bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Characterization of Radiation and Pollutant Emissions of Biodiesel and Hydrocarbon Liquid Fuels
Authors: Love N. D. , Parthasarathy R. N. , Gollahalli S. R.
Published: February 2009

As a result of decreasing petroleum supplies, new fuel sources, such as transesterified biofeedstock based oils and their blends with petroleum diesel fuels, have emerged with potential to partially replace conventional diesel and gasoline fuels. Although these fuels have shown some promising results in engine studies, their basic combustion properties have not been well documented. Also, research is underway to develop new fuels from other sources or by altering their molecular structure to be fungible with conventional fuels. Thus, there is a need for tests to characterize the combustion and emission properties of these new liquids, which are available only in small quantities at the research and development stage. This paper deals with a technique that meets those goals. The fuel was prevaporized and mixed with air and burnt in a tubular burner (9.5 mm inner diameter) at atmospheric pressure under laminar conditions. A pilot methane/air flame was used as the ignition source. The test conditions were so chosen that the measured properties could be attributed primarily to the fuel chemical structure. Several liquid fuels were tested, including commercially available petroleum-based No. 2 diesel fuel, canola methyl ester (CME B100) biodiesel, kerosene, methanol, toluene, and selected alkanes. The radiative heat flux from the flames was measured using a wide-angle pyrheliometer; the emissions from the flames were sampled to measure the concentration of CO, CO2, and NO. The measured radiant heat fraction values and the emission indices of NO and CO of both petroleum-derived and biofuels agreed well with those found in literature; thus, the feasibility of this method to rapidly characterize the combustion and emission properties of new liquids, such as biofuels, is demonstrated.
Growth Randomness, Porosity, and Surface Coverage of Carbon Films
Authors: Tang Huan , Ma Xiaoding , Thangaraj Raj , Gui Jing
Published: February 2009

Mathematical models that describe the static growth processes of sputtered and ion-beam deposited amorphous carbon films are established. Two important factors are considered in deriving the models: the film porosity and the growth randomness. The growth randomness for both hydrogenated sputter carbon and hydrogenated ion-beam carbon films are deduced from the film roughness vs. film thickness data obtained from X-ray reflectometry. The porosities of the two types of films are estimated from the experimentally determined values of film densities and sp3/sp2 C–C bonding ratios. The derived film growth models, which find support from a surface coverage experiment, have allowed us to predict the surface coverage of the two types of carbon films in the thickness range of interest. We find that, neglecting intermixing at the substrate/carbon interface, the denser ion-beam carbon films are nearly as effective at achieving a similar level of surface coverage as the less dense sputter carbon films at twice the thicknesses. Our surface coverage model points to further increasing the carbon film density as the most effective approach for the continued reduction in the carbon overcoat thickness while maintaining adequate surface coverage.
Time-Frequency Analysis of Slider Dynamics and the Effect of Lubricant
Authors: Deoras Saurabh K. , Talke Frank E.
Published: February 2009

The dynamics of pico sliders is investigated during scratch impact using laser Doppler vibrometry. Airbearing frequencies and damping of the pitch frequency are studied as a function of disk velocity for lubricant thickness values of 1.6nm, 1.0nm and 2.0nm. In addition, time-frequency analysis is used to study transient events during slider-scratch impact. The results indicate that the slider dynamics is not only a function of the design of the air-bearing, but also of the velocity and the characteristics of the lubricant film thickness on the disk surface.
Dynamic Analysis of Sliding Contacts at Head-Disk Interface
Authors: Chuang T.-J. , Hsu S. M.
Published: February 2009

As magnetic data storage technology moves towards higher areal data density with higher rotational speeds and lower flying heights, the propensity of severe sliding contacts at the head-disk interface is bound to increase. The tribological performance of the head-disk interface will have significant impact on the durability and service life of the hard disk drive (HDD). A 3D finite element model is constructed to simulate the high speed impact event of a slider on the disk surface. For a given design of the disk with known layer thicknesses and properties, as well as that of the slider with its surface texture, the model predicts contact zone, depth force and duration as well as time-history of energy transfer and its partition, substrate stress and plastic zone for a given impact velocity. The effects of the material properties and layer thicknesses on the performance of the HDD are investigated.
Modeling of the Onset of Gas Entrainment From a Stratified Two-Phase Region Through Two Side Branches
Authors: Ahmed M. , Lenard K. , Hassan I. , Esmail N.
Published: February 2009

A theoretical analysis for the onset of gas pull-through (entrainment) during discharge from a stratified two-phase region through two vertically aligned side branches has been developed in this paper. Initially, a simplified point-sink model was developed; this was followed by the acquisition of a more accurate finite branch model. The predicted value of the critical height at the onset of gas entrainment was found to be a function of each branches’ corresponding Froude number (Fr1 and Fr2), as well as the ratio between the vertical distance connecting the centerlines of the two branches and the diameter of the branches (L/d). The predicted values of the critical heights were found to be consistent with the corresponding experimental data at different values of Fr1, Fr2 and L/d. From the basis of the present models, it was established that when increasing the flow through the lower branch, the critical height increased for all values of Fr1 and L/d. In addition, it was found that increasing the vertical distance between the two branches, reduced the effects of the lower branch on the determination of the critical height.
Development of Numerical Code to Predict Three-Dimensional Sand Erosion Phenomena
Authors: Junichi Kuki , Toda Kazuyuki , Yamamoto Makoto
Published: February 2009

