engineering practice. Detailed velocity surveys of the curvilinear flow field over a circular-crested two dimensional weir were obtained using laser doppler velocimetry (LDV). Using these test data, the basic assumptions related to the streamline geometry and irrotational of flow over weirs made in all existing theoretical weir models are verified. The test data yielded the pattern, slope and curvature of the streamlines. Water surface profiles were also obtained to determine the depth of flow over the crest and the radius of curvature of the surface streamline at the crest section. As part of the study, the velocity profile of the flow over the weir crest was integrated to obtain the weir discharge coefficient. The weir coefficient obtained on the basis of this empirical procedure is compared with the weir coefficient based on direct discharge measurement.
Wall Pressure and Shear Stress Variations in a 90-Deg Bifurcation During Pulsatile Laminar Flow
Authors: Khodadadi J. M.
Published: May 2008

Wall pressure distribution and shear stress fields for pulsatile laminar flow in a 90-degree bifurcation with rectangular cross sections are evaluated using the results of the numerical solution of the Navier-Stokes equation. The extent of the adverse pressure gradient on the bottom wall of the main duct and the upstream wall of the branch closely correlate to the behavior of the two dynamic recirculation zones which are formed on these two walls. Multiple zones of high and low shear stresses at various sites in the bifurcation are observed. The extent of the fluctuations of the maximum and minimum shear stress is identified. Next-to-the-wall laser Doppler anemometer velocity measurements are used to estimate the shear stress distribution on the walls. In general, qualitative agreement between the experimental and computed wall shear stress values is observed. The variation of the wall shear stress in the vicinity of the branch is discussed in light of the highly perturbed flow field.
Effect of Crossflow on Oscillatory Flow in a Porous Medium Between Two Parallel Plates in Relative Motion
Authors: Kumaran V. , Ramanaiah G.
Published: May 2008

This paper deals with the incompressible flow through a porous medium bounded by two parallel permeable plates, one of which is stationary and the other slides and oscillates in its own plane. Also uniform crossflow is superimposed through the plates. Analytical solutions for flow parameters are obtained. The effect of crossflow, permeability, and the frequency of the moving plate on the velocity, skin friction has been investigated. It is shown that skin friction can be reduced considerably by injection at the lower plate.
Turbulent Flow Around a Bluff Rectangular Plate. Part I: Experimental Investigation
Authors: Djilali N. , Gartshore I. S.
Published: May 2008

Measurements are reported for the separted reattaching flow around a long rectangular plate placed at zero incidence in a low-turbulence stream. This laboratory configuration, chosen for its geometric simplicity, exhibits all of the important features of two-dimensional flow separation with reattachment. Conventional hot-wire anemometry, pulsed-wire anemometry and pulsed-wire surface shear stress probes were used to measure the mean and fluctuating flow field at a Reynolds number, based on plate thickness, of 5 × 104. The separated shear layer appears to behave like a conventional mixing layer over the first half of the separation bubble, where it exhibits an approximately constant growth rate and a linear variation of characteristic frequencies and integral timescales. The characteristics of the shear layer in the second half of the bubble are radically altered by the unsteady reattachment process. Much higher turbulent intensities and lower growth rates are encountered there, and, in agreement with other reattaching flow studies, a low frequency motion can be detected.
Effect of Suction on the Stability of Supersonic Boundary Layers. Part I—Second-Mode Waves
Authors: Al-Maaitah A. A. , Nayfeh A. H. , Masad J. A.
Published: May 2008

The effect of suction on the second (Mack) mode of instability in supersonic and hypersonic two-dimensional boundary layers is investigated. The results show that suction has a stabilizing effect on these waves; it reduces the peak amplification and shifts it toward a higher frequency. In the presence of suction, the most amplified Mack mode remains two-dimensional. The effectiveness of suction in stabilizing Mack waves decreases as the Mach number increases. Variations of the growth rates of the most amplified Mack mode and the corresponding frequencies and wave numbers with mass flux are found to be almost linear. The frequencies and wave numbers corresponding to the most amplified Mack mode increase by increasing the suction level.
Air Test Flow Analysis of the Hydrogen Pump of Vulcain Rocket Engine
Authors: Bario F. , Barral L. , Bois G.
Published: May 2008

Within the framework of the technological development of the VULCAIN rocket engine (Ariane V European project), initiated by the Centre National d’Etudes Spatiales (CNES) for the Agence Spatiale Europe´enne (ESA), the Socie´te´ Europe´enne de Propulsion (SEP) is in charge of the design and building of the liquid hydrogen turbopump. In order to characterize the hydraulic performance of the pump, an air test facility reproducing the pump geometry was built by SEP and fitted in the Laboratoire de Me´canique des Fluides et d’Acoustique of the Ecole Centrale de Lyon. Benefits and disadvantages of air tests of hydraulic pumps are discussed. The pump is composed of three stages. The first one is an axial inducer stage. The second and third ones are centrifugal stages with vaned diffusers and are separated by a U bend and a vaned return channel. Results of the first measurement campaign are presented. They consist of overall pressure, wall static pressure and velocity measurements. Local quantities (velocity triangle, pressure) and mean quantities (pressure rise, losses, efficiency) are given. Recirculating and wake flow analysis are included. The goals of the study are the understanding of the flow behavior and the improvement of the prediction methods. Predicted and measured quantities (losses, efficiency, kinetic momentum) are compared. The hydrogen performances are deduced, they agree with the specified performances of the pump. This validation is one of the main results achieved.
Flow Measurements in a Model Burner—Part 1
Authors: Dura˜o D. F. G. , Heitor M. V. , Moreira A. L. N.
Published: May 2008

