bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermittent Noises Due to Bubbles Sucked Into a Siphon Pipe
Authors: Shigefuji Hiroshi , Mochizuki Osamu
Published: February 2009

Intermittent noises arising from a siphon pipe attached to a toilet bowl are investigated experimentally. The see-through model of a drained system is used to study the relation between noises and flow patterns near the entrance of the siphon pipe. We observed the different manner of the formation of large bubbles for different values of sucking velocity in the siphon pipe. The overall value of the noise in the sucking period increases with increasing the draining velocity. When the draining velocity is constant, the largest noise is generated at completion of the large bubble attached on the wall. The intermittent noises in the early stage of the period are found to be caused by small bubbles separated from the tail of the large bubble. The small bubbles are torn off because of shear stress of the main flow acting on the bubble surface. Another intermittent noises arising in the last stage is caused by periodic formation of the large bubble near the entrance. The detailed process of the bubble formation in the siphon pipe and the noises are discussed in this paper.
Prediction of Aerodynamic Noise Radiated From a Vertical-Axis Wind Turbine
Authors: Iida Akiyoshi , Mizuno Akisato , Kamemoto Kyoji
Published: February 2009

Unsteady flow field and flow induced noise of vertical axis wind turbine are numerically investigated. The flow field is numerically calculated by the vortex method with core-spreading model. This simulation obtains aerodynamic performance and aerodynamic forces. Aerodynamic noise is also simulated by using Ffowcs Williams-Hawkings equation with compact body and low-Mach number assumptions. Tip speed of rotor blades are not so high, then the contribution of the moving sound source is smaller than that of the dipole sound source. Since the maximum power coefficient of VAWT can be obtained at lower tip-speed ratio compared to the conventional, horizontal axis wind turbines, the aerodynamic noise from vertical axis wind turbine is smaller than that of the conventional wind turbines at the same aerodynamic performance. This result indicates that the vertical axis wind turbines are useful to develop low-noise wind turbines.
Numerical Simulation of a Self-Stabilizing Rotor of a Centrifugal Pump
Authors: Steinbrecher Christian , Skoda Romuald , Schilling Rudolf , Mu¨ller Norbert , Breitenbach Alexander , Mendler Nikolaus
Published: February 2009

The goal of this investigation is to contribute to the design of a centrifugal pump that can operate without bearings. This paper presents numerical studies of fluid-structure interactions on a rotating disc that can move axially unrestricted in a housing. This model mimics the gap flow between the rotor and the housing of a centrifugal pump, which stabilizes the rotor. Fluid-structure occur because of hydrodynamic forces that displace the rotor. First the effect responsible for stabilizing the rotor is described in detail. The next section presents the employed 3D Navier-Stokes Computational Fluid Dynamics (CFD) code. Special interest is given to a correct implementation of the Space-Conservation Law, where the time-dependent simulations use moving meshes. The code includes additional modules for grid generation and for calculation of the hydrodynamic forces acting on the rotor surfaces and the resulting displacement of the entire rotor. Newton’s second law is used for the coupling between hydrodynamic forces and resulting axial displacement. Results from stationary simulations are presented and compared with measurements, from the German Heart Center Munich, that show an axial displacement of the rotor results in a hydrodynamic force that pulls the rotor in the opposite direction. Finally, the results from time dependent simulations where the rotor can move unrestricted in axial position are discussed. Here, the influence of the time step is investigated, as well as the influence of geometric parameters and operating conditions.
Characterization of Powered Resonance Tube for High Frequency Actuation
Authors: Hamed A. , Das K. , Basu D.
Published: February 2009

A numerical investigation of powered resonance tube is carried out to study the effect of geometry on the unsteady flow characteristics and mass flow variations. Computational results for pressure fluctuations and sound pressure level (SPL) spectra are presented for different tube configurations. The results demonstrate that both amplitude and frequency for pressure oscillations in the gap are strongly dependent on tube length and separation distance.
Comparison of CFD Simulation to the Experiments for Forward Step Flows
Authors: Nakamura Shoichiro , Onuma Hiroyuki , Carswell Peter G.
Published: February 2009