This paper presents a numerical procedure to predict a three-dimensional sand erosion phenomenon and the interaction between the flow field and the eroded surface. To simulate this phenomenon, the turbulent flow field, the particle trajectory and the amount of erosion on the eroded wall are calculated repeatedly. In computations of the flow field, compressible Navier-Stokes equations and low-Reynolds-number type k–ε turbulence model are adopted. Assuming that the concentration of suspended particle is dilute, particle-particle collision and the influence of particle motions on the flow field are neglected. The Neilson-Gilchrist erosion model is used to estimate the weight loss due to erosion. To verify the developed code, two types of 90-degree bends are computed. The results show that the present procedure can reasonably reproduce the sand erosion process and the temporal change of both the flow field and the wall surface qualitatively.
Study of the 90° Elbows Performance as Phase Separators in an Air-Water Two-Phase Flow
Authors: Herna´ndez P. Valente , Sa´nchez S. Florencio , Toledo V. Miguel , Polupan Georgiy
Published: February 2009

In order to observe the 90° elbows performance as phase separators in an air-water two-phase flow, experimental results for the phase split which occurs at a 90° branched elbow are presented. The branched elbow geometry was varied in order to have three (branch diameter / elbow diameter) ratios and three branch inclination angles. Also the pressure was monitored at different points of the elbow with ramification in order to examine the pressure drop effect. The flow pattern upstream was mainly slug flow. First, the analysis of the main independent variables effect, (superficial velocities, branch inclination angle, ratio of diameters and pressure gradients) was carried out, then a correlation for the phase split was developed and, finally a comparison was made with data of phase separation in T junctions obtained by Azzopardi [1] and Soliman [2], as a result, a better behavior as phase separator was found for the elbow.
Oscillatory Flow of a Magnetic Fluid in a Pipe at Low Frequency Range Under a Magnetic Field: Phase Difference of Pressure
Authors: Shimada Kunio , Shuchi Shigemitsu , Kamiyama Shinichi
Published: February 2009

We made on numerical analysis of phase difference between pressure along the pipe axis and given oscillatory flow velocity in an straight pipe under a nonuniform steady magnetic field. In the analysis, a few cases under the assumption of numerical condition were conducted on: the first is taking into account the least compressibility of the fluid with using the obtained experimental data of the bulk modulus, the second taking into account the nonuniform distribution of mass concentration of particles, and the thrid taking into account the aggregation with the number of aggregated particles proposing as a prorate spheroid. By considering the three effects of the least compressibility and the nonuniform distribution of mass concentration, the aggregation as a prorate spheroid, the phase difference varies quantitatively at the lowest Womersley number range. And then, the numerical results were compared with the experimental data.
Velocity Profile Measurement of an Oscillating Pipe Flow of a Magnetic Fluid
Authors: Oshikawa Yuki , Innami Takashi , Sawada Tatsuo
Published: February 2009

Since UVP is the method to take the velocity information by using ultrasound, this method is very suitable for measuring the velocity profile of opaque fluid. Oscillating pipe flow of a magnetic fluid was investigated experimentally to examine the applicability of this method to magnetic fluid flow. We used a diluted water-base magnetic fluid and the magnetic field was applied by two permanent magnets. Influence of an applied magnetic field on flow behaviors were discussed. The amplitude and phase of the oscillating velocity varied with intensity of the magnetic field, which yielded increase of the apparent viscosity.
Rheology and Behavior of Magnetic Fluids in Alternating/Rotating Magnetic Fields
Authors: Rinaldi Carlos , He Xiaowei , Rosenthal Adam , Franklin Thomas , Lorenz Cory , Zahn Markus
Published: February 2009

The rheology and behavior of magnetic fluids in the presence of time-varying magnetic fields is illustrated through three sets of experiments. The first involves measurements of ferrofluid torque on a cylindrical spindle under applied uniform rotating magnetic fields. We measure the torque required to restrain a stationary cylindrical test wall in contact with aqueous ferrofluids subjected to the rotating uniform magnetic field generated by a three-phase AC 2-pole motor stator winding. The torque is found to scale linearly with volume, and to be a function of the applied magnetic field amplitude, frequency and direction of rotation. Measurements show that for ferrofluid entirely inside the cylindrical test wall the torque points in the same direction as the magnetic field rotation pseudovector, whereas for ferrofluid entirely outside the cylindrical wall the torque points in the direction opposite to the field rotation pseudovector. The second set of experiments explores the formation of ordered ferrofluid structures in the gap of a Hele-Shaw cell subjected to simultaneous vertical DC and in-plane horizontal rotating magnetic fields. Finally, the third set of experiments illustrates the effect of applied DC fields on the shape of ferrofluid jets and sheets.
Jet Aeroacoustic Research at NASA (Keynote Paper)
Authors: Kinzie Kevin W. , Bridges James E.
Published: February 2009

