bluuebunny/crossref_metadata_2025 huggingface dataset:
Average Physical Parameters in an Air-Water Two-Phase Flow in a Small, Square-Sectioned Channel
Authors: Keska J. K. , Fernando R. D.
Published: May 2008

This experimental study focuses on an adiabatic two-phase air-water flow generated in a small, horizontal, 6.35 mm square channel. Pressure and temperature were near standard conditions. Experimental data and correlations available in the literature, generally, do not consider the full range of concentration, small cross-sectional areas and direct physical parameters, such as concentration (void fraction) and/or phase velocities. Based on the direct measurement of in-situ spatial concentration (in a full range of concentrations, including gas and liquid phases only), and flow-pattern determination, the experimental data from the study are compared with data from the literature and with prediction by the generally accepted Lockhart-Martinelli’s and Chen’s models. Spatial concentration measurements were made with a computer-based system developed and built by the authors. Pressure drop over a length of the channel was also measured with pressure transducers. These measurements were made for a variety of flow conditions which encompassed bubble, slug, plug, and annular flow regimes. Flow patterns were established, and both mean and fluctuating components of the concentration measurements were used to objectively identify the flow patterns. These results, together with visual enhanced observation (stroboscope) supplemented with a high-speed CCD camera recording enhanced with dye injection, were used to obtain flow-pattern maps and compared with the literature. Spatial concentration is shown to be a key physical parameter in describing the state of the mixture in two-phase flow.
LDV Measurements in Separated Flow on an Elliptic Wing Mounted at an Angle of Attack on a Wall
Authors: Parthasarathy R. N. , Sirviente A. I. , Patel V. C.
Published: May 2008

The flow around a half-ellipsoid with axes ratio 12:6:1 mounted on a plane wall at an angle of attack of 25° and at a Reynolds number of 47,000 (based on the maximum chord) was studied using a three-dimensional LDV system. In this paper the mean velocity distributions in a volume enclosing the separated region and the near wake are described. The flow is shown to be consistent with the findings of Johnson (1991) based on flow visualization and related topological analysis. The flow on most of the pressure side was attached and laminar, while that on the suction side and in the wake was separated and turbulent. The region of separation had mean negative streamwise velocities as large as 25 percent of the freestream velocity, and the reversed-flow region extended up to one chord length behind the body. The measurements clearly reveal the complex vortex structure that arises from the three-dimensional separation.
Particle Tracking Velocimetry Using Laser-Beam Scanning and Its Application to Transient Flows Driven by a Rotating Disk
Authors: Ushijima S. , Tanaka N.
Published: May 2008

A particle tracking velocimetry (PTV) system has been developed to obtain instantaneous two velocity components on several sections in three-dimensional space. The flow visualization is conducted by means of parallel laser-light sheets created by a scanning laser beam and the visualized particle images are taken by a highspeed video system synchronized with the scanning. In order to obtain higher accuracy in velocity measurements than usual PTV, some improvements are made on the analyzing procedures: the extraction of particle images, the determination of their center points, the derivation of velocity components and others. The present PTV was applied to the transient flows in a cylindrical tank with a rotating disk. As a result, two-dimensional transient flow patterns with large scale disturbances are continuously captured in three-dimensional space.
Ship’s Propulsion Mechanism of Two-Stage “Weis-Fogh” Type
Authors: Tsutahara Michihisa , Kimura Takeyoshi , Ro Kideok
Published: May 2008

The dynamic properties of a ship’s two-stage “Weis-Fogh” type propulsion mechanism are experimentally and numerically investigated. In order to study the effects of the interaction of the two wings, the wings are designed in a manner that enable them to move close to each other. The opening angle and the moving speed are the same for both wings. Two cases of the phase differences of the wings’ motions are considered, the in-phase case and the out-of-phase case. The differences of the dynamic properties between the two wings are shown and the properties of this propulsion mechanism are discussed.
Electromagnetic Pump With Thin Metal Walls
Authors: Ma N. , Moon T. J. , Walker J. S.
Published: May 2008

This paper treats a liquid-metal flow in a rectangular duct with a strong, uniform, transverse magnetic field and with thin metal walls, except for two finite-length, perfectly conducting electrodes in the side walls, which are parallel to the magnetic field. There are large velocities inside the boundary layers adjacent to the thin metal side walls, but not inside the layers adjacent to the electrodes. Upstream and downstream of the electrodes, a significant fraction of the total flow leaves and enters the side-wall boundary layers, respectively. For the particular duct treated here, the fully developed side layers, which carry 38.8 percent of the total flow, are realized at a distance of three characteristic lengths from the ends of the electrodes.
Flow Characteristics of a Centrifugal Pump
Authors: Liu C. H. , Vafidis C. , Whitelaw J. H.
Published: May 2008