Three dimensional DNS simulation on the fluid flow over a forward step configuration are compared with the experiments reported by Shakouchi, Ando, and Ito. This is a part of authors’ attempts to evaluate the validity of three dimensional unsteady flow simulation by comparison to experiments. Summary of the comparison is as follows: (1) vortex shedding in the flow separation over the top of the step near the corner is observed, (2) frequency of vortex shedding and distance between two consecutive vortices do not agree with the experiment, (3) however, while steady periodic shedding of vortices from the top corner of the step is reported for the experimental results, the computational results show unsteady behavior of the flow over the top corner, which results in unsteady shedding of vortices. This unsteadiness in the computational simulation is due to unsteady motion of fluid upstream from the step where adverse pressure increase occurs.
Experimental Determination of the Tonal Noise Sources in a Centrifugal Fan
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Santolaria-Morros Carlos , Hurtado-Cruz Juan Pablo
Published: February 2009

In this work, an experimental study about the aerodynamic tonal noise sources in an industrial centrifugal fan with backward-curved blades has been carried out. Acoustic pressure measurements at the fan exit duct and pressure fluctuation measurements on the volute surface (specially in the vicinity of the volute tongue) have been made for different flow rates. The correlation of both pressure signals can lead to determine the zone of effective acoustic radiation. As was expected, the tonal noise generation is concentrated on the meridional plane of the impeller discharge, near the volute tongue and presents a strong dependence with the flow rate.
Education to Stimulate Students Motivation: Activity Through the Factory for Dreams and Ideas
Authors: Hattori Yoichi
Published: February 2009

Kanazawa Institute of Technology (hereinafter KIT) started its education reform in April 1995. The basic principle behind the reform is to develop students who can learn autonomously. The idea comes from education inadequacies up to that time, where instructors “crammed” knowledge into students. KIT established the “Factory for Dreams and Ideas” (hereinafter “Yumekobo” which is the original Japanese name of the facility), a facility open to all KIT students. There they can create things any time they like. The students can utilize “Yumekobo” freely, in the same manner as a library. In Japan, the national holidays and Sundays total sixty-five days in a year leaving three hundred days for potential use of “Yumekobo”. University classes are in session one hundred and fifty days. This means it is necessary for KIT professors and instructors to come up with good strategies to have the students spend the remaining one hundred days in a productive way that will help students to raise their academic performance. To facilitate increased performance, KIT built a library center in 1982. There, learning takes place mainly through reading books. However, we felt that another new facility to stimulate students’ interest in creating things would be an excellent way to motivate further learning for the students. Here the author will explain present state of “Yumekobo” and how it has helped students continually seek to implement their ideas, especially through team activities.
Flow Distribution and Pressure Drop in Steady Airflow Through a Selective Laser Sintered Human Tracheobronchial Airway Model
Authors: Tan Kah-Hoe , Parthasarathy Ramkumar N. , Altan M. Cengiz , Johnson David L. , Clinkenbeard R. E.
Published: February 2009

The flow distribution and pressure drop of steady airflow in the human central airways were studied experimentally using an anatomically correct, selective laser sintered (SLS) human tracheobronchial airway model. Measurements were made for tracheal flow rates ranging from 0.1 to 2.67 liters per second, which correspond to normal physiological flow ranges. The mean air velocities at the exit orifices of the airway model were detected by means of a pitot static tube connected to a pressure transducer. The flow rates, the average velocities, and the Reynolds numbers in each branch of the airway model were then computed. In addition, the static pressure difference between the trachea and the airway exits was measured. The experimental measurements were used to determine the relationship between pressure drop and flow rate. The ratio of inlet to total exit area of the model was identified as a significant factor that influenced the pressure drop. The results obtained in the present study will be particularly useful for validating computational studies.
PIV Investigations of the Flow Field in the Volute of a Rotary Blood Pump
Authors: Sankovic J. M. , Kadambi J. R. , Mehta M. , Smith W. A. , Wernet M. P.
Published: February 2009