An overview of NASA’s jet aeroacoustic research is provided here along with a description of NASA’s current and recent focused aircraft acoustic programs. These programs are designed to advance jet noise reduction technology through a balanced investigation of jet noise reduction concepts, understanding the fundamentals of jet flows and turbulence, and developing physics-based tools that predict jet flowfields and associated noise. Jet noise goals for these programs are highlighted with examples of key jet noise technologies.
Fluid Dynamic Challenges in Severe Service Control Valves (Keynote Paper)
Authors: Sherikar Sanjay V.
Published: February 2009

Three areas of practical interest relating to flow in valves are addressed: cavitation, flow-induced vibration and noise. Such conditions are common when pressure drop across the valves is high and result in unsatisfactory behavior of the systems. Valve industry background in each of these areas is discussed briefly. The success in eliminating cavitation in valves is described. Reliable quantitative prediction of vibration and noise in valves is still a formidable challenge. Experimental work to understand some of the fundamental mechanisms in these two areas is presented.
Quasi Three-Dimensional Analysis of Cavitation in an Inducer
Authors: Horiguchi Hironori , Arai Souhei , Fukutomi Junichiro , Nakase Yoshiyuki , Tsujimoto Yoshinobu
Published: February 2009

A quasi three-dimensional analysis of steady cavitation in a herical inducer is carried out by a method based on the assumption that the fluid is inviscid and the stream surface is rotationally symmetric. The analysis in the meridian plane are combined with that in blade-to-blade stream surface where a singularity method is used based on a closed cavity model. It was found that the influence of the three-dimensionality of the flow on cavitation mainly appears as the change of angle of attack associated with the change of meridian velocity caused by the movement of meridian streamline in radial direction.
Bulk Carbon Nanotubes for Micro Anemometry (Invited Paper)
Authors: Wong Victor T. S. , Li Wen J.
Published: February 2009

We have successfully developed a process to manipulate post-growth multi-walled carbon nanotube (MWNT) by AC electrophoresis to form resistive elements and showed that these elements can potentially served as novel sensing elements for micro/nano thermal and anemometry sensing. We have measured the temperature coefficient of resistance (TCR) of these MWNT bundles and integrated them into constant current mode configuration for dynamic characterization. Preliminary experimental measurements showed that the devices could be operated in micro-watt power range for micro thermal and anemometry sensing. This operation range is three orders of magnitude lower than conventional Micro-Electro-Mechanical Systems (MEMS) polysilicon sensors in constant current (CC) mode configuration. In addition, the devices exhibited very fast frequency response (> 100 kHz) in CC mode. Based on these results, we are currently developing polymer-based MWNT embedded sensor for various micro/nano fluidic applications.
Vortex Control by an Artificial Muscle Based on the Conducting Polymer
Authors: Fuchiwaki Masaki , Tanaka Kazuhiro , Sewa Shingo , Onishi Kazuo
Published: February 2009

We have proposed the flow control by using an artificial muscle based on the conducting polymer. In order to utilize the artificial muscle for flow control, it is important to clarify the mechanical properties on the artificial muscle based on the conducting polymer. The purpose of this study is to clarify the mechanical properties on artificial muscle and possibility of flow control by using it. We have measured the tensile force generated by artificial muscle in the distilled water. Moreover, we have observed the actuation of artificial muscle based on the conducting polymer in water tunnel. The tensile force of artificial muscle increased as the electrode potential increased. The averaged maximum tensile force did not depend on the scan rate of electrode potential. It depended on the electrode potential and was almost constant. However, the time for reaching maximum tensile force depended on the scan rate. The artificial muscle performed the bending actuation sufficiently not only static water but also running water. Therefore, it can be considered that the artificial muscle will be applied to the actuator for flow control.
Numerical Simulation of Supersonic Flow and Particle Motion in Aerodynamic Lenses
Authors: Abouali Omid , Ahmadi Goodarz
Published: February 2009

Airflow and particle motions in aerodynamic lenses are studied. The computational grid is generated with the use of GAMBIT code and FLUENT 5 is used in the analysis. The axisymmetric compressible form of the Navier-Stokes equation is solved and the airflow conditions are evaluated. One-way coupling is assumed in that the air transports the particles, but the effect of dilute particle concentrations on flow field is ignored. The particle equation of motion including drag, lift and Brownian forces is used and the particle trajectories in the aerodynamic a lens are analyzed. In addition, the airflow field and particles motions downstream of the nozzle are also studied. A series of sensitivity analyses on the effect of inlet flow stagnation pressure and backpressure of the nozzle on the aerodynamic performance of the lens is performed. Sample streamlines and particles trajectories in an axisymmetric plane of a combination of three aerodynamic lenses and a nozzle are shown in the figures.
Shock Waves and Plume Prediction of a Rocket Thruster With an Attached Panel
Authors: Davoudzadeh Farhad , Liu Nan-Suey
Published: February 2009