Measurements of velocity have been obtained in a centrifugal pump in terms of angle-resolved values in the impeller passages, the volute, the inlet and exit ducts and are presented in absolute and relative frames. The pump comprised a radial flow impeller with four backswept blades and a single volute, and the working liquid had the same refractive index as the transparent casing to facilitate the use of a laser-Doppler velocimeter. The flows in the impeller passages were found to depart from the curvature of the blade surfaces at off-design conditions with separation from the suction surface and from the shroud. Secondary flows from the suction to pressure surfaces were dominated by the influences of the relative motion between the shroud and impeller surfaces and the tip leakage. Geometric differences of 0.5 mm and one degree in spacing of the four blades caused differences in passage velocity of up to 6 percent of the impeller tip velocity close to the design flowrate and up to 16 percent at the lowest discharge. The flowrate from each impeller passage varied with volute circumferential position by up to 25 percent at an off-design flowrate. Poor matching of the impeller and volute at off-design conditions caused swirl and separation in the inlet and exit pipes.
Preliminary Design of Centrifugal Impellers Using Optimization Techniques
Authors: AL-Zubaidy Sarim
Published: May 2008

The paper proposes a design method which may be used to evaluate the detailed geometry of an impeller (handling compressible and perfect fluid) from a prescribed mean streamline velocity distribution. The analysis makes use of numerical optimization, firstly in the step by step channel geometry calculation, and secondly in controlling the manner in which the relative velocity components are permitted to vary along the mean streamline for the condition of minimum entropy generation along the flow path. The components distribution of the relative velocity were not allowed to take arbitrary values, the variation of the radial, axial and tangential components was governed in such a way that the prescribed diffusion schedule is satisfied at every calculation point. The general configuration of the example design shows it to be well proportional and should not be difficult to manufacture.
Two-Phase Velocity Distributions and Overall Performance of a Centrifugal Slurry Pump
Authors: Cader T. , Masbernat O. , Roco M. C.
Published: May 2008

Back-scattering LDV has been used to investigate particulate two-phase flow in a centrifugal slurry pump. The measurements reported here have been made with a dilute suspension of 0.8 mm glass beads at the impeller-casing flow interface. This interface is of practical importance because the corresponding velocity and concentration results can be used to determine the pump head and flowrate. The present study evaluates the connection between the liquid and solids velocity distribution measured around the impeller and the pump performance determined from measurements at the pump inlet and outlet. The analysis of the velocity triangles for both phases shows the effect of the pump flowrate and inlet recirculation on the pump head at the impeller outlet, as well as the effect of particle slip on pump energy efficiency. A separate group of characteristic curves is proposed to represent the periodical fluctuations of the pump flowrate, head, and loss of efficiency due to particle slip, as a function of the impeller position.
Hydrodynamic Design Considerations for Hydroacoustic Facilities: Part I—Flow Quality
Authors: Wetzel J. M. , Arndt R. E. A.
Published: May 2008

Design studies are described for two recently completed large scale hydroacoustic test facilities (one of which is the world’s largest). These recirculating water tunnels have a different configuration than conventional tunnels, and special hydrodynamic design studies were required to evaluate and optimize the performance of some critical components. This paper considers the flow quality in the test section as influenced by the design of the contraction and the turbulence management system. Numerical modeling and experimental work were used to arrive at an acceptable nonsymmetrical nozzle design. Studies were also made of a turbulence management system using honeycombs rather than screens as typically used. Although design goals for turbulence levels were met, this study indicated that additional research in the area of turbulence management is necessary before there is a complete understanding of the overall process of turbulence attenuation.
Hydrodynamic Design Considerations for Hydroacoustic Facilities: Part II—Pump Design Factors
Authors: Wetzel J. M. , Arndt R. E. A.
Published: May 2008

The St. Anthony Falls Hydraulic Laboratory has been involved in the hydrodynamic design of large cavitation facilities, which require a high performance axial flow pump that is cavitation free to meet stringent design conditions. As cavitation has been shown to be the largest noise source in an otherwise well designed facility, it must be eliminated for the design range of flow conditions. To reduce the possibility of blade cavitation it is desirable to have a near uniform, or at least, a near symmetrical approach velocity distribution at the pump inlet. The design of flow facilities to achieve such an inflow was the subject of extensive investigations. These investigations consisted of both numerical and physical modeling of critical components in the test loop. The influence of these components, which included the contraction, diffuser, and turning vanes was carefully documented. The combination of the two modeling techniques will be demonstrated as an effective design tool for a high performance, hydrodynamic test facility.
Splattering During Turbulent Liquid Jet Impingement on Solid Targets
Authors: Bhunia Sourav K. , Lienhard John H.
Published: May 2008