A full-size acrylic model of a rotary blood pump was developed in order to utilize Particle Image Velocimetry (PIV) to make measurements of the fluid velocities and turbulent stresses throughout the device. The development of an understanding of the hemodynamics within the blood pump is critical to the development and validation of computational models. A blood analog solution, consisting of sodium iodide solution and glycerin, was developed to match physiological kinematic viscosity. The refractive indecies of the fluid, the pump casing and the impeller were matched to facilitate the use of PIV to make velocity measurements. Velocity measurements made in the volute exit/diffuser region are presented for pumps speeds of 3000–3850 rpm. At each speed data were obtained at a physiological pressure of 90 mmHg and at a maximum flow condition. Four hundred data pairs were used for each resultant mean velocity vector value, representing greater than an order of magnitude more data pairs than reported previously in the literature on similar devices and resulting in velocity uncertainty levels of approximately ±2.9%.
Modeling of Cuttings Transport for Hole Cleaning in Horizontal and Highly Inclined Wells by Coiled Tubing Drilling
Authors: Takahashi Hiroshi
Published: February 2009

The purpose of this study is to develop the mathematical model on the limit deposit velocity for hole cleaning in coiled tubing drilling. The model was developed for coarse cuttings by using the two-layer model. It was found from the calculated results by using the developed model that the minimum flow rate to convey the coarse cuttings, that is critical flow rate, increases with increasing ROP (rate of penetration) in the range of low ROP. However, the critical flow rate showed a maximum at certain ROP and then the critical flow rate decreases gradually with increasing ROP. Furthermore, it was confirmed that the effect of well inclination angle and cuttings diameter on the critical flow rate was significant. This result indicates that the behavior of cuttings in the well should be monitored carefully by measuring the supplied mud flow rate and cuttings delivered to the ground surface.
Rheology Modifiers for Radioactive Waste Slurries
Authors: Kay Elizabeth D. , Calloway T. Bond , Koopman David C. , Brigmon Robin L. , Eibling Russell E.
Published: February 2009

One factor limiting the production rate of radioactive waste immobilization processes is the rheological limitations imposed by the design of remotely maintained slurry process equipment (i.e. pumps, piping). Rheology modifiers (dispersants/flocculants) that could potentially decrease the yield stress and/or plastic viscosity of radioactive waste slurries were tested on simulated waste to determine which provided the largest decrease in yield stress and plastic viscosity. The goals of this study were to: 1) determine if trace levels of chemical additives could be used to reduce the rheological characteristics of radioactive waste slurries, 2) identify potential chemical additives for this work and future testing, 3) test a limited set of chemical additive candidates on simulated radioactive wastes, and 4) develop advanced techniques to visualize the internal slurry structure and particle-particle interaction within the slurry. Radioactive wastes slurries generated from the production of plutonium and tritium during the Cold War are being (and will be) immobilized in a borosilicate glass matrix using joule heated glass melters at various Department of Energy (DOE) facilities located across the United States. The maximum insoluble solids content of the waste slurries is limited by the design-basis rheological properties (e.g. the Bingham plastic yield stress and plastic viscosity) used to design the slurry handling systems. It is possible to modify the equipment used to mix, sample, and transport the waste slurry. However, the design and construction cost for any such modifications is very high due to the constraints (radiation, non-visible remote operation) imposed on the design and operation of radioactive waste processes. The rheology of two slurries with various rheology modifiers was evaluated using a conventional concentric cylinder rheometer (Haake Rheometer RS150). Only one rheology modifier of those tested was found to decrease the apparent viscosity of the waste slurry by any significant amount and several of the modifiers tested produced the opposite effect. Duramax D-3005 was found to decrease the Bingham Plastic yield stress of simulated radioactive waste slurries by approximately 18%. Selected slurries were further analyzed by a laser scanning confocal microscope. This technique allows the slurry to be analyzed in an unaltered condition. The microscope has the ability to make both two-dimensional pictures and three-dimensional representations of the slurry’s internal structure. The microscope allows the user to understand how particles are flocculated or dispersed throughout a concentrated suspension of heterogeneous simulated nuclear waste slurries.
Visualization and Measurement of Mixing Process of Particles Into Water Jet
Authors: Monji Hideaki , Mizusaki Akiyo , Matsui Goichi , Ogiso Ryoji
Published: February 2009

