bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on the New Micro-Bubble Generator and Its Application to Water Purification System
Authors: Fujiwara Akiko , Takagi Shu , Watanabe Kazuhiro , Matsumoto Yoichiro
Published: February 2009

Micro-bubble generation techniques are proposed in former investigations. In the present study one of the effective technique by using converging-diverging nozzle (venturi tube) is introduced. Rapid pressure recovery in the diverging nozzle induced bubble fission. The purpose of this study is to develop the new micro bubble generator, clarify the mechanism of the bubble fission in the venturi tube and elucidate the relation between the flow structure in the tube and the generated bubbles’ diameter. The developed micro generator has an advantage on the usage of wide range of void fraction. The observation by a high speed camera suggests that the bubble fission is caused by the strong shock-type pressure recovery in venturi tube. Finally in order to verify the applicability of micro-bubbles that generated by venturi tube to water purification system, floatation experiment was conducted. Bubble diameter in each condition is estimated by image processing technique respectively.
Numerical Analysis of Droplet Size Distribution Using Particle Method
Authors: Shibata K. , Koshizuka S. , Oka Y.
Published: February 2009

A continuous jet changes to droplets where jet breakup occurs. In this study, two-dimensional numerical analysis of jet breakup is performed using MPS method (Moving Particle Semi-implicit Method) which is a particle method for incompressible flows. The continuous fluid surrounding the jet is neglected. The size distribution of droplets is in agreement with the Nukiyama-Tanasawa distribution which has been widely used as an experimental correlation. Effects of the Weber number and the Froude number on the size distribution are also obtained from the calculation.
Balanced Force Implementation of the Continuum Surface Tension Force Method Into a Pressure Correction Algorithm
Authors: Francois Marianne M. , Kothe Douglas B. , Denby Edward D. , Sicilian James M. , Williams Matthew W.
Published: February 2009

A consistent formulation is presented for modeling surface tension driven flow with the continuum surface tension force (CSF) model within a volume of fluid (VOF) method using a pressure-correction projection method. We show that a flow algorithm whose inherent design is motivated by legislating force balance gives an exact (to round off) balance between surface tension forces and pressure gradients that arise as a result. This design eliminates one of the elusive impediments to more accurate CSF-based surface tension models, the remaining of which is curvature estimation accuracy. To validate our formulation, we present results for an equilibrium (static) drop in two and three dimensions having an arbitrary density ratio and demonstrate in the process that scaling effects within the CSF framework are insignificant.
Prediction of Stack Plume Downwash Using Computational Fluid Dynamics
Authors: Cain Stuart A. , Maroti Lewis A. , Lin Fangbiao
Published: February 2009

Accurate prediction of the fluid dynamic and thermodynamic characteristics of saturated buoyant plumes at power plant chimneys is important in developing reliable methods for controlling stack plume downwash. In particular, the accurate prediction and abatement of stack plume downwash is critical in northern climates where, under downwash conditions, the interaction of the saturated, warm plume with the cold outer chimney surface can lead to hazardous ice formation and buildup near the top of the chimney. When a stack is in downwash mode the plume leaving the stack turns downward and flows down along the leeward side of the shell. This is a direct consequence of the wind dynamic pressure acting on the plume and the low pressure in the wake of the shell. In downwash model it is not uncommon to see the plume travel down the shell one third to one half the chimney height and extend radially away from the shell a distance of twenty to thirty feet. This complex interaction of a turbulent thermally buoyant jet entering a cross wind has been studied extensively in the past both experimentally and theoretically with emphasis on the introduction of the jet through an orifice in an infinitely long flat plate. In the case of stack plume downwash the drag of the cylindrical stack in cross flow interacts with the plume under certain “worst-case” ambient wind conditions for the geographic location of the plant and draws the swirling plume into the wake region behind the stack. Once in this region, the distance the plume will travel down the leeward side of the chimney is a function of the ambient wind velocity and the plume velocity. Prediction of this complex, turbulent, three dimensional swirling flow including mixing of different temperature gases and the development of remedial devices to control, in particular, the problem of plume downwash has traditionally required an extensive and expensive wind tunnel model study. Results of these wind tunnel tests include empirical correlations and charts which have been used in the industry for decades. Advances in the capabilities of Computational Fluid Dynamics (CFD) have allowed engineers the ability to reliably study this flow phenomena in greater detail than attainable in a typical wind tunnel model study. In this paper Computational Fluid Dynamics (CFD) is used to predict downwash as a function of flue gas discharge velocity, wind velocity and temperature and the geometry of the stack near the discharge elevation. Further, two devices for minimizing plume downwash in a prototype stack installation are discussed and evaluated by the authors using CFD. Model validation simulations against experimental data and theoretical predictions of buoyant jets in cross flow are also presented and discussed.
A Numerical Simulation of Swirling Two-Phase Flow in BWR Steam-Water Separator and Its Optimization
Authors: Terasaka Haruo , Shimizu Sensuke , Kawahara Minoru
Published: February 2009