Laser-Doppler measurements of mean and turbulent velocity characteristics are reported in the developing region of the isothermal flow of a model of an industrial oxy-fuel burner. The burner consists of a central axisymmetric jet surrounded by sixteen circular jets, simulating the injection of oxygen in pratical burners. Errors incurred in the laser-Doppler measurements are estimated and bias effects due to unequal number density of seed particles in the various jet flows are investigated. The experiments have been carried out to investigate the mixing efficiency of the burner assembly without swirl motion and to assess the accuracy of calculation procedures in industrial burners. The results show that the present flow develops faster than related coaxial free jets with the same velocity ratio between central and peripheral air streams due to the comparatively high mixing rate peculiar to the present configuration. The existence of zones characterized by large turbulence anisotropy indicates the need to take account of the normal stresses in any proposed mathematical model to simulate the present flow field.
MeCP2, a Key Contributor to Neurological Disease, Activates and Represses Transcription
Authors: Chahrour Maria , Jung Sung Yun , Shaw Chad , Zhou Xiaobo , Wong Stephen T. C. , Qin Jun , Zoghbi Huda Y.
Published: May 2008

Mutations in the gene encoding the transcriptional repressor methyl-CpG binding protein 2 (MeCP2) cause the neurodevelopmental disorder Rett syndrome. Loss of function as well as increased dosage of theMECP2gene cause a host of neuropsychiatric disorders. To explore the molecular mechanism(s) underlying these disorders, we examined gene expression patterns in the hypothalamus of mice that either lack or overexpress MeCP2. In both models, MeCP2 dysfunction induced changes in the expression levels of thousands of genes, but unexpectedly the majority of genes (∼85%) appeared to be activated by MeCP2. We selected six genes and confirmed that MeCP2 binds to their promoters. Furthermore, we showed that MeCP2 associates with the transcriptional activator CREB1 at the promoter of an activated target but not a repressed target. These studies suggest that MeCP2 regulates the expression of a wide range of genes in the hypothalamus and that it can function as both an activator and a repressor of transcription.
Comment on "Mixed-Layer Deepening During Heinrich Events: A Multi-Planktonic Foraminiferal δ
18
O Approach"
Authors: Hillaire-Marcel Claude , de Vernal Anne
Published: May 2008

Rashid and Boyle (Reports, 19 October 2007, p. 439) analyzed oxygen isotopes in planktonic foraminera from marine sediments and concluded that Heinrich events (massive iceberg discharges into the North Atlantic Ocean) caused upper water masses to deepen. We question the robustness of this interpretation and argue that a strongly stratified mixed layer characterized by dense sea-ice cover and production of oxygen-18–depleted brines likely prevailed during such events.
Sharing Data, Constructing Science
Authors: Hahn Karla L.
Published: May 2008

Scholarship in the Digital Age
. Information, Infrastructure, and the Internet.
By Christine L. Borgman
. MIT Press, Cambridge, MA, 2007. 360 pp. $35, £22.95. ISBN 9780262026192.

The author's consideration of the practices and issues affecting scholarly communication highlights the social and political environments rather than the technological aspects of information dissemination.
Log or Linear? Distinct Intuitions of the Number Scale in Western and Amazonian Indigene Cultures
Authors: Dehaene Stanislas , Izard Véronique , Spelke Elizabeth , Pica Pierre
Published: May 2008

The mapping of numbers onto space is fundamental to measurement and to mathematics. Is this mapping a cultural invention or a universal intuition shared by all humans regardless of culture and education? We probed number-space mappings in the Mundurucu, an Amazonian indigene group with a reduced numerical lexicon and little or no formal education. At all ages, the Mundurucu mapped symbolic and nonsymbolic numbers onto a logarithmic scale, whereas Western adults used linear mapping with small or symbolic numbers and logarithmic mapping when numbers were presented nonsymbolically under conditions that discouraged counting. This indicates that the mapping of numbers onto space is a universal intuition and that this initial intuition of number is logarithmic. The concept of a linear number line appears to be a cultural invention that fails to develop in the absence of formal education.
Paper Museums
Authors: Ash Caroline
Published: May 2008

Amazing Rare Things
. The Art of Natural History in the Age of Discovery.
Royal Collection Curators
. The Queen's Gallery, Buckingham Palace, London. Through 28 September 2008.
www.royalcollection.org.uk/microsites/amazingrarethings/

Amazing Rare Things
. The Art of Natural History in the Age of Discovery.
By David Attenborough, Susan Owens, Martin Clayton, and Rea Alexandratos
. Royal Collection, London, 2007. 223 pp. £18.95. ISBN 9781902163468. Paper, £9.95. ISBN 9781902163994. Yale University Press, New Haven, CT, 2007. 223 pp. $37.50. ISBN 9780300125474.