A mixing process of catalyst particles into a fluid jet is a key part in a chemical reactor because the efficiency of chemical reaction depends on the particle catalyst distribution. Therefore, a mixing process of polystyrene particles into a water jet was investigated experimentally as a basic study of flow with catalysts in the chemical reactor. The velocity fields of both water and particles were measured by image processing. The main results obtained are as follows. The particle velocity approached to the water velocity at the mixing process, when the particles were entrained into the water jet. Because the particle concentration was very low, the velocity distributions were not changed by the addition of the particles. However, the turbulent intensity of the water increased comparing with the case of the water single phase jet.
Investigation of Flow Characteristics in a Coronary Artery Stent Using PIV
Authors: Yee Lauren K. , Kadambi J. R. , Wernet Mark P.
Published: February 2009

The complications resulting from coronary stenting are partly caused by alterations/disturbances in fluid dynamics of the arterial flow. To characterize flow within stented left anterior descending arteries at physiological rest conditions, an in vitro pulsatile flow loop and a micro-particle image velocimetry (PIV) system are developed. The highest and lowest velocities occur at the pumping period peak and the pump relaxation period commencement, respectively. Flow reversal exists at the start of pump relaxation. Recirculation regions at the stent leading and trailing edges and at edges of stent slots correlate to platelet deposition areas. The measured wall shear stresses are 5–15 dynes/cm2, which may inhibit re-endothelialization.
Numerical Simulation on Deformation and Entanglement of the Fibers in Dilute Fiber Suspension Flow
Authors: Ohno Masahiro , Iwasaki Kazuhisa , Hagiwara Yoshimichi
Published: February 2009

Numerical simulation has been carried out for laminar uniform flow or Couette flow with fibers, which is described with pearl-necklace models. The SHAKE algorithm has been refined in order to simulate the flexibility of fibers. The refined algorithm has been applied to the pearl-necklace model. The computational results show that the flexibility of fibers can be simulated by changing the constraint condition of the angle formed by three adjacent beads in a suitable range. The entanglement of fibers is found to be predicted by considering the effect of collision between the beads belonged to a different model.
Application of Numerical Techniques to Analysis of Jigging of Plastic Particles
Authors: Asakura Kuniomi , Oide Hiroyasu , Mizuno Midori , Tsunekawa Masami , Hirajima Tuyoshi
Published: February 2009

The separation performance of a jig classifier was studied numerically using mixtures of two and three types of spherical plastic particles. The fluid phase was solved by the SIMPLE scheme. Movement of each particle was simulated by a Lagrangian method including contact force calculated by the distinct element method. In the case of a mixture consisting of three types of spherical particles, the maximum difference in densities was set to be 0.01 g/cm3. The results of simulation showed that the jig classifier has good separation performance.
Lateral Vibration of Nonrotating Drill Pipe Conveying Fluid in Vertical Holes
Authors: Zhang Qun , Miska Stefan
Published: February 2009

A theoretical study has been performed on the lateral vibration of non-rotating drillpipe interacted with drilling fluid in vertical holes. Particular attention is paid to the interaction between drillpipe and drilling fluid near drillpipe neutral point zone. A new theoretical model has been established. The interaction between drillpipe and drilling fluid is characterized in this model. Dimensional analysis has been conducted to generalize this model. An innovative numerical method has been developed to solve the eigensystem. A FORTRAN program has been developed to model the behavior of drillpipe conveying fluid in vertical holes. Several numerical examples are provided to show the influences of drilling fluid on drillpipe dynamics. Fluid is considered to be flowing downward inside pipe and upward in annulus simultaneously. Results show that drilling fluid has significant influence on drillpipe dynamics.
Computational Fluid Dynamics Model for Tacoma Narrows Bridge Upgrade Project
Authors: Debus Kristian , Berkoe Jonathan , Rosendall Brigette , Shakib Farzin
Published: February 2009

The purpose of this work was to validate and apply a commercial computational fluid dynamics code with a hybrid RANS/LES turbulence computational model for a flow past a bluff body ultimately to help in the design of the caisson anchoring system during construction of a new adjacent span of the Tacoma Narrows Bridge.
Numerical Simulation of Vortex-Induced Vibration and Torsional Flutter of Rectangular Cross-Sections by k-ε Model
Authors: Shimada Kenji , Ishihara Takeshi
Published: February 2009