In turbulent liquid jet impingement, a spray of droplets often breaks off of the liquid layer formed on the target. This splattering of liquid alters the efficiencies of jet impingement heat transfer processes and chemical containment safety devices, and leads to problems of aerosol formation in jet impingement cleaning processes. In this paper, we present a more complete study of splattering and improved correlations that extend and supersede our previous reports on this topic. We report experimental results on the amount of splattering for jets of water, isopropanol-water solutions, and soap-water mixtures. Jets were produced by straight tube nozzles of diameter 0.8–5.8 mm, with fully developed turbulent pipe-flow upstream of the nozzle exit. These experiments cover Weber numbers between 130-31,000, Reynolds numbers between 2700-98,000, and nozzle-to-target separations of 0.2 ≤ l/d ≤ 125. Splattering of up to 75 percent of the incoming jet liquid is observed. The results show that only the Weber number and l/d affect the fraction of jet liquid splattered. The presence of surfactants does not alter the splattering. A new correlation for the onset condition for splattering is given. In addition, we establish the range of applicability of the model of Lienhard et al. (1992) and we provide a more accurate set of coefficients for their correlation.
High Speed Liquid Impact Onto Wetted Solid Surfaces
Authors: Shi H. H. , Field J. E. , Pickles C. S. J.
Published: May 2008

The mechanics of impact by a high-speed liquid jet onto a solid surface covered by a liquid layer is described. After the liquid jet contacts the liquid layer, a shock wave is generated, which moves toward the solid surface. The shock wave is followed by the liquid jet penetrating through the layer. The influence of the liquid layer on the side jetting and stress waves is studied. Damage sites on soda-lime glass, PMMA (polymethylmethacrylate) and aluminium show the role of shear failure and cracking and provide evidence for analyzing the impact pressure on the wetted solids and the spatial pressure distribution. The liquid layer reduces the high edge impact pressures, which occur on dry targets. On wetted targets, the pressure is distributed more uniformly. Despite the cushioning effect of liquid layers, in some cases, a liquid can enhance material damage during impact due to penetration and stressing of surface cracks.
Droplet Dynamics Near the Wall in a Vertical Rectangular Duct
Authors: Wang M. R. , Huang D. Y. , Liu Y. C.
Published: May 2008

Measurements of the droplet behavior near the wall in a vertical rectangular duct were conducted by a phase Doppler particle analyzer (PDPA). The test Reynolds number and drop size range is from 18,500 to 89,300 and from 5 μm to 110 μm, respectively. Results show that the negative slip-velocity of the drops near the free-stream region normally results in the reversed slip-velocity phenomenon in the boundary layer region. No negative slip-velocity of all drops are discovered for Reynolds number less than 38,300. This indicates no reversed slip-velocity phenomenon for the test drop size range under low Reynolds number conditions. However, when the Reynolds number is over 38,300, the free-stream slip-velocity of the bigger drops becomes negative. It is found that the negative slip-velocity and, hence, the reversed slip-velocity phenomenon may take place for drop size larger than 52 μm to 90 μm depending on the flow Reynolds number.
Droplet Sizing Using the Shifrin Inversion
Authors: Albert R. , Farrell P. V.
Published: May 2008

A method for measuring droplet size distributions was investigated with an emphasis on limitations related to measurements in real spray environments. The method stores a photographic image of a plane of droplets within a spray and is capable of evaluating particle size distributions within the spray, one small region at a time. The method complements droplet velocity measurements made using Particle Image Velocimetry. In a typical experiment, a plane of the spray was illuminated by a laser light sheet and photographed. After processing, a small laser beam scanned the film and a diffraction pattern was generated for each region illuminated by the small laser. The diffraction pattern was inverted using a Shifrin inversion to solve for the particle size distribution within the illuminated region. In this paper we will discuss some of the limitations of this method and indicate one approach which seems to allow for improved inversions using data signal processing.
Simulation of the Turbulent Flow Inside the Combustion Chamber of a Reciprocating Engine With a Finite Element Method
Authors: Mao Y. , Buffat M. , Jeandel D.
Published: May 2008

This paper presents numerical simulations of turbulent flows during the intake and the compression strokes of a model engine. The Favre average Navier-Stokes equations are solved with a k-ε turbulence model. The numerical procedure uses a time dependent semi-implicit scheme and a finite element method with a moving mesh (Buffat, 1991, Mao, 1990). Results of 2-D axisymmetrical calculations with and without inlet swirl are presented and compared to experimental data (Lance et al., 1991). The influence of different turbulence models and the numerical precision of the simulations are also discussed.
Mean Separation and Reattachment in Turbulent Pipe Flow Due to an Orifice Plate
Authors: Agarwal N. K.
Published: May 2008

The mean flow in a pipe with turbulent separated flow due to an orifice plate is experimentally studied. Measurements of time-mean length of separation and reattachment regions, made using a surface fence gauge are presented for a range of orifice sizes. In a limited range of Reynolds number (based on orifice radial height) 3 × 104 to 7.3 × 104 studied, reattachment point location decreased from 12 to 9 step heights. The lengths of separation and reattachment regions are a function of orifice size and the Reynolds number based on the radial height of the orifice plate.
Finite-Element Analysis of Turbulent Flow in Annular Exhaust Diffusers of Gas Turbine Engines
Authors: Baskharone E. A.
Published: May 2008