This small exhibition highlights natural history drawings and paintings by Leonardo da Vinci, Alexander Marshal, Maria Sibylla Merian, and Mark Catesby and the paper museum of Cassiano dal Pozzo.
Mycobacterium haemophilum
Epididymal Abscess in a Renal Transplant Patient
Authors: Keller Marina , Mak Anton , Thibert Louise , Rene Pierre , Klein Marina B.
Published: May 2008

Mycobacterium haemophilum
is an established cause of cutaneous lesions in immunocompromised hosts. We report the first known case of epididymal abscess, which highlights the need to work up all specimens that are acid-fast bacillus-positive for
M. haemophilum
from immunocompromised hosts, regardless of body site.
Application of a Novel, Rapid, and Sensitive Oligonucleotide Ligation Assay for Detection of Cancer-Predicting Mutations in the Precore and Basal Core Promoter of Hepatitis B Virus
Authors: Mendy M. E. , Kaye S. , Le Roux E. , Kirk G. D. , Jeng-Barry A. , McConkey S. , Cotten M. , Kuniholm M. H. , Leligdowicz A. , Hainaut P. , Rowland-Jones S. , Whittle H.
Published: May 2008

Hepatocellular carcinoma (HCC) and cirrhosis are important causes of mortality worldwide. Persistent hepatitis B virus (HBV) infection is a major cause of these diseases. Double mutations in the basal core promoter (BCP) (A1762T and G1764A) and precore (pre-C) (G1896A) regions of the virus are associated with progression to HCC. The current study is aimed at developing a simple method for screening and detecting BCP and pre-C mutations in HBV carriers. We have developed and validated an oligonucleotide ligation assay (OLA) to detect point mutations in the HBV core gene. We have applied OLA methods to samples from HBV-infected carriers recruited from the Gambia Liver Cancer Study (GLCS) comprising asymptomatic HBsAg carriers, patients with cirrhosis, and patients with HCC. We observed an 89.3% and 95.8% concordance between the OLA and DNA sequencing for BCP and pre-C mutations, respectively. OLA detected the mutations in single-strain infections and in infections with mixtures of wild-type and mutant viruses under conditions where sequencing detected only the single dominant strains. BCP mutations were detected in 75.7% of patients with advanced liver disease (cirrhosis/HCC) compared to 47.6% of asymptomatic carriers, while pre-C mutations were detected in 34.5% of advanced liver disease patients and in 47.6% of asymptomatic HBsAg carriers. There was a significant association between the presence of BCP mutations and advanced liver disease. In conclusion, OLA is a simple, economical, and reliable assay for detection of pre-C and BCP mutations. Its application can lead to improvement in diagnosis and clinical care in regions where HBV is endemic.
Reactive-Site Cleavage Residues Confer Target Specificity to Baculovirus P49, a Dimeric Member of the P35 Family of Caspase Inhibitors
Authors: Guy Michael P. , Friesen Paul D.
Published: May 2008

Baculovirus proteins P49 and P35 are potent suppressors of apoptosis in diverse organisms. Although related, P49 and P35 inhibit initiator and effector caspases, respectively, during infection of permissive insect cells. The molecular basis of this novel caspase specificity is unknown. To advance strategies for selective inhibition of the cell death caspases, we investigated biochemical differences between these baculovirus substrate inhibitors. We report here that P49 and P35 use similar mechanisms for stoichiometric inhibition that require caspase cleavage of their reactive site loops (RSL) and chemical contributions of a conserved N-terminal cysteine to stabilize the resulting inhibitory complex. Our data indicated that P49 functions as a homodimer that simultaneously binds two caspases. In contrast, P35 is a monomeric, monovalent inhibitor. P49 and P35 also differ in their RSL caspase recognition sequences. We tested the role of the P
4
-P
1
recognition motif for caspase specificity by monitoring virus-induced proteolytic processing of Sf-caspase-1, the principal effector caspase of the host insect
Spodoptera frugiperda
. When P49's TVTD recognition motif was replaced with P35's DQMD motif, P49 was impaired for inhibition of the initiator caspase that cleaves and activates pro-Sf-caspase-1 and instead formed a stable inhibitory complex with active Sf-caspase-1. In contrast, the effector caspase specificity of P35 was unaltered when P35's DQMD motif was replaced with TVTD. We concluded that the TVTD recognition motif is required but not sufficient for initiator caspase inhibition by P49. Our findings demonstrate a critical role for the P
4
-P
1
recognition site in caspase specificity by P49 and P35 and indicate that additional determinants are involved in target selection.