An advanced numerical method based on the two-fluid model has been developed. The solution method presented here is an extension of the SIMPLEST scheme, a fully implicit scheme for single-phase flow analysis. It is robust and unconditionally stable, and therefore it enables us to use a very large time step size. This feature is suitable for steady and/or slow transient flow analyses. Furthermore, it enhances numerical stability during rapid transient calculations. By using this method, swirling gas-liquid flow in a steam-water separator of Boiling Water Reactors (BWRs) was calculated and the hydrodynamics characteristics were investigated for optimization.
The Blockage Effects for the Unsteady Characteristics of the Near Wake Flows Behind a Bluff Body
Authors: Nakayama Hiroshi , Hirota Masafumi , Yamashita Hiroshi , Fukui Yoshio , Fujita Hideomi
Published: February 2009

Unsteady flow characteristics behind a triangular-shaped bluff body were experimentally investigated in a water flow of the Reynolds number range ReD = 500∼3000. The effect of changing the blockage ratio, BR, from BR = 0.2 to 0.6, was investigated. The experimental data of the velocity were obtained by using cinematic particle image velocimetry (PIV) to map the unsteady velocity field around the vortex-generating region. Based on the measured data, influences of the blockage on time-averaged velocities, turbulence intensity distributions and Strouhal number were examined. Moreover, proper orthogonal decomposition (POD) was performed on fluctuating vorticity fields to identify the most energetic parts of the vorticity fluctuations.
Study on Jet Flow Issuing From Pipe With Rotating Inclined Section
Authors: Nakashima Masahiro , Li Hui , Tabata Takahide , Nozaki Tsutomu
Published: February 2009

The water jet flow issuing from the rotating circular pipe with the inclined section has been studied by the method of the flow visualization and the image processing. The velocity distributions and the width of the jet have been measured in the cases of various inclined angles of the section and rotating speeds of the pipe. The effects of these variables on the jet diffusion have been clarified by measuring the jet width obtained from the superimposed images in the plane normal to the jet flow. As a result, it has been found that the jet diffusion is affected by the inclined angle and the rotating speed of the pipe. Furthermore, it has been clarified that there exists the rotating speed showing the effects of the rotating inclined section remarkably.
Measurement of Three Dimensional Position of Particles by Single CCD Image Including Lens Aberration
Authors: Ueki Hironobu , Ishida Masahiro , Sakaguchi Daisaku , Tokumoto Manabu
Published: February 2009

A new technique using a single CCD image through a lens system with large aberration is proposed in the present study for measurement of the three dimensional position of particles, in which a thick laser light source and a forward-scattering light from particles are processed. This optical system could be very compact and applicable to various flow measurements. The particle image detected by a CCD sensor is distorted in the present system due to lens aberrations. A transformation function of the optical system, which is the relationship between the reference particle with unit luminosity in the measuring volume and the corresponding distorted particle image detected by a CCD sensor through symmetric-convex lenses, is constructed theoretically based on the image formation optics of small particles. In order to obtain a high accuracy in the measurement, it is important to remove the background noise and the light intensity non-uniformity in the measuring volume from the CCD particle image by using a low-pass filtering technique based on the FFT analysis. By calculating the cross-correlation coefficient between the measured particle image and the data base images prepared by the above transformation function, the three dimensional position of the particle is determined as the position at which the largest cross-correlation coefficient is obtained. It is verified experimentally that this compact measuring system is useful for measurement of the three dimensional position of the particle with a good accuracy.
Active Flow Control of Wing Separated Flow
Authors: Ekaterinaris John A.
Published: February 2009

Numerical investigations of active flow control, which can offer significant improvements to wind–turbine rotor and turbomachinery performance by suppressing detrimental effects of separated flow, are presented. Simulations of pulsating jet flow control applied on wings at low speed, high Reynolds number turbulent flow and fixed angles of incidence are carried out. Efficient time–accurate numerical methods for the incompressible Navier–Stokes equations and advanced turbulence models are used for the prediction of the complex, unsteady flowfields. Pulsating jet active flow control is applied as a surface boundary condition and the flow is time-dependent. It is found that active flow control can enhance aerodynamic performance by reducing the adverse effects of separated flow. The effect of the jet location, pulsation frequency, and jet exit velocity on flow control is investigated.
A Novel Technique for Analyzing Hydraulic Transients by Method of Characteristics
Authors: Pu Jianing
Published: February 2009

In analyzing hydraulic transients in complex pipeline systems by method of characteristics, existing approaches can not be fully satisfactory regard to numerical accuracy, computation speed, and application flexibility and simplicity. Trying to overcome this shortcomings, the paper puts forward a novel technique: in node computations, variable time steps are used, the common for boundaries and the different for lines; in every computation cycle, analyses of boundary nodes are always prior to that of interior ones, while simulation times of interior nodes are always prior to that of boundary ones; in solution of boundaries, only interpolation is used. Explanations and numerical experiments demonstrate its usage flexibility and simplicity, simulation accuracy, and executing time saving. It is specially suitable to analyses of complex systems.
Studies on Techniques and Devices of Controlling Surge in Pipelines
Authors: Zhang Weiming , Li Xudong , Pu Jianing , Yong Qiwei
Published: February 2009