A finite-element model of the turbulent flow field in the annular exhaust diffuser of a gas turbine engine is developed. The analysis is based on a modified version of the Petrov-Galerkin weighted residual method, coupled with a highly accurate biquadratic finite element of the Lagrangian type. The elemental weight functions in the finite-element formulation are so defined to ensure upwinding of the convection terms in the flow-governing equations while reverting to the conventional Galerkin’s definition for all other terms. This approach is equivalent to altering the integration algorithm as the convection terms in the element equations are derived, with the exception that the latter technique is tailored for low-order elements of the linear and bilinear types. Numerical results of the current analysis indicate that spurious pressure modes associated with this type of inertia-dominated flow are alleviated while the false numerical diffusion in the finite-element equations is simultaneously minimized. Turbulence of the flow field is modeled using the two-layer algebraic turbulence closure of Baldwin and Lomax, and the eddy viscosity calculations are performed at variably spaced points which are different from those in the finite-element discretization model. This enhances the accuracy in computing the wall shear stress and the inner/outer layer interface location. The computational model is verified using a set of experimental data at design and off-design operation modes of the exhaust diffuser in a commercial gas turbine engine. Assessment of the results in this case is favorable and, as such, provides evidence of the model capability as an accurate predictive tool in the diffuser detailed design phase.
Basic Experiments Related to the Advanced Solar Pond (ASP) Performance
Authors: Keren Y. , Bemporad G. A. , Rubin H.
Published: May 2008

This paper concerns an experimental evaluation of the basic aspects of operation of the advanced solar pond (ASP). Experiments were carried out in a laboratory test section in order to assess the feasibility of the density gradient maintenance in stratified flowing layers. The density stratification was caused by a non uniform distribution of temperatures in the flow field. Results of the experiments are reported and analyzed in the paper. Experimental data were used in order to calibrate the numerical model able to simulate heat and momentum transfer in the ASP. The numerical results confirmed the validity of the numerical model adopted, and proved the latter applicability for the simulation of the ASP performance.
Correlating Single Phase Flow Measurements With Observations of Trailing Vortex Cavitation
Authors: Green S. I.
Published: May 2008

The single phase and cavitating tip vortex shed by a NACA 66-209 rectangular plan-form, rounded tip hydrofoil has been studied. Single-phase measurements of instantaneous flow velocity were made by taking double-pulsed holograms of microbubbles moving in and around the vortex core. The tailored air bubble technique of Ooi and Acosta (1983) was employed to measure both the mean and fluctuating single phase vortex core static pressure. Cavitation inception was determined visually. The flow in the vortex core is highly unsteady; the r.m.s. axial velocity fluctuation can be as high as 0.2U∞. Core pressure fluctuations greater than the freestream dynamic pressure have been observed. These fluctuations are commensurate with the axial velocity unsteadiness. Cavitation inception in saturated water occurs at mean core pressures above the vapor pressure. However, the pressure fluctuations are certainly substantial enough to account for these elevated inception indices. The rapid establishment of fully developed trailing vortex cavitation when the cavitation number is reduced below inception is attributable to the small variation in mean core pressure with downstream distance. The inception index increases substantially with dissolved air content. The cause of this dependence is not presently known.
Application of Lumley’s Drag Reduction Model to Two-Phase Gas-Particle Flow in a Pipe
Authors: Han Kee Soo , Chung Myung Kyoon , Sung Hyung Jin
Published: May 2008

A “two-fluid model” has been incorporated with Lumley’s drag reduction model to analyze the mechanism of momentum transfer in the turbulent dilute gas-particle flow in a vertical pipe. The change of the effective viscous sublayer thickness by the presence of particles is modeled by Lumley’s theoretical model. The numerical computations of the friction factor and the pressure drop in a fully developed pipe flow are in good agreement with the corresponding experimental data for an average particle size of 15 μm. It is proved that Lumley’s model is successful in predicting the correct reduction behavior of the drag in the gas-particle flows. It has been confirmed that the effective viscous sublayer thickness for two-phase gas-particle flow is dependent on the particle relaxation time, Kolmogoroff time scale and the solids-gas loading ratio.
A Singular Perturbation Solution for Couette Flow Over a Semi-Infinite Porous Bed
Authors: Hsu C. T. , Cheng P.
Published: May 2008

An analysis has been performed to study conjugate Couette flows in a channel over a packed-spheres bed of semi-infinite extent. The Brinkman model is used as the momentum equation in the porous bed with the variation of porosity approximated by an exponential function. An approximate expression for the permeability of the bed, applicable for a wide range of porosity, is constructed. A singular perturbation solution is obtained for the velocity distribution in the packed-spheres bed. The streamwise velocity and the shearing stress of the conjugate flows in the channel and in the packed-spheres bed are matched at the fluid/porous bed interface. An explicit analytical expression for the slip coefficient is obtained by comparing the results based on the present formulation with those based on Beavers and Joseph’s formulation. It is shown that the value of the slip coefficient decreases as a result of the variable porosity effect.
The Role of Residual Nonturbulent Disturbances on Transition Onset in Two-Dimensional Boundary Layers
Authors: Govindarajan Rama , Narasimha R.
Published: May 2008