Reynolds-Averaged Navier-stokes (RANS) numerical simulations are performed to predict the supersonic flow field induced by a H2-O2 rocket thruster with an attached panel, under a variety of operating conditions. The simulations have captured physical details of the flow field, such as the plume formation and expansion, formation of a system of shock waves and their effects on the temperature and pressure distributions on the walls. Comparison between the computed results for 2-D and adiabatic walls and the related experimental measurements for 3-D and cooled walls shows that the results of the simulations are consistent with those obtained from the related rig tests.
3D-Flow Structures Behind Truncated Circular Cylinders
Authors: Leder Alfred
Published: February 2009

An experimental investigation of the two flows around finite circular cylinders with different head geometries mounted on a flat plate, see fig. 1, is reported. The aspect ratio L/D (with length L and diameter D) of both cylinder models is 2.0. The focus of this study is toward examining the complex separated flow structures and wake properties as well as the influence of the head geometry on the flow characteristics. Velocity and turbulence measurements have been carried out with a three component Laser Doppler anemometer (LDA) at the Reynolds number ReD = 2.0 · 105. The experimental results show complex 3D fluid motions in the regions of separated flow. They are induced by the superposition of three main vortical flows. The developing vortex and turbulence structures for both investigated models show similar overall features. Differences in the geometries of the 3D-envelopes of the recirculating flow as well as in the distributions of turbulent terms can be allocated to differences in the vortical flows over the free end surfaces of the cylinders.
Numerical Analysis of the Effects of Lifting Surface Contamination on Aircraft Aerodynamics
Authors: Su Jichao
Published: February 2009

PMAL3D, the Aerodynamics Laboratory’s in-house panel method program coupled with a boundary layer code, has been improved in dealing with various three-dimensional configurations. Three different configurations have been studied with this improved program. They are Fokker F-28 MK1000 aircraft with aileron deflections, a NASA LS(1)-0417 configuration (a wing/flap combination) and a NACA 4415 airfoil. The aerodynamic effects of contaminated lifting surfaces of the F-28 have been analyzed and discussed in detail. PMAL3D’s ability to match experimental or flight data wherever available and its reliable predictive capability make it a valuable practical engineering tool. The in-house program was further assessed through its applications to the NASA LS(1)-0417 configuration and the NACA 4415 airfoil.
Study on Performance and Internal Flow of Cross-Flow Wind Turbine
Authors: Takeuchi Kazuki , Fukutomi Junichiro , Kodani Hidetoshi , Horiguchi Hironori
Published: February 2009

The wind turbine has become more popular in recent years, but on the other hand, the developments of small wind-turbine have been legging behind. Because, the energy density of wind is small, since the efficiency of the main part of a wind turbine is very low. The construction costs become comparatively high-priced. Then, the main part of this subject is to show that, by collecting and sucking out more winds, a wind turbine is made to pass many winds and the new cross-flow wind turbine that increases an output coefficient is proposed. The cross-flow wind turbine has high torque and low speed characteristics and the structure are very simple. So, it can be used in a large wind velocity region. However, even if the power coefficient is high, it is about 10%. The purpose of this paper is to show how we can improve the power coefficient by applying a casing, which has a nozzle and a diffuser. This research was made to clear up fundamental characteristics of the interaction between outer flow and inner flow. Three kinds of cross-flow wind turbines were designed. The nozzle and diffuser have been designed suitable for the performance of wind turbine. The flow simulations by CFD have been carried out for various types of casings at 20 m/s with Fluent Ver5.0. All Wind tunnel experiments were performed at 20m/s. The case of casing 2, which have plate arranged near the separation point of cylinder, also experimented. The rotor that is settled in the casing 1 shows a larger power coefficient than the case without a casing. The casing of the cross-flow turbine makes a pressure difference between inflow and outflow. The pressure difference increases the mass flow rate. Therefore much more wind passes through into the cross-flow turbine. In this experiment, the power coefficient increased 1.5 times in the case with casing. A still higher output coefficient could be obtained in the case where it is shown by the casing 2.
Calculation of Hydrodynamic Forces and Flow Induced Vibrations of Centrifugal Sewage Water Pumps
Authors: Benra Friedrich-Karl , Dohmen Hans Josef , Schneider Oliver
Published: February 2009

The interaction of the flow in the impeller and the casing of centrifugal pumps leads to periodically unsteady pressure distributions in the casing. The resulting unsteady forces affect the impeller and produce radial deflections of the pump shaft. These oscillations of the rotor are periodic with the turning frequency times the blade number. Especially pumps with small blade numbers (for example single-blade and double-blade impellers) which are often used for the sewage transport have very strong pressure changes within one impeller revolution and therefore often show extreme vibration amplitudes at the blade passing frequency. The present contribution describes the calculation of the hydrodynamic excitation forces in a sewage water pump which can be alternatively equipped with a single-blade and a double-blade impeller by numerical simulation of the three-dimensional, viscous and unsteady flow for several operating points. Subsequently the resulting vibration amplitudes are determined by a transient analysis of the pump rotor system using a commercial FEM-Method. With the so known pressure field and vibration amplitudes the vibration behavior of sewage water pumps can be influenced already during the design by changing the relevant parameters.
Numerical Prediction of Critical Cavitation Performance in Hydraulic Turbines
Authors: Kurosawa Sadao , Matsumoto Kiyoshi
Published: February 2009