Water hammer in pipelines may cause serious accident. To solve the problem, three mechanical devices — rubber tube relief valve, metal plug relief valve and pressure-surge-proof valve actuator are developed. The first two devices are for controlling the surge after water hammer occurs, the last one is for preventing it from occurring at valve. When the monitored pressure increases at a rate higher than the setting rate, or the pressure reaches the setting maximum value, the relieve valve will release liquid to constrain strong surge from water hammer. The key part of one relieve valve is a rubber tube; the other is metal valve plug. Both of the relief valves could also be used as common relief valves. The pressure-surge-proof valve actuator works on the principle of damping the movement of the valve stem at the closing end of its travel. The key part is a two-stage-damping device, which is installed onto a valve actuator. When the valve stem goes into the last part of full travel the device provide damping action in two stages to weaken the surge from valve opening or closing.
Research on Waterhammer Caused by a Rapid Gas Production in an LWR Severe Accident: 2 — 2D Analysis With RELAP5-3D
Authors: Adachi Masaki , Inasaka Fujio , Shiozaki Koki , Aya Izuo
Published: February 2009

Water hammer load induced by ex-vessel steam explosion, which is resulted from molten fuel in water pool, still includes many uncertain factors in safety research against severe accident for design criteria of next generation nuclear power plant. One of the factors is degree of coherency in water bulk accelerated by the explosion. If high-coherent movement in many pieces of water bulk in the pool (as many pieces of the bulk move with coincidence and same direction), an excessive load will be applied to inner structure of the plant. To evaluate the factor, 2 dimensional analysis to simulate the coherent movement induced by pressurized air injection in containment vessel, has been examined with RELAP5-3D, which is one of the most popular codes in nuclear engineering. This 2D analysis simulated glowing single component zone of pressurized air, regarded as large bubble, and cloud-like interface around the zone observed in the experiment where momentum is transferred from the air to the water. This analysis also predicted virtually uniform acceleration of the bulk and detailed 2D flow proceeded to air penetration through the water. And water hammer pressure could also be simulated, with evaluating sonic speed drop through two-component mixed layer around the bulk.
An Unstructured RANS Study of Tip-Leakage Vortex Cavitation Inception
Authors: Brewer W. H. , Marcum D. L. , Jessup S. D. , Chesnakas C. , Hyams D. G. , Sreenivas K.
Published: February 2009

To study the physics of cavitation inception, a ducted propulsor simulation is developed and extensively validated with experimental results. The numerical method is shown to be in good agreement with experimental measurements made in the vortex. The simulation is used as a tool for investigating the minimum pressure, circulation, and axial/tangential velocities in the vortex core. Additionally, the tool is used to study Reynolds number scaling effects of cavitation inception. The simulation reveals that the leakage vortex exhibits little dependence on Reynolds number, while the trailing edge vortex appears to exhibit classical trends. Moreover, the trailing edge, albeit the weaker vortex, appears to be causing inception.
Non-Linear Two-Equation Model Taking Into Account the Wall-Limiting Behaviour and Redistribution of Stress Components
Authors: Hattori Hirofumi , Nagano Yasutaka
Published: February 2009

Nonlinear k–ε models have been extensively used in technological applications. It is clear from the assessment of the existing nonlinear k–ε models using DNS databases that the nonlinear models can not satisfy and reproduce exactly the wall-limiting behaviour and the anisotropy of Reynolds normal stress components. Especially, the Reynolds normal stress component, u22, in the wall-normal direction, which is proportional to x24 near the wall is not satisfied. Since the wall limiting behaviour of Reynolds normal stress components in the nonlinear model is determined by the turbulence energy k, which is proportional to x22 in the model, the Reynolds stress components, u12, u22 and u32 are proportional to x22. In this study, we have proposed a new nonlinear k–ε model which satisfies exactly the wall limiting behaviour of Reynolds normal stress components in the inertial and the noninertial frames. The proposed model can also predict well the anisotropy of the Reynolds normal stress components near the wall.
Large Eddy Simulation of Lifted Non-Premixed Jet Flames Using 2-Scalar Flamelet Model
Authors: Hirohata Mikikane , Taniguchi Nobuyuki , Kobayashi Toshio
Published: February 2009

In this paper we introduce the LES of lifted non-premixed jet flames based on two-scalar flamelet modeling. The flamelet G-equation for premixed combustion and the conserved scalar equation for non-premixed combustion are combined to express partially premixed flame propagation. In order to close filtered G-equation, the subgrid burning velocity model is proposed based on the concept that small triple flamelet are projected into unburnt gas from the flame-base of the lifted non-premixed flame. The calculation results are shown that wrinkling lifted flames are simulated and the difference of the lift-off height and the flame-shape with the variation of the co-flowing velocity is predicted. It is also confirmed that the conditional axial velocity near the flame base which is thought to relate the condition of the flame stabilization is on the order of two–three times of the laminar burning velocity, which agrees well with the experimental data. We hope that this method will be useful to investigate the flame stabilizing mechanism or flame controls of practical non-premixed jet flames.
Measurement of Bubbly Flow in a Vertical Pipe Using Ultrasonic Doppler Method
Authors: Murakawa Hideki , Kikura Hiroshige , Aritomi Masanori , Mori Michitsugu
Published: February 2009