An analysis of procedures in current use for prediction of transition onset location shows that they are generally in poor agreement with data obtained in test facilities at low freestream turbulence levels. It has been shown elsewhere that under such conditions transition is driven by residual nonturbulent disturbances in the facility. A method is developed for taking such disturbances into account by defining an equivalent free-stream turbulence intensity; values for this parameter are derived for each facility from which onset data are available. A new correlation incorporating this effect is shown to be in good agreement with all available data on two-dimensional flows with pressure gradient. The correlation suggests that the onset Reynolds number (based on boundary-layer thickness) depends inversely on the total disturbance level when the latter is low.
An Erosion Resistant Pipe Bend
Authors: Horii K. , Matsumae Y. , Cheng X. M. , Takei M. , Yasukawa E. , Hashimoto B.
Published: May 2008

A new 90-deg bend shape has been developed for erosion resistance. The design consists of a gradually expanding inlet, a large-diameter curved section, and a gradually contracting outlet. Tests were conducted using alumina particles in air at an average velocity of 27 m/s, passing through a carbon steel bend. The new bend design had an erosion life exceeding 4000 hr, compared to 38 hr for a conventional bend design.
Fine Structure of Vortex Sheet Rollup by Viscous and Inviscid Simulation
Authors: Tryggvason G. , Dahm W. J. A. , Sbeih K.
Published: May 2008

Numerical simulations of the large amplitude stage of the Kelvin-Helmholtz instability of a relatively thin vorticity layer are discussed. At high Reynolds number, the effect of viscosity is commonly neglected and the thin layer is modeled as a vortex sheet separating one potential flow region from another. Since such vortex sheets are susceptible to a short wavelength instability, as well as singularity formation, it is necessary to provide an artificial “regularization” for long time calculations. We examine the effect of this regularization by comparing vortex sheet calculations with fully viscous finite difference calculations of the Navier-Stokes equations. In particular, we compare the limiting behavior of the viscous simulations for high Reynolds numbers and small initial layer thickness with the limiting solution for the roll-up of an inviscid vortex sheet. Results show that the inviscid regularization effectively reproduces many of the features associated with the thickness of viscous vorticity layers with increasing Reynolds number, though the simplified dynamics of the inviscid model allows it to accurately simulate only the large scale features of the vorticity field. Our results also show that the limiting solution of zero regularization for the inviscid model and high Reynolds number and zero initial thickness for the viscous simulations appear to be the same.
Effect of Freestream Velocity on the Three-Dimensional Separated Flow Region in Front of a Cylinder
Authors: Eckerle W. A. , Awad J. K.
Published: May 2008

Details of the horseshoe vortex formation around a cylinder were studied to determine the flow parameters that affect the flow separation in front of the cylinder. An experimental setup consisting of a circular cylinder vertically mounted on the floor of the wind tunnel test section was assembled. The approaching turbulent boundary layer was four centimeters thick. Pressures were measured on the cylinder surface and the tunnel floor with surface static pressure taps. Surface flow visualizations were accomplished to locate singlar points and the size of separation region on the endwall surface. Interior mean and fluctuating velocity data and Reynolds stresses in front of the cylinder were nonintrusively measured with a two-component Laser Doppler Anemometer system. Freestream stagnation at the endwall/cylinder surface occurred in all cases, but two types of separation were identified in this investigation. The flow pattern in the separation region depends on the freestream momentum and the boundary layer displacement thickness. A large-scale fully developed vortex was formed in the plane of symmetry for low approaching freestream velocities. A fully developed vortex was not present at higher approach velocities. Maximum production of turbulent kinetic energy was measured around the core of the vortex when fully formed.
Wake Characteristics of Two Circular Cylinders Arranged Perpendicular to Each Other
Authors: Fox T. A.
Published: May 2008

The turbulent fluid motion established in the wake of two long, smooth circular cylinders arranged perpendicular to each other has been investigated in a steady, low-turbulence, uniform flow at Reynolds numbers of 2×104 and 2×103 (based on cylinder diameter and freestream velocity). A complex three-dimensional regime was found at the center of the configuration, the precise nature of which is dependent upon the spacing of the cylinders. If the distance between the axis of each cylinder is less than three diameters, the fluid motion in the central near wake is dominated by secondary flows associated with trailing vortices and horseshoe vortices, whereas at spacings beyond this critical value there is a considerable reduction in the influence of secondary flow. The paper examines these spacing related regimes in detail and considers the extent of the associated interference effects.
Separation Control: Review
Authors: Gad-el-Hak Mohamed , Bushnell Dennis M.
Published: May 2008