In this paper, torsional aeroelastic vibration is investigated by wind tunnel experiment and numerical analysis which incorporates 2-dimensional modified k-ε model. Experimental results shows that the torsional vortex-induced vibration are classified into several groups. Harmonics and of the Karman-vortex or impinging-shear-layer-instability are found to be involved with the occurrence mechanism of these instabilities. Two types of rectangular cross-sections are chosen to examine the applicability of the numerical method. Unsteady wind forces, pressure distribution and free vibrations are compared with experiments. Although the present method is 2-dimensional, vortex-induced vibrations and torsional flutter were well simulated by the method.
Vortex Shedding From Two Circular Cylinders in a Staggered Arrangement
Authors: Sumner D. , Richards M. D.
Published: February 2009

Vortex shedding from two circular cylinders of equal diameter in a staggered configuration was studied experimentally in the subcritical Reynolds number regime, for Re = 3.2×104–7.4×104. The dimensionless centre-to-centre pitch ratio of the staggered cylinders was ranged from P/D = 1.125–4.0, and the incidence angle was varied in small increments from α = 0°–90°. The behaviour of the Strouhal number measurements was broadly classified according to whether the cylinders were closely, moderately, or widely spaced, corresponding to P/D < 1.5, 1.5 ≤ P/D ≤ 2.5, and P/D > 2.5, respectively. For closely spaced staggered configurations, the flow around the cylinders is similar to a single bluff body, and only a single Strouhal number is measured. For moderately spaced cylinders, two distinct Strouhal numbers are measured when α > 30°, but there is considerable scatter in the Strouhal data when α < 30°. For widely spaced cylinders, the Strouhal numbers remain close to that of a single circular cylinder, in contrast to the behaviour of the aerodynamic forces. Evidence of the outer lift peak is seen in the power spectra for the downstream cylinder.
Vortex Shedding From Two Surface-Mounted Prismatic Obstacles in Lock-in Regime
Authors: Martinuzzi Robert J. , Havel Brian
Published: February 2009

Periodic vortex shedding from two surface-mounted cubes, of height H, in tandem arrangement placed in a thin boundary layer is investigated for a spacing 2H using phase-averaged laser Doppler velocimetry measurements. Tests were conducted for a Reynolds number of 22000, based on H and the freestream velocity, and an approximately 0.07H thick laminar boundary layer. For this obstacle spacing, the shedding frequency scales linearly with the obstacle spacing. It is shown that in this lock-in regime, periodic shedding is triggered by the displacement of the vertical flow along the front face of the downstream obstacle and is thus different from that observed for two-dimensional cylinders in uniform streams. The existence of this three-dimensional effect is then used to explain why lock-in cannot be observed for square cylinders in tandem arrangement.
Large Eddy Simulation of Turbulent Combustion Flow in a Gas-Turbine Combustor
Authors: Taniguchi Nobuyuki , Tominaga Takuji , Hashimoto Akiyoshi , Itoh Yuichi
Published: February 2009

In views of mechanical engineering, a primary problem in energy equipment design is to control of turbulent flows. Large eddy simulation is applied for analyzing tree-dimensional and unsteady features in gas-turbine combustor. For these purpose, LES with a G-equation flame model based on the flamelet concept is developed on the general co-ordinate grid and is demonstrated in design of a premixed gas-turbine combustor for aircraft engine. The simulations of the flame propagation are executed in some conditions with different relations of the equivalent ratios, and the flame positions and propagating behaviors are analyzed.
An Efficient Immersed-Boundary Method to Deal With Over 1000 Solid Particles in Liquid Flow
Authors: Kajishima Takeo
Published: February 2009

To deal with a number of solid bodies moving in fluid flow, we proposed an immersed-boundary method, in which the fortified Navier-Stokes equation was applied (Kajishima, et al., 2001). The fluid forces on the bodies are obtained by resolving flow around them. In this paper, some improvement for wider variety of flow conditions is introduced. Then a result of direct numerical simulation (DNS) of turbulence caused by over 1024 particles falling by gravity is demonstrated with particular interest on the influence of particle rotation.
TopMaker: A Technique for Automatic Multi-Block Topology Generation Using the Medial Axis
Authors: Rigby David
Published: February 2009