In this paper, numerical method for predicting critical cavitation performance in a hydraulic turbine is presented. The prediction method is based on unsteady cavitation flow analysis to use bubble two-phase flow model. The prediction of the critical cavitation performance was carried out for the aixal hydraulic turbine and the francis turbine as a typical examples. Results compared to the experiment showed a good agreement for the volume of cavity and the performance drop off and it was recognized that this method could be used as an engineering tool of a hydraulic turbine development.
Investigation of Internal Cooling Air Flow of Gas Turbines With Attention to Heat Transfer
Authors: Brillert D. , Benra F.-K. , Dohmen H. J. , Schneider O.
Published: February 2009

The cooling air in the secondary air system of gas turbines is routed through the inside of the rotor shaft. The air enters the rotor through an internal extraction in the compressor section and flows through different components to the turbine blades. Constant improvements of the secondary air system is a basic element to increase efficiency and power of heavy duty gas turbines. It is becoming more and more important to have a precise calculation of the heat transfer and air temperature in the internal cooling air system. This influences the cooling behavior, the material temperature and consequently the cooling efficiency. The material temperature influences the stresses and the creep behavior which is important for the life time prediction and the reliability of the components of the engine. Furthermore, the material temperature influences the clearances and again the cooling flow, e.g. the amount of mass flow rate, hot gas ingestion etc. This paper deals with an investigation of the influence of heat transfer on the internal cooling air system and on the material temperature. It shows a comparison between numerical calculations with and without heat transfer. Firstly, the Navier-Stokes CFD calculation shows the cooling flow physics of different parts of the secondary air system passages with solid heat transfer. In the second approach, the study is expanded to consider the cooling flow physics under conditions without heat transfer. On the basis of these investigations, the paper shows a comparison between the flow with and without heat transfer. The results of the simulation with heat transfer show a negligible influence on the cooling flow temperature and a stronger influence on the material temperature. The results of the calculations are compared with measured data. The influence on the material temperature is verified with measured material temperatures from a Siemens Model V84.3A gas turbine prototype.
A Study on the Characteristics of a Vortex Type Two-Step Flow-Control Device
Authors: Cho Bong-Hyun , Bae Yoon-Yeong , Park Jong-Kyun
Published: February 2009

The effects of major flow path geometries on the flow characteristics of a Fluidic Device (FD) have been investigated experimentally and numerically. A full-scale FD has been designed and tested to verify the required characteristics, and the geometric effects are examined by changing the internal shape of the FD. As characteristics of the FD, time dependent flow rate, flow turndown and water level change are discussed. The flow turndown ratios are in the range of about 2 to 4, and they are highly depend on the exit nozzle diameter and the control port width, but almost not affected by the chamber height. As the flow turndown ratio increases, the water level in the pipe connected to the supply port becomes unstable, and it limits the flow turndown ratio, which is 2.5 in our case. The numerically predicted flow conditions in FD were highly dependent on the turbulence models, among them the RSM model gave the most reasonable results. In a high swirl case, the difference of flow rate between the test and the numerical simulation was about 10%. As the size of exit nozzle decreases, reverse flow in the cavity of the core increases and consequently the discharge flow rate reduces. In a low swirl case, the flow field in the chamber is extremely complicated and shows transient characteristic where the flow pattern in the core shows a large-scale oscillation.
Virtual Operation of Fluid Machinery by a Vortex Element Method
Authors: Ojima Akira , Kamemoto Kyoji
Published: February 2009

This paper describes recent works of practical applications of vortex element methods in the field of fluid machinery, carried by the authors’ group, explaining the mathematical basis of the method based on the Biot-Savart law. It is pointed as one of the most attractive features of the vortex method that the numerical simulation using the method is considered to be a new and simple technique of large eddy simulation, because they consist of simple algorithm based on physics of flow and it provides a completely grid-free Lagrangian calculation. As typical results of virtual operation of fluid machinery, the internal flow of a mixed-flow pump stage, unsteady flows through a wind turbine, and behaviors of submerged vortex in a pump sump are explained.
Gas Absorption, Aeration, by Fluidic Oscillator Operated by Gas-Liquid Two-Phase Flow
Authors: Shakouchi Toshihiko
Published: February 2009