In order to clarify the microscopic flow structure, the ultrasonic Doppler method was applied to the measurement of two-phase bubbly flow in vertical pipe (i.d.50mm). Liquid flow structure might strongly be influenced by the characteristic of the injected bubbles, i.e. bubbles’ size and void fraction. In this study, a bubble generator was newly designed with the purpose to control the bubble size and void fraction, independent of liquid main-flow rate. The experiment was performed at z/d = 66 from the bubble generator. Liquid flow rates were of the Reynolds numbers ranging from Rem = 3700 to 6200. The gas flow rate was constant at JG = 0.00348(m/s) at the measurement position. By analyzing the bubbles’ picture, it was confirmed that bubble size distribution and average bubble size were almost constant if the liquid flow rate were changed. The ultrasonic Doppler method has the capability of measuring the instantaneous velocity profiles of both phases at the same time. By processing the data based on pattern recognition, the recorded data can be classified to several groups. Using this method, the authors have tried to measure the bubbly flow in rectangular channel. In the present study, the application of this method to bubbly flow in circular pipe was satisfactory to obtain the liquid velocity distribution in bubbly flow and surrounding bubbles. From these results, it was clarified that velocity profile in bubbly flow in circular pipe has a maximum value near the pipe wall. Furthermore, velocity profiles around the bubble are influenced by leading bubbles.
An Improved Three-Dimensional Level Set Method for Gas-Liquid Two-Phase Flows (Keynote)
Authors: Takahira Hiroyuki , Horiuchi Tomonori , Banerjee Sanjoy
Published: February 2009

For the present study, we developed a three-dimensional numerical method based on the level set method that is applicable to two-phase systems with high-density ratio. The present solver for the Navier-Stokes equations was based on the projection method with a non-staggered grid. We improved the treatment of the convection terms and the interpolation method that was used to obtain the intermediate volume flux defined on the cell faces. We also improved the solver for the pressure Poisson equations and the reinitialization procedure of the level set function. It was shown that the present solver worked very well even for a density ratio of the two fluids of 1:1000. We simulated the coalescence of two rising bubbles under gravity, and a gas bubble bursting at a free surface to evaluate mass conservation for the present method. It was also shown that the volume conservation (i.e., mass conservation) of bubbles was very good even after bubble coalescence.
Investigation of Air Entrainment: A Numerical Approach
Authors: Kshirsagar J. T. , Joshi S. G.
Published: February 2009

The air entrainment in sumps (Pump Intake) is a commonly observed phenomenon at low water level and high Froude number corresponding to flow rates higher than the rated flow. The air entrainment initiates with the formation of small vortex like structure on the surface with its position varying in the vicinity of Pump intake portion. Normally it calls for two-phase flow analysis (and possibly transient also) to correctly predict the air entrainment phenomenon using computational fluid dynamics approach. We at CRED, Kirloskar Brothers Limited could predict the root cause for air entrainment by studying the vortex formation well within the flow. A single-phase steady state flow was analyzed. Two test cases were studied. IOWA University had published a sump case with results from computational fluid dynamics studies. The other case was the actual sump model study carried out using experimental setup wherein the air entrainment was observed. The paper presents the comparison of the predictions with results from these two test cases.
A Glance Back and Outlook of Computational Fluid Dynamics (Keynote Paper)
Authors: Shang J. S.
Published: February 2009

The development of computational fluid dynamics (CFD) can be traced back as far as the early 1900’s. The pioneering efforts by Richardson [1], Courant, Friedrichs, and Lewy [2], Southwell [3], Von Neumann [4], Lax [5], as well as Godunov [6] address the fundamental issues in numerical analyses for CFD. It is immediately clear that a major portion of these efforts was focused on one of the most difficult problems in resolving the discontinuous fluid phenomena in a discretized space — the Riemann problem [7]. As it will be seen later, it remains the most studied problem in CFD. However, if one is interested in the viscous flow simulation, Thom [8] probably obtained the first-ever numerical solution by solving the partial differential equation for a low speed flow past a circular cylinder. For a scholarly description of the CFD historical perspective, the books by Roach [9] and Tannehill, Anderson, and Pletcher [10] are highly recommended.
Remote Site Access to a Turbomachinery Lab for Education and Research (Keynote Paper)
Authors: Williams David R.
Published: February 2009

An axial flow compressor has been designed to allow control and data acquisition from remote site locations. The design of the controller builds upon the experiences of other universities with remote access laboratories. The compressor hardware and data acquisition system are accessible via a LabVIEW interface. The long term objective of the project is to make turbomachinery experiments available to anyone with an interest in the subject and an Internet connection.
A Numerical Simulation of an Air Conditioning System in Office Using Weak Airflow
Authors: Shimizu Sensuke , Terasaka Haruo , Yamada Akira
Published: February 2009