A two-dimensional multi-block topology generation technique has been developed. Very general configurations are addressable by the technique. A configuration is defined by a collection of non-intersecting closed curves, which will be referred to as loops. More than a single loop implies that holes exist in the domain, which poses no problem. This technique requires only the medial vertices and the touch points that define each vertex. From the information about the medial vertices, the connectivity between medial vertices is generated. The physical shape of the medial edge is not required. By applying a few simple rules to each medial edge, the multi-block topology is generated with no user intervention required. The resulting topologies contain only the level of complexity dictated by the configurations. Grid lines remain attached to the boundary except at sharp concave turns where a change in index family is introduced as would be desired. Keeping grid lines attached to the boundary is especially important in the area of computational fluid dynamics where highly clustered grids are used near no-slip boundaries. This technique is simple and robust and can easily be incorporated into the overall grid generation process.
Improvement of Searching Nodes Arithmetic in Meshfree Method
Authors: Qiu Yi , You Changfu , Qi Haiying , Xu Xuchang
Published: February 2009

In numerical simulation with meshfree method, it is necessary to search nodes that are needed. In dealing with complex problems, there must be a great number of nodes distributed in computational domain. If a conventional Node-Searching method is used here, it will be a burdensome task for the computer. So this paper proposes a new numerical arithmetic, Domain-Dividing method, which means that the domain can be divided into several subdomains. With this method, we can search only those corresponding subdomains instead of the entire domain for nodes. This paper adopts the Node-Searching arithmetic to simulate the inviscid potential flow over a cylinder, and it is found that with the increase of the nodes in domain, the computational time of meshfree method is increasingly longer than that of finite element method, but compared with meshfree method using conventional Node-Searching method, the arithmetic proposed in this paper can reduce much more time for searching nodes.
Hydrodynamic Model for Microscale Flows in a Channel With Two 90° Bends
Authors: Raju Reni , Roy Subrata
Published: February 2009

Many microfluidic devices require serpentine channels to allow longer contact length within a compact area. The necessity of understanding the physical laws governing these complicated small geometries is crucial for better design of practical microfluidic systems. At micro-scales the continuum assumption of standard Navier-Stokes equation is no longer valid as the mean free path of the fluid becomes comparable to the dimension of the system. A finite element based hydrodynamic algorithm has been developed recently for analyzing slip flows through two-dimensional micro geometries. This paper documents numerical results for gas flow through a micro-column with two sharp 90° bends. The results obtained show increase in slip effect for higher pressure ratios. To the best of our knowledge, this is the first such published report addressing microflow in this particular geometry.
A New Computational Method for Dynamic Behaviour of Two-Dimensional Free Surface
Authors: Hirata Katsuya , Tanigawa Hirochika , Funaki Jiro , Kitano Tatsuya
Published: February 2009

A new method is proposed in order to compute dynamic behaviours of a liquid free surface. The method is based on a discrete singularity method, and enables us to simulate sloshing problems very easily and efficiently. The authors consider the free surface in a two-dimensional rectangular container that is vibrated vertically. It was found that there is the optimum clearance of singularity from a boundary, which makes surface error minimum. Furthermore, the authors conducted some experiments, and have observed three sloshing modes, and their stability regions. Then, we confirm that for the method is effective for 2D-sloshing problems.
Numerical Simulation of Water Quenching Process of an Engine Cylinder Head
Authors: Wang De Ming , Alajbegovic Ales , Su Xuming , Jan James
Published: February 2009

Presented is a simulation of an engine cylinder head undergoing water quenching process using a recently developed approach for modeling quenching cooling of metal parts (Wang et al., 2002). The approach is based on the AVL SWIFT Eulerian two-fluid method with special emphasis on handling high mass exchange rate associated with quenching. A tetrahedral grid of 830,000 cells is generated for the computational domain, which includes the solid part of the cylinder head immersed in the fluid. Detailed vapor and temperature distributions are obtained which offer valuable information for the thermal stress analysis. It is observed that the temperature field within the cylinder head is highly non-uniform. The computed cylinder head monitoring point temperature versus time is compared with that registered by the thermal couple measurement. Reasonable agreement is observed. The simulation exercise may potentially be used to identify the cause of cracks often encountered in quenching heat treatment thereby lead to a better design of the process.
Interfacial Structures and Regime Transition in Co-Current Downward Bubbly Flow
Authors: Kim S. , Paranjape S. S. , Ishii M. , Kelly J.
Published: February 2009