It is known that a conventional feedback type and other type of fluidic oscillators can be operated not only by gas or liquid single phase flow but also by gas(air)-liquid(water) two-phase flow (Shakouchi, 1989, 2001). The two-phase jet flow oscillates periodically of the oscillator under some conditions, and then the gas, air bubble, and liquid flows are mixed and stirred forcibly. The contact area and time between gas and liquid flows increase considerably and then the much increasing of mass transfer, the diffusion or absorption of gas into liquid, will be expected. It may be able to construct an entirely new compact type gas-absorber, aerator, with a simple construction. In this paper, first the performance of fluidic oscillator operated by gas-liquid two-phase flow is made clear experimentally. Next, the aeration performance of the oscillator, namely the diffusion or absorption rate of air, dissolved oxygen, into water under various kind of operation conditions are examined experimentally. The following major results will be shown. (1) The oscillatory frequency f increases linearly with increasing the Re number (= udf/ν, u: mean velocity of water flow at the nozzle exit, df: nozzle width, ν: kinematic viscosity) and the void fraction α. (2) The pressure loss, flow resistance, Δp of the oscillator or increases rapidly with increasing Ref and linearly increasing α. (3) Dissolved oxygen in water can be increased considerably by fluidic oscillator operated by air-water two-phase flow, and it was well known that a new compact type aerator can be constructed by fluidic oscillator.
Flow Instability in Diverging-Flow Region With Flip-Flop Phenomenon Inside Diamond-Shaped Cylinder Bundles
Authors: Umeda S. , Taniguchi A. , Hasegawa S. , Yang Wen-Jei
Published: February 2009

An experimental study is performed to determine flow instability in the diverging-flow region with flip-flop phenomenon inside diamond-shaped cylinder bundles. Both two-dimensional particle imaging velocimetry (PIV) and two-dimensional laser Doppler velocimery (LDV) are employed to visualize and monitor flow phenomena. The study leads to the following disclosures in the diverging region with flip-flop phenomenon: (i) Velocity distribution can be expressed three-dimensionally and longitudinal vortices (migrating helically) appear in the secondary flow resulting from separation of the main stream. (ii) Power spectrum distribution with identical dominant frequency prevails in every row, indicating flow oscillations propagate over the entire passage. At the third row, the magnitude of power spectra reaches maximum near the “energy supply point” but subsequently diminishes to the minimum value at the apex of the succeeding cylinder where micro vortices alternately shedding on each of the downstream surface. (iii) The flow exhibits the characteristics of a jet tone.
Numerical Simulation of Flow Around a Simplified Car Body
Authors: Guilmineau Emmanuel
Published: February 2009

Simulations have been carried out for the generic car body (Ahmed body) for 25° and 35° slant angle. At a previous Workshop [1, 2], the results of different groups showed significant variations, even when the same turbulence models were used. This indicates that either the grids used in the investigation are too coarse to reduce the numerical errors below an acceptable limit, or that other factors, like boundary conditions, model implementation had a significant effect on the simulations. In any case, the results of the simulations were inconclusive, leading to a revaluation of this test case. In this study, we investigate numerically the flow around the Ahmed body for 25° and 35° slant angle. Results are compared with experimental data of Becker et al. [3].
Experiments on Fluid Mechanics in Flip-Chip Solder Connections
Authors: Wang Daijiao , Panton Ronald L.
Published: February 2009

This experimental research studies the formation of void bubbles within molten solder bumps in flip-chip connections. A theory based on thermocapillary flow reveals that the direction of heating influences void formation. Twelve chip-bump substrate assemblies were investigated using different heating profiles. A database on sizes and locations of voids in solder bumps was constructed. The observation on cases with melting direction from bottom to top supports the numerical study based on thermocapillary theory. The results show that a single big void is near the bump center with a few small voids near the edge when the melting direction is from bottom to top during solder reflow. When the melting direction was reversed, many small voids appear near the bottom edge with big voids in the middle of the bump. This experimental finding does not completely agree with the interpretation on the formation of voids by thermocapillary theory. However, the results do show that heat flux direction plays significant role in the formation and distribution of void bubbles in molten solder.
Experiments on Drop Impact and Coalescence at a Liquid/Liquid Interface
Authors: Mohamed-Kassim Zulfaa , Longmire Ellen K.
Published: February 2009

The gravity-driven impact and coalescence of a single drop through a liquid/liquid interface have been investigated experimentally. PIV images were obtained with a high frequency pulsed-laser and a high-speed video camera. Index-matching and a slight camera inclination were employed to eliminate optical distortion. The drop Reynolds numbers based on impact velocity and ambient viscosity were 20 and 68. During the approach towards the interface, viscous stresses generated a vortex ring inside each drop and a wake behind it. The subsequent deformation of the drop and the interface due to impact were observed to be more radical in the higher Re case. Both the wake shearing on the upper drop surface and interfacial deformation were significant in dissipating the vorticity inside the drops. After the vorticity dissipated, an outward flow developed along one radian between the ‘resting’ drop and the interface below generating a counter-rotating vortex pair. The eventual coalescence was typically off axis. During coalescence, a capillary ring wave propagated radially inward enhancing the collapse of the drop fluid into the bulk liquid below.
Interaction of a Single Large Wave With a Tall Fixed Structure: A Numerical Study
Authors: Ciobotaru Remus M. , Bidoae Razvan , Raad Peter E.
Published: February 2009