Under certain conditions, wall-bounded flows separate. To improve the performance of natural or man-made flow systems, it may be beneficial to delay or advance this detachment process. The present article reviews the status and outlook of separation control for both steady and unsteady flows. Both passive and active techniques to prevent or to provoke flow detachment are considered and suggestions are made for further research.
Turbulent Flow Around a Bluff Rectangular Plate. Part II: Numerical Predictions
Authors: Djilali N. , Gartshore I. S. , Salcudean M.
Published: May 2008

This paper presents calculations of the time-averaged separated-reattaching flow around a bluff rectangular plate, using a finite difference procedure and the k-ε turbulence model. Two discretization methods are used: the hybrid differencing scheme, and the bounded skew hybrid differencing scheme. The latter, although superior to the former for all grid distributions, results in a reattachment length about 30 percent shorter than the measured value. When a modification which takes into account streamline curvature is incorporated into the k-ε model, a marked improvement in the predictions is obtained. A reattachment length of 4.3 plate thicknesses (D), compared to an experimental value of 4.7D, is obtained, and the predicted mean flow field, turbulent kinetic energy and pressure distributions within the separation bubble are found to be in good agreement with experiments.
Real-Time Video Analysis of Twin Jets in a Crossflow
Authors: Savory E. , Toy N.
Published: May 2008

The research presented in this paper is an investigation of the interaction between twin side-by-side circular jets issuing into a crossflow, utilizing a real-time video digitization system to obtain quantitative data from the visualized flow fields. The intermittency field results obtained from experiments with different jet spacings and jet velocity/crossflow velocity ratios are reported.
Experimental Analysis and Flow Visualization of a Thin Liquid Film on a Stationary and Rotating Disk
Authors: Thomas S. , Faghri A. , Hankey W.
Published: May 2008

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0–300 rpm and the flow rate varied from 7.0–15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.
An Experimental Investigation of Butterfly Valve Performance Downstream of an Elbow
Authors: Morris M. J. , Dutton J. C.
Published: May 2008

The results of an experimental investigation concerning the operating characteristics of a butterfly valve downstream of a mitered elbow are reported. Primary emphasis is given the influences of valve disk angle, valve/elbow spacing, and valve/elbow orientation on the dimensionless pressure drop, mass flow coefficient, and aerodynamic torque coefficient characteristics of the valve. The results show that when the valve is located two pipe diameters downstream of the elbow, the performance characteristics are substantially affected by the relative valve/elbow orientation. However, at a spacing of eight diameters the effect of the elbow on the valve operating characteristics is small.
Viscosity Flow Correction for Small Control Valve Trim
Authors: Baumann H. D.
Published: May 2008

A valve sizing method is developed to permit the correct selection of the size of small flow control valve trim handling minute flowing quantities. Most valves such as these operate primarily in laminar or transitional flow regimes, with either gaseous or liquid fluids, due to the geometries involved. The proposed sizing method can be combined with existing turbulent flow equations by the establishment of a valve style modifier Fd which describes the correct relationship between the hydraulic diameter and the equivalent single orifice diameter of a specific valve trim, thereby permitting calculation of the correct Reynolds number for a given flow condition. Finally, a correction factor FR is used which permits necessary flow corrections when used in connection with the correct valve Reynolds number. This method appears to be reasonably accurate and validated to the extent that the experimental data permit.
Suction Reverse Flow in an Axial-Flow Pump
Authors: Alpan K. , Peng W. W.
Published: May 2008

Experiments are carried out to determine the effects of different inlet geometries on the onset of suction recirculation and its associated power consumption in an axial-flow pump. The critical flow rate is determined by both the “string” visual technique and “pressure” method. The results are correlated with the inlet area and flow velocity distribution upstream of the impeller. Four different conical covers matching the impeller leading edge are employed to cover the impeller inlet completely or partially. Covering the inlet area reduces the critical flowrate corresponding to the onset of suction recirculation and eliminates all recirculation at higher flowrates. The power consumption associated with the suction recirculation flow for the uncovered impeller is determined by comparing the shaft powers with and without inlet covers. At the shut-off condition, the power is estimated from a comparison with the shaft power measured with the impeller inlet completely covered. Experimental studies conclude that the power consumption due to suction recirculation is mainly controlled by the impeller inlet area and is insensitive to the inlet pipe configuration. At shut-off condition, the power coefficient correlates well with the parameter based on the hydraulic radius of inlet area. At a finite through flowrate the analytical model recommended by Tuzson (1983) is adequate, except for a proportionality coefficient determined from the test data.
General Correlations and Selection Procedures for Flow in Polyethylene Tubes With Uniformly Spaced Wall Orifices
Authors: Brundrett E.
Published: May 2008

A previously described experimentally based numerical procedure is used to characterize the flow in thin walled polyethylene tubes with uniformly spaced wall orifices (polytubes). The procedure evaluates the required supply pressure for specified geometry, supply flow, and supply swirl angle; and then predicts the pressure and discharge profiles along the polytube. The predicted values are in good agreement with reported experimental results and are used to develop a data base of the most significant ranges of polytube and supply parameters. Then, explicit design correlations and recommendations are obtained for satisfactory and economical performance.
Review—Vortex Shedding Lock-on and Flow Control in Bluff Body Wakes
Authors: Griffin O. M. , Hall M. S.
Published: May 2008