The objective in this study is to evaluate thermal environment of a room with an advanced ceiling hidden type air-conditioner using numerical simulation. As the characteristic of the air-conditioner, it supplies a weak airflow from a large inlet to a room. Circulator fans are fixed on the ceiling. Numerical simulation is performed to a room with the air-conditioner. PMV [1] is calculated from the obtained data and thermal sensation of the people is investigated. From the PMV distribution, it was found that this sensation was improved by the advanced air-conditioner.
Parallel Finite Element Analysis of Flow and Heat Transfer on PC-Cluster
Authors: Shirazaki Minoru , Himeno Ryutaro
Published: February 2009

In this paper, numerical simulations of a coupling phenomenon including flow of thermal fluid and heat transfer in a solid are performed on a PC-cluster. To simulate the coupling phenomenon, the flow and the heat transfer in solid are computed simultaneously by solving the same governing equations in which the flow velocity in the solid region is set to zero. By using this method, good parallel efficiency is obtained on PC-Clusters. Some problems, which are cooling of a large-scale integration (LSI) package, flow around a heated candlestick and the internal and external flows of two tubes with consideration of heat transfer, are solved. It is confirmed that the coupling phenomenon of flow and heat transfer can be treated easily using this approach on a parallel environment.
The Asymptotic Temperature Profile for Forced Convection Turbulent Boundary Layers With and Without Pressure Gradient
Authors: Wang Xia , Castillo Luciano
Published: February 2009

Similarity analysis of the equations of motion is used in order to study forced convection turbulent boundary layers with and without pressure gradient. New scalings are found for both the inner and the outer temperature profiles, respectively. It is shown that by normalizing the temperature profiles using the new scalings, the effects from the Pe´clet number and pressure gradient can be removed completely from the profiles. Therefore, the asymptotic solutions can be obtained even at the finite Pe´clet number. Moreover, using the Near-Asymptotic principle, a power law solution is derived for the temperature profile in the overlap region. This power law solution is a consequence of the fact that the boundary layer depends on two different temperature scalings.
Improvement of Centrifugal Fan on Noise With Inducer
Authors: Hayashi Hidechito , Kodama Yoshio , Ogino Kazuo
Published: February 2009

We improved the centrifugal fan for the noise and fluid performance. The fan has the inducer that is unified to the main blade. The geometry of the inducer was obtained with the tuft method and is unique. The fluid turns from axis- to radial-direction in the inducer. The inlet angle and the chord length of the inducer vary in span position. The aerodynamic and noise characteristics of the impeller with inducer have been compared to one without inducer. The total pressure and the efficiency of the impeller with inducer are increased about 20% and 5% in all flow rate. Because the pressure rise occurs in the inducer. And the pressure loss at the inlet of the blade becomes very small. The influence of the leakage flow between the shroud and the bellmouth is restricted near the front shroud, and then the separation of the boundary layer is controlled. The wake width of the main blade becomes fairly small. The specific noise level, which presents the noise performance of the fan, can be reduced about 2–4dB in wide flow rate.
Prediction Calculation of the Cavitation Erosion Generated in Connection With a High-Pressure Jet
Authors: Yuge Atsushi , Takeno Ichiro , Takaishi Tatsuo , Matsumoto Yoichiro
Published: February 2009

High-pressure jets are being pursued in diesel engines in order to facilitate development of next-generation fuel injection systems aiming at high performance, high fuel economy, and low emissions of smoke. Cavitation erosion accompanying the use of high-pressure jets for diesel fuel injection pumps is a factor responsible for reduced equipment durability and performance. In response, the project reported here involved the production of test equipment for the purpose of replicating the behavior of a fuel injection pump as it would occur in an actual diesel engine, with erosion testing, and analysis of the shock pressure by the cavitation, and its generating part. As a result, the following behaviors were noted. (1) In the 3-dimensional analysis of an unsteady cavitation jet stream, the shock pressure by the cavitation and its generating part can be predicted. (2) If the exit clearance of a hole is adjusted, the generating position of a erosion is controllable.
Boundary Layer Dispersion of Near-Wall Injected Particles of Various Inertias
Authors: Dorgan Andrew J. , Loth Eric , Bocksell Todd L. , Yeung P. K.
Published: February 2009