This paper presents a numerical study of the interaction of a single large wave with tall fixed structures in a rectangular channel. Three different shapes, a circle, a square and a rhombus, have been considered for the fixed structure. The numerical results are compared with experimental data available from experiments performed at the University of Washington, Seattle. The hydrodynamic force impinging on the vertical structure for different water impoundments behind the gate is considered and discussed. The motion of the fluid flow around the fixed structure is based on the solution of the complete Navier-Stokes equations. The free surface deformation is solved by the use of the Eulerian-Lagrangian Marker and Micro Cell (ELMMC) method.
Application of Number Density Transport Equation for the Recovery of Consistency in Multi-Field Model
Authors: Tomiyama Akio , Shimada Naoki , Asano Hiroyuki
Published: February 2009

It is demonstrated through a thought numerical experiment that a conventional two- or multi-fluid model suffers from an inconsistency problem, by which it would fail in accurately predicting two-phase dispersed flows even with reliable closure relations for interfacial transfer terms. To overcome the inconsistency, a numerical method based on a number density transport equation and a shape factor for a fluid or solid particle is proposed. The (N+2)-field model (NP2 model) proposed in our previous studies [1]–[3] is adopted as the basis of the proposed method. It is confirmed that the method gives better predictions than conventional multi-fluid models and recovers the consistency.
Direct Numerical Simulation of Gas-Particle Turbulent Swirling Flows in an Axially Rotating Pipe
Authors: Matsuzaki Kazuyoshi , Munekata Mizue , Ohba Hideki
Published: February 2009

The purpose of this study is to investigate the effect of the turbulent structure of the swirling flows on the particle motions using numerical simulation. In this work, we deal with the swirling turbulent flows in an axially rotating pipe because of focusing on the influence of swirl effect on the particle motions. Direct numerical simulation (DNS) of gas-particle turbulent swirling flows in the axially rotating pipe at the Reynolds number 180, based on the friction velocity and the pipe radius, and the rotating ratios 0.25 and 0.3 based on the bulk velocity was performed. Particle motions were treated by a Lagragian method with inter-particle collisions calculated by a deterministic method. In order to investigate the influence of swirl effect on the particle motions in detail, the one-way method in which fluid motion is not affected by particles is adopted. In particular, the effect of the inter-particle collisions on particle motions was carefully investigated because it is considered that particles accumulate near the wall due to the centrifugal force and local particle concentration is very high in the region.
Numerical Simulation of Ranque-Hilsch Effect
Authors: Hiroki Tsuyoshi , Hirata Eiji
Published: February 2009

Ranque-Hilsch effect, the phenomenon of total temperature separation, which occurs in swirling flows in a tube, was investigated numerically. URAN CFD simulations were performed to capture the unsteadiness, which was supposed to play an important role to produce the effect. The simulation produced total temperature separations, which are in fair agreement with the experimental values. No appreciable unsteadiness appeared in the simulations, presumably due to the fact that experimentally observed oscillations were resonance type. Attempts were made to produce oscillations by periodically varying the inlet velocity. But so far no resonance has been realized.
Experimental Study of a Rectangular Jet Impinging on a Circular Cylinder
Authors: Ishii Michiharu , Yang Xiao Feng , Matsubara Masaharu , Tsuchiya Yoshiaki , Yoshida Takashi
Published: February 2009

It was known that development of a jet from a rectangular orifice could be divided into three regions, which are 1) potential core region 2) characteristic decay region and 3) axisymmetric decay region. When a circular cylinder is placed in the rectangular jet, characteristic separation occurs around the cylinder and shapes of non-separation area on the cylinder are distinguished with the streamwise position of the cylinder. This flow geometry can be frequently seen in the industrial applications and drag and heat transfer of the cylinder would be important for the designs. In this study the rectangular jet impinging on a circular cylinder has been experimentally investigated. The relation between the jet development before impinging and separation area on the cylinder is especially focused. In the case that the cylinder is in the potential core region, the non-separation area distributes as saddle shape and the spanwise pressure distribution at the impinging line on the cylinder is almost constant around jet center and in the edge of jet impinging region it decreases with the distance. Then the pressure reaches at the minimum in the outside of the edge and recovers to the pressure of the circumference far from the edge. This pressure distribution suggests that flow just above the impinging line of cylinder blows toward the center and that the impinging flow is incredibly three-dimensional. When the cylinder is in the characteristic decay region, the non-separation area distributes as saddle shape as well as in the case of the potential core region. The spanwise impinging pressure distribution on the cylinder has maximums at the spanwise edges of impinging jet and sudden decrease out side of the jet. In this case the minima in the fringes of the jet were not observed. In the case of the axisymmetric region, the area of non-separation is elliptic and at the spanwise center the non-separated flow reaches backside of the cylinder.
Density Distribution Evaluation of Free Fall Particles Using CT and State Transition Matrix
Authors: Takei Masahiro , Ochi Mitsuaki , Saito Yoshifuru , Horii Kiyoshi
Published: February 2009