The results of recent experiments demonstrate that the phenomenon of vortex shedding resonance or lock-on is observed also when a bluff body is placed in an incident mean flow with a periodic component superimposed upon it. This form of vortex shedding and lock-on exhibits a particularly strong resonance between the flow perturbations and the vortices, and provides one of several promising means for modification and control of the basic formation and stability mechanisms in the near-wake of a bluff body. Examples are given of recent direct numerical simulations of the vortex lock-on in the periodic flow. These agree well with the results of experiments. A discussion also is given of vortex lock-on due to body oscillations both normal to and in-line with the incident mean flow, rotational oscillations of the body, and of the effect of sound on lock-on. The lock-on phenomenon is discussed in the overall context of active and passive wake control, on the basis of these and other recent and related results, with particular emphasis placed on active control of the circular cylinder wake.
Some Aspects of Uncertainty in Computational Fluid Dynamics Results
Authors: Mehta U. B.
Published: May 2008

Uncertainties are inherent in computational fluid dynamics (CFD). These uncertainties need to be systematically addressed and managed. Sources of these uncertainties are identified and some aspects of uncertainty analysis are discussed. Some recommendations are made for quantification of CFD uncertainties. A practical method of uncertainty analysis is based on sensitivity analysis. When CFD is used to design fluid dynamic systems, sensitivity-uncertainty analysis is essential.
A Numerical Model to Predict the Nonlinear Response of External Flow Over Vibrating Bodies (Planar Flow)
Authors: Venkat N. Kolluru , Spaulding Malcolm
Published: May 2008

A model is developed to simulate two-dimensional laminar flow over an arbitrarily shaped body, a portion of which is subjected to time varying harmonic motion. The model is tested by comparison to previous numerical simulations for flow over a square cavity, oscillatory flow through a wavy channel and boundary layer flow along a flat plate. The model is applied to predict the flow over a flat plate with a section forced in simple sinusoidal motion. The dimensionless vibration amplitude, H0, and the Reynolds number, Re are maintained at 0.1 and 1000, respectively. The Strouhal number, St, defined as the ratio of the flow advective time scale to the plate oscillation period, is varied in the range 0.0 ≦ St ≦ 1.0. The friction and pressure coefficients over the vibrating portion of the body are analyzed using Fast Fourier Transform techniques. For low frequency vibrations (low Strouhal number) the pressure and friction coefficients match the steady state results for flow over a fixed sinusoidal bump. A small amplitude pressure wave generated by the oscillating plate propagates downstream with the flow. For high frequency vibrations (high Strouhal number) the pressure and friction coefficients over the vibrating portion of the body deviate from the steady state results and a high amplitude pressure wave propagates downstream. The pressure at one chord length upstream is also affected. As St increases the flow becomes highly nonlinear and harmonics appear in the downstream velocity and pressure fields. The nonlinearity is controlled by the convective acceleration term near the vibrating plate surface.
Numerical Analysis of Laminar Flow in Curved Elliptic Ducts
Authors: Dong Z. F. , Ebadian M. A.
Published: May 2008

The complete form of the Navier-Stokes equations is solved in this paper for a steady, incompressible, fully developed laminar flow in a curved duct of elliptic cross section. This is achieved by the use of the control volume-based finite difference method via the numerically generated boundary fitted coordinate system. The curvature ratio is included in the primitive variable governing equations, which are solved based on the SIMPLE algorithm. Solutions are obtained for the minor-axis to major-axis ratios of the elliptic duct, 0.2, 0.5, and 0.8, and for Dean numbers ranging from 11.41 to 635.7. It is found that only one pair of vortices appears on the cross-section, even at a Dean number of 635.7. The friction factor and the ratios of the curved duct to straight duct are tabulated and the correlation equation is developed. Furthermore, the distribution of the axial velocity is displayed graphically to illustrate its variations with the Dean number and the minor-axis to major-axis ratio of the elliptic duct on the horizontal symmetry line and on the half-vertical symmetry line. The present method is also applied to solve for a fully developed laminar flow in a curved square flow. The results are compared with the data available in the literature and very close agreement is observed.
A Numerical Study of Laminar 90-Degree Bend Duct Flow With Different Discretization Schemes
Authors: Yeo R. W. , Wood P. E. , Hrymak A. N.
Published: May 2008

Three different discretization schemes were used to study the flow in a 90-degree bend square duct. The numerical method consists of a general curvilinear coordinate formulation of the governing equations and a non-staggered grid for the variables. A stable method of implementing the higher-order schemes is proposed. The second-order upwinding and QUICK schemes give results which compare more favourably with the experimental data than the first-order upwinding method. In 3-D flow problems, the grid-refinement is severely limited by the amount of computer storage and the use of higher-order upwinding schemes provides a better alternative in obtaining accurate flow predictions.
Improving Zielke’s Method of Simulating Frequency-Dependent Friction in Laminar Liquid Pipe Flow
Authors: Suzuki Katsumasa , Taketomi Takayuki , Sato Sanroku
Published: May 2008