A direct numerical simulation approach was employed along with a Lagrangian particle tracking technique to investigate particle motion and dispersion in a turbulent boundary layer. The present study investigated a range of particle inertias corresponding to outer Stokes numbers varying from 10−4 to 1. In all cases, the ratio of particle terminal velocity to fluid friction velocity was held constant at 10−2 such that the effects of particle inertia would be isolated and dominant with respect to particle dispersion. The particles were injected near the wall at a height of four wall units (with elastic wall collision specified at one wall unit) and their locations recorded at several streamwise planes. Particles having an outer Stokes number much less than unity reach a similar outer flow distribution profile by the time they pass a collection plane located at eight boundary layer thicknesses downstream of injection. Moderately larger particles tended to yield increased wall collisions and increased near-wall concentrations. The increased concentration in the near-wall region (or reduced diffusion away from the wall) is attributed to a coupling of inertia effects and turbulent structures for the non-homogeneous flow (sometimes referred to as turbophoresis). The highest Stokes number particles yield the highest near-wall concentration, but resulted in a decrease in wall collisions in the first few collision bins as it tends to be unaffected by the near-wall structures.
Optimal Pump Elevation and Configuration for Mixing Erosion-Resisting Radioactive Tank Waste
Authors: Onishi Yasuo , Trent Donald S. , Yokuda Satoru T. , Hier Majumder Catherine A. , Martinen Edgar W. , Rieck Curt A.
Published: February 2009

At the U.S. Department of Energy’s Hanford Site, 300-hp mixer pumps will be installed in the 4,000-m3 double-shell tanks (DSTs) to stir the radioactive sludge and supernatant liquid waste so that it can be retrieved for subsequent treatment and disposal. A baseline mixer pump that has been used in the DSTs has an intake at the bottom and two injection nozzles at the top. The pump is placed approximately 0.46 m above the bottom of the tank. We compared the predicted mixing performance of this baseline pump with an alternative pump—an inverted pump with the inlet at the top and injection nozzles at the bottom. Model predictions were compared with some measured data. We evaluated 16 cases of baseline and inverted pump conditions with mixer pumps situated at levels ranging from right on the tank bottom to 0.83 m above the tank bottom. Model results generally indicated sludge erosion is greater the closer the pump’s injection nozzle is to the tank bottom. These results provided an evaluation of mixing performance for use in a cost, risk, and benefit analysis to determine which pump configuration should be used for DST waste retrieval activities.
Effects of Cantilever Aspect Ratio and Liquid-Solid Suspensions on Resonance in a Confined Cavity
Authors: Naik Tikeswar , Longmire Ellen K. , Mantell Susan C.
Published: February 2009

The dynamic response of millimeter-scale cantilevers was investigated in liquid-solid suspensions. The gap height d between the cantilever and a solid surface was varied from millimeter range to micrometer range. Different Bimorph cantilevers (aspect ratio b/h = 2.0–12.1, where b is the cantilever width and h is the cantilever thickness) were examined. The added mass coefficient increased linearly with aspect ratio. The normalized viscous damping coefficient increased with increasing kinetic Reynolds number but appeared independent of the cantilever aspect ratio. Cantilevers oscillating in liquid-solid suspensions experienced higher effective viscosity than that predicted by shear flow type models. The damping caused by a suspension containing 2% glass beads by volume was significantly stronger than that in a pure liquid for dimensionless particle diameters Dp/d ≥ 0.02.
Flow Over Model Buildings With Sloped Roofs
Authors: Poitras Ge´rard J. , Brizzi Laurent-E. , Gagnon Yves
Published: February 2009

The flow field around model buildings with different sloped roofs was investigated using Particle Image Velocimetry (PIV). The flow around model buildings having flat roofs was studied by many authors. Although buildings with sloped roofs are the most common type of low rise buildings, the flow around these buildings are not well known. Most of the studies for these types of buildings were made for the determination of surface pressures. The aim of this study is to highlight the fundamental differences between flat roofs and sloped roofs for three-dimensional obstacle flows. The experiments were performed in a wind tunnel having a cross section of 300 mm × 400 mm. All the models were 30 mm high (vertical wall) and were placed in a thin turbulent boundary layer. Three Reynolds numbers, based on the height of the obstacle, were used (12000, 22 000, 32 000). Furthermore, the quantitative data is analyzed and statistical results describing the mean and fluctuating velocity fields are presented. Finally, the surface pressures on the median plane were studied in order to correlate these pressures with the flow topology of different sloped roofs. It was found that upstream of the obstacle, the flow topology for the model having sloped roofs was similar to that of a flat roof apart from an increase in size of the well-known horseshoe vortex. However, the flow topology is not the same over different roofs, on the sides of the models and immediately downstream of the models. For the Reynolds number studied, there are no coherent flow structures over the upstream sloped roofs while an arch vortex is created on the sides of the models. This arch vortex is similar to the arch vortex that is created over a flat roof. An arch vortex is also present downstream of the models. The lower part of this vortex is similar to the one created for a flat roof. However, the upper part of the arch vortex starts from the tip of the roof and continues downstream and has an ellipse shape. This vortex also increases in size with the slope of the roof.
Secondary Pressure Correction to Improve the SIMPLE Method
Authors: Zhang Sijun , Zhao Xiang
Published: February 2009