Spatial particle density distribution images in a pipe cross section have been evaluated by means of state transition matrix, which is a parameter indicating the dominant particle density transition patterns among time series images consisting of CT 2D-space and 1D-time. State transition characterizes the transition patterns for positions in a cross section as monotonous transitions, sudden transitions, and extreme value transitions. In free fall particles in a vertical pipe, high, sudden and extreme value transitions do not occur, because particle flow rate at this position is low, and therefore the probability of collision among particles is also low. A high, sudden and extreme value transitions occur near the pipe center when the particle flow rate is high, because the probability of collision among particles is high.
Proper Orthogonal Decomposition of Round Jet Turbulence Measured by Dynamic PIV
Authors: Bi W. , Sugii Y. , Okamoto K. , Madarame H.
Published: February 2009

In this study, we have used Dynamic PIV to measure the time-resolved turbulent velocity distributions of the near field flow of round jet turbulence. The Dynamic PIV system allows capturing particle images with kilohertz frame rate, mega-pixel resolution and gigabyte memory. We apply the system to study the spatial and temporal evolution of the coherent vortical structures in the near field of the round jet. 2-D and 3-D Proper Orthogonal Decomposition (POD) are employed to extract the coherent structures. The 3-D POD shows advantages over 2-D POD. The spatial distribution and temporal evolution of the flow structures extracted by 3-D POD are uncovered.
Three-Dimensional Reconstruction of Bubble Distribution in Two-Phase Flows With Metaball Technique
Authors: Furukawa Toru , Hassan Yassin A. , Ortiz-Villafuerte Javier
Published: February 2009

A three-dimensional reconstruction method using shadowgraphy for complex shaped bubbly flows is proposed. Bubble distribution is represented by a metaball object. Metaballs have the capability of representing smooth but complex surfaces. The fundamental strategy is searching the optimal metaball object equivalent to the original bubble distribution. The method does not assume that every bubble has a certain size or shape, therefore, intensive image processing on shadow images is not required. This method has applied to both synthetic bubble shadow images and those obtained from a real experiment, and the results indicate the potential ability of bubble reconstruction.
A Study on Resonance Impinging and Wall Jets
Authors: Shakouchi Toshihiko , Maruyama Takumi , Ando Toshitake , Tsujimoto Koichi , Watanabe Atsushi
Published: February 2009

Various kinds of impinging jets are used widely in many industry fields, such as the cooling of a heated plate or electronic components, drying of textiles, film, and paper because of their high heat and mass transfer rates at and near the stagnation point. Many studies on impinging jets from circular and orifice nozzles have been made [1]–[6]. It is well known that as nozzle-plate spacing decreases considerably the heat transfer rate becomes much larger, for example the maximum heat transfer rate of a circular impinging air jet with a low nozzle-plate spacing h/d = 0.1 (d: nozzle exit diameter) and Reynolds number Re = umd/ν = 2.3 × 104 is about 2.17 times of that for h/d = 0.2, but at the same time the flow resistance or operating power of the nozzle-plate system increases considerably. In order to improve or enhance the heat transfer rate, it is needed to increase the impinging mean and fluctuating velocities without increasing the operating power. To achieve this object it is considered to use a resonance jet. In this paper, the flow, acoustic and heat transfer characteristics of resonance free, impinging and wall jets are made clear experimentally. Moreover, flow visualization of the water jet flow by a tracer method is also made to examine the vortex structure at the shear layer and inside the resonance room. As a result, the heat transfer rate of the impinging jet by a resonance nozzle can be improved and enhanced considerably.
Dynamics of the Streamwise Vortices in an Axisymmetric Mixing Layer
Authors: Mori Hayato , Toyoda Kuniaki , Hiramoto Riho
Published: February 2009

The interaction of axisymmetric and streamwise vortices in the axisymmetric mixing layer developing along the jet boundary was investigated by a flow visualization technique. The jet was excited by axial and azimuthal perturbations to stabilize and enhance axisymmetric and streamwise vortices. A laser fluorescent dye and a laser light sheet were used to visualize the mixing layer. The three-dimensional views of the boundary surface of mixing layer were constructed by applying the Taylor hypothesis to the cross-sectional images. By the three-dimensional views, the interaction of axisymmetric and streamwise vortices was revealed, and the entrainment rate of the jet was also discussed in relation to the vortical structure.
Control of Turbulent Channel Flow Over a Backward-Facing Step by Suction
Authors: Sakuraba Kenichiro , Fukazawa Kazuharu , Sano Masatoshi
Published: February 2009

Experiments have been performed for a turbulent channel flow over a backward-facing step. The backward-facing step flow is actively controlled by equipping a slit at the bottom corner of the step and low momentum fluids in the recirculating region are sucked from the slit. The width of the slit is changed between 2, 3 and 5 mm, and suction flow ratio is varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient are measured behind the backward-facing step. In addition, the velocity profiles and turbulent intensities are measured by a split hot film probe. It is found that improvement in the heat transfer coefficient at the recirculating region and decreases in pressure loss are obtained by the suction. The heat transfer and pressure drop characteristics are controlled by the suction flow ratio, independently of suction velocities. When the suction flow ratio is 0.08, the highest performance is obtained.