Zielke’s technique of using a method of characteristics to simulate transient phenomena of a liquid transmission line is accurate, easy to apply to complicated systems and therefore, frequently used. However, it requires a very large amount of computation time and computer storage to simulate frequency-dependent friction in a transient liquid flow. Searching for a way to counteract these disadvantages, the authors took note of the fact that the weighting function, which is the root of the above problems, is given by exponential functions or other functions depending on dimensionless time. In order to perform mathematically equivalent calculation without approximations, they have developed a new method which requires much less computation time and computer storage than Zielke’s method. The calculation process is shown by a block diagram to facilitate visual understanding of the method.
Laminar Flow Over Wavy Walls
Authors: Patel V. C. , Chon J. Tyndall , Yoon J. Y.
Published: May 2008

The boundary layer over a wavy wall and fully-developed flow in a duct with a wavy wall are considered. Numerical solutions of the Navier-Stokes equations have been obtained to provide insights into the various steady flow regimes that are possible, and to illustrate the nuances of predicting flows containing multiple separation and reattachment points.
Turbulent Flow in a Channel With a Wavy Wall
Authors: Patel V. C. , Chon J. Tyndall , Yoon J. Y.
Published: May 2008

A numerical method for the solution of the Reynolds-averaged Navier-Stokes equations, together with a two-layer turbulence model, has been used to describe steady flow in a two-dimensional channel with a wavy wall. Comparisons of calculations with experiments demonstrate the effects of alternating pressure gradients induced by alternating surface curvatures, and multiple separations and reattachments. The numerical method and the turbulence model are shown to capture the overall features of such a flow, including the breakdown of the logarithmic law of the wall in strong pressure gradients and in separated flow.
Application of V Shape Riblets to Pipe Flows
Authors: Nakao Shin-ichi
Published: May 2008

Pipes with V shape riblets were tested at Reynolds numbers between 5×103 and 4×104. All riblet pipes indicated some drag reduction. The model with h = 0.55 mm and h/S = 0.483 showed the maximum drag reduction of 8 percent and the widest range of Reynolds number over which the riblet reduces drag. The riblet shape desirable for drag reduction in pipe flows was almost the same as that in flat plate boundary layers, but the value of S+ which provided the maximum drag reduction was quite different; S+ = 23 for pipe flows and S+ = 12 for flat plate boundary layers.
Effect of Suction on the Stability of Supersonic Boundary Layers. Part II—First-Mode Waves
Authors: Masad J. A. , Nayfeh A. H. , Al-Maaitah A. A.
Published: May 2008

The effect of suction on the first mode of instability of compressible two-dimensional boundary layers is investigated. Suction is found to be more effective in stabilizing the viscous instability, and hence it is more effective at low Mach numbers. Suction decreases the amplification rates at all frequencies and narrows down the band of unstable frequencies. Moreover, for a given frequency, suction decreases the amplification rates at all streamwise locations. Variations of the growth rates of the most amplified first-mode waves with mass flux are found to be almost linear.
Direct Determination of the Onset of Transition to Turbulence in Flow Passages
Authors: Obot N. T. , Jendrzejczyk J. A. , Wambsganss M. W.
Published: May 2008

Easily applied methods are proposed, based on tests with air and water, for direct determination of the onset of transition in flow passages using static and dynamic wall pressure data. With increasing Reynolds number from laminar flow, the characteristic feature of transition is the change from steady to oscillating pressure readings. It is established that the power spectral density (psd) representations exhibit a distinctive change in profile at transition. Further, it is shown that the root-mean-square (rms) values of the wall pressure fluctuations rise sharply at transition. The critical Reynolds numbers recorded via the change from steady to unsteady pressure readings are almost the same as those deduced from the psd and rms pressure data or from the familiar friction factor-Reynolds number plots.
Prediction of Three-Dimensional Developing Turbulent Flow in a Square Duct With an Anisotropic Low-Reynolds-Number k-ε Model
Authors: Myong Hyon Kook , Kobayashi Toshio
Published: May 2008

Three-dimensional developing turbulent flow in a square duct involving turbulence-driven secondary motion is numerically predicted with an anisotropic low-Reynolds-number k-ε turbulence model. Special attention has been given to both regions close to the wall and the corner, which are known to influence the characteristics of secondary flow a great deal. Hence, the no-slip boundary condition at the wall is directly used in place of the common wall function approach. The resulting set of equations simplified only by the boundary layer assumption are first compared with previous algebraic stress models, and solved with a forward marching numerical procedure for three-dimensional shear layers. Typical predicted quantities such as mean axial and secondary velocities, friction coefficients, turbulent kinetic energy, and Reynolds shear stress are compared with available experimental data. These results indicate that the present anisotropic k-ε turbulence model performs quite well for this complex flow field.