The SIMPLE method and its various modified versions have been widely used over the past two decades in the fluid flow modeling. One important feature in these SIMPLE-like algorithms is the use of a pressure correction in the pressure-correction equation, which is known to be effective in correcting the velocity field but not so in correcting the pressure field. This paper presents a modified SIMPLE algorithm to overcome this problem. This modified SIMPLE method, while still using the pressure correction for correcting the velocity field like the SIMPLE method, introduces a secondary pressure correction for correcting the pressure field. Numerical calculations of gas-solid flow in a fluidized bed suggest that this method can accelerate convergence, improve accuracy and save CPU time, compared to the SIMPLE method.
Basic Boundary Conditions for Incompressible and Compressible Flows Using Unstructured Meshes
Authors: Basara Branislav
Published: February 2009

The paper compiles the basic and frequently used boundary conditions in CFD calculations. Regardless of the type of boundary conditions, Dirichlet or Neumman, there are very important differences in the implementation procedure depending on the solved equations as well as on variables which are updated on the boundaries. Boundary conditions in the frame of the control volume method presented here, are adopted for the unstructured grids consisting of arbitrary polyhedral cells. There are no limitations on the employment of boundary conditions regarding mesh type. Some special treatments to improve results and the convergence rate are proposed. The emphasis is on the wall and the pressure boundaries.
Estimation of Interfacial Area Concentration for Two-Phase Slug Flow From Dual-Probe Hot-Film Measurements
Authors: Wang G. , Ching C. Y.
Published: February 2009

A relatively simple technique has been developed to estimate the interfacial area concentration (ai) of vertically upward gas-liquid slug flow from dual-probe hot-film anemometry measurements. The slug flow is modeled as a series of Taylor bubbles having a regular bullet-like shape separated by liquid slugs containing small spherical gas bubbles. The total interfacial area is the sum of the Taylor bubble surface area and the surface area of the bubbles in the liquid slugs. The ai is estimated from the mean diameter and local void fraction of the bubbles in the liquid slugs, and the length of the Taylor bubbles. These parameters are obtained through selective discrimination of the hot-film signals to separate the Taylor bubbles from the smaller gas bubbles in the liquid slugs. The important non-dimensional parameters that influence the interfacial area concentration are obtained using the synthesis method. A new correlation for ai for vertically-upward slug flow is developed based on the present measurements.
Oil-Water Separation in a Novel Liquid-Liquid Cylindrical Cyclone (LLCC) Compact Separator: Experiments and Modeling
Authors: Oropeza-Vazquez C. , Afanador E. , Gomez L. , Wang S. , Mohan R. , Shoham O. , Kouba G.
Published: February 2009

The hydrodynamics of multiphase flow in a Liquid-Liquid Cylindrical Cyclone (LLCC) compact separator have been studied experimentally and theoretically for evaluation of its performance as a free water knockout device. In the LLCC, no complete oil-water separation occurs. Rather, it performs as a free water knockout, delivering a clean water stream in the underflow and an oil rich stream in the overflow. A total of 260 runs have been conducted for the LLCC for water-dominated flow conditions. Four different flow patterns in the inlet have been identified, namely, Stratified flow, Oil-in-Water Dispersion and Water Layer flow, Double Oil-in-Water Dispersion flow, and Oil-in-Water Dispersion flow. For all runs, an optimal split ratio (underflow to inlet flow rate ratio) exists, where the flow rate in the water stream is maximum with 100% water cut. The value of the optimal split ratio depends upon the existing inlet flow pattern, varying between 60% (for Stratified and Oil-in-Water Dispersion and Water Layer flow patterns) to 20% for the other inlet flow patterns. For split ratios higher than the optimal one, the water cut in the underflow stream decreases as the split ratio increases. A novel mechanistic model has been developed for the prediction of the complex flow behavior and the separation efficiency in the LLCC. The model consists of several sub-models, including inlet analysis, nozzle analysis, droplet size distribution model, and separation model based on droplet trajectories in swirling flow. Comparisons between the experimental data and the LLCC model predictions show excellent agreement. The model is capable of predicting both the trend of the experimental data as well as the absolute measured values. The developed model can be utilized for the design and performance analysis of the LLCC.
Aerobreakup in Rarefied Supersonic Gas Flows (Keynote)
Authors: Theofanous T. G. , Li G. J. , Dinh T. N.
Published: February 2009

We present new experimental results on the interfacial instabilities and breakup of Newtonian liquid drops suddenly exposed to rarefied, high-speed (Mach 3) air flows. The experimental approach allows for the first time detailed observation of interfacial phenomena and mixing throughout the breakup cycle over a wide range of Weber numbers. Key findings are that Rayleigh-Taylor instability alone is the active mechanism for free stream Weber numbers as low as 28 for low viscosity liquids and that stripping rather than piercing is the asymptotic regime as We→∞. This and other detailed visual evidence over 26 < We < 2600 are uniquely suitable for testing CFD simulations on the way to basic understanding of aerobreakup over a broad range of conditions.
Characteristics of Air-Oil Two-Phase Flow Across a Sudden Expansion
Authors: Ahmed W. H. , Ching C. Y. , Shoukri M.
Published: February 2009

The pressure recovery and void fraction change of air-oil two-phase flow across a sudden expansion has been investigated experimentally over a range of flow conditions. The pressure upstream and downstream of a half-inch to one-inch sudden expansion was measured using a series of pressure taps, and capacitance sensors were used to measure the void fraction along the test section. The void fraction increases as the flow approaches the sudden expansion section, with a sudden increase immediately downstream of the expansion followed by a gradual relaxation to the fully developed value further downstream. The normalized pressure recovery coefficient using the dynamic head based on the homogeneous density and two-phase velocity is found to collapse when plotted as a function of the mass quality. The experimental pressure recovery data are compared with predictions from existing models, and are found to be in good agreement with the Delhaye model with the void fraction relation of Wallis.
A Study on Flow in Duct Constructed of Nonwoven Fabric
Authors: Sakamoto Masahiko , Sawabe Toshiyuki , Izumi Kiichiro
Published: February 2009

The purpose of this paper is to investigate both the flow characteristics in the sock type of the air filter constructed of nonwoven fabric and the effect on drag reduction in a circular pipe flow by means of the wall coated with nonwoven fabric. The nonwoven fabric used in these experiments is an electret one made of polypropylene, and the fiber distribution is a random laying. The fiber is about 4 μ m in diameter and 0.6 mm in thickness of web. The nonwoven fabric without adhesion of dust was used in these experiments. The pressure distribution along the flow direction was measured for various parameters such as Reynolds number, shape of the air filter, and type of nonwoven fabric. The value of the permeability for the present nonwoven fabric is on the order of 10−11(m2) within the limits of this experiment. The pressure in the sock type of the air filter increases with increasing Re. The experimental results can be explained by Darcy’s law as d/L is larger than 0.1. In the small range of Re the calculated values obtained by the one-dimensional flow model qualitatively agree with those obtained by this experiment. It was proven that the wall coated with the nonwoven fabric is effective to reduce the drag in the circular pipe flow.
Flowmetering of Shear-Thinning Non-Newtonian Liquids (Keynote)
Authors: Owen I. , Fyrippi I. , Escudier M. P.
Published: February 2009

This paper describes the results of an investigation into the performance of Coriolis, Electromagnetic, and clamp-on single-beam Ultrasonic flowmeters operating with non-Newtonian liquids. The flowmeters have been tested on Newtonian liquids (water and a glycerine/water solution) and non-Newtonian liquids (various polymer solutions and a synthetic clay) with flow rates that span the laminar and turbulent regions. It has been shown that the Coriolis flowmeter operates within the manufacturer’s specification with non-Newtonian liquids. The Electromagnetic flowmeter showed a slight deviation during transition, typically 1%. The Ultrasonic flowmeter showed very significant deviations during transition, typically 15%. It has been clearly demonstrated that flowmeters which are sensitive to flow velocity profile are particularly unsuitable for use with non-Newtonian liquids. Not only do non-Newtonian liquids have different flow velocity profiles to Newtonian liquids, they also have different criteria for laminar/turbulent transition.
LDV and PIV Velocity Results in a Thermosiphon
Authors: Kulman J. , Gray D. , Sivanagere S. , Guffey S.
Published: February 2009

Heat transfer and flow characteristics have been determined for a single-phase rectangular loop thermosiphon. The plane of the loop was vertical, and tests were performed with in-plane tilt angles ranging from 3.6° CW to 4.2° CCW. Velocity profiles were measured in one vertical leg of the loop using both a single-component Laser Doppler Velocimeter (LDV), and a commercial Particle Image Velocimeter (PIV) system. The LDV data and PIV data were found to be in good agreement. The measured average velocities were approximately 2–2.5 cm/s at an average heating rate of 70 W, and were independent of tilt angle. Significant RMS fluctuations of 10–20% of the mean velocity were observed in the test section, in spite of the laminar or transitional Reynolds numbers (order of 700, based on the hydraulic diameter). These fluctuations have been attributed to vortex shedding from the upstream temperature probes and mitre bends, rather than to fully developed turbulence. Animations of the PIV data clearly show these large scale unsteady flow patterns. Multiple steady state flow patterns were not observed.
Flow Simulation Around a Rotating Circular Cylinder With Surface Roughness by the Vortex Method
Authors: Tsukiji Tetsuhiro , Matsubara Yuko
Published: February 2009

The two-dimensional flow around a rotating circular cylinder with surface roughness in a steady uniform flow is investigated using a vortex method. The Reynolds number is 9500, while the rotating speed ratios of the peripheral velocity to the uniform velocity is 0–1.0. The surface roughness is distributed around the circular cylinder and its strength is 0.5% of the diameter. The viscous diffusion effects and the no-slip condition are considered. Before the calculation for a rotating circular cylinder with the surface roughness, the flow simulation for a circular cylinder in the steady uniform flow was conducted to confirm the present method. The development of the twin vortices and the velocity profiles behind the circular cylinder at the beginning of the calculation are compared with the previous experimental results. It is found that the calculated results are in good agreement with the experiments. The development of the vortices, the drag and the lift coefficients are computed by changing the rotating speed ratio for the circular cylinder both with the surface roughness and without it. The influence of the surface roughness and the rotating speed ratio on the vortex development, the drag and the lift coefficients are examined.