The vertical co-current downward air-water two-phase flow was studied under adiabatic condition. In view of studying the effect of flow area on interfacial structure and regime transition, round tubes of 25.4-mm ID and 50.8-mm ID were employed as test sections. The flow regime map was constructed for each test section by employing a newer approach. Unlike the conventional flow visualization method, the present approach minimizes the subjective judgment in determining the flow regimes. It was found that the flow regime in the co-current downward flow strongly depend on the channel size. The local two-phase flow parameters were acquired by the multi-sensor miniaturized conductivity probe in bubbly flow. They include: the local time-averaged void fraction, interfacial area concentration, bubble velocity and bubble Sauter mean diameter. The area-averaged data acquired by the impedance void meter were analyzed by the drift flux model. Three different distributions parameters were developed for the different ranges of non-dimensional superficial velocity, defined by the ration of total superficial velocity to the drift velocity. The new correlations can be applied to a co-current downward two-phase flow in a wide range of flow regime spanning from bubbly to annular flow.
Mechanistic Models for Droplet Formation and Breakup
Authors: Kouba Gene E.
Published: February 2009

Mechanistic models are created to predict the smallest droplet or bubble of a low concentration, inviscid, dispersed fluid that can be formed by shear from the continuous fluid (or droplet impact on a wall) and the largest droplet/bubble that can survive in a shear flow. Weber number criteria are developed for both the smallest and largest droplet/bubbles based on energy and force balances. The droplet deformation is predicted from an energy balance between available energy from drag on the droplet and energy required to deform the droplet. Different droplet deformation geometries are incorporated into the deformation model and compared against available data from the literature. The oblate spheroid deformation was found to provide the better prediction of deformation, terminal velocity, and largest droplet than a sphere, disk or spherical segment. The droplet deformation and breakup models are believed to be applicable to breakup of droplets, bubbles, and dual dispersions in a wide variety of conditions. These relatively simple models compare favorably against experimental data for low viscosity dispersed liquids and have been successfully used to predict liquid carry-over and gas carry-under from various gas/liquid separators. These models have been incorporated into simulation software used to design predict performance of compact separation equipment.
Two-Phase Flow in Liquid Filled Vessels During the Depressurization by Periodic Venting
Authors: Mewes Dieter , Schmitz Dirk
Published: February 2009

Pressurized chemical reactors or storage vessels are often partly filled with liquid mixtures of reacting components. In case of an unexpected and uncontrolled exothermic reaction the temperature might increase. By this the pressure follows and would exceed a critical maximum value if there would be no mechanism to decrease the pressure and the temperature in a very short period of time. A sudden venting by the opening of a safety valve or a rupture disc causes a rapid vaporization of the reacting liquid mixture. A two-phase flow will pass the ventline. Since two-phase gas-liquid flows cause high pressure losses and give rise to limited mass flows leaving the reactor, single-phase gas flows are preferred. This is emphasized by a periodic venting mechanism of the pressurized vessel. Each time the two-phase flow from the bubbling-up liquid inside the vessel reaches a certain cross-section close the entrance of the ventline. The outlet-valve is closed. Inside the vessel the increasing pressure stops the two-phase flow and only single phase flow is leaving the vessel. The two-phase bubbly flow inside the vessel is detected by a tomographic measurement device during the venting process. Experimental results for local and time dependant phase void fractions as well as pressures are compared with those obtained by numerical calculations of the instationary bubble swarm behavior inside the vessel.
The Modeling of Thin Liquid Films Along Inclined Surfaces
Authors: Podowski Michael Z. , Kumbaro Anela
Published: February 2009

This paper is concerned with the analysis of thin and ultra-thin liquid films. The results are applicable to various geometrical and kinematic conditions, including both stationary and moving surfaces. The new results obtained in this work include: • the derivation of an analytical solution for the evolution of film thickness over the entire multiscale range, from the liquid free surface to the asymptotic (disjoining-pressure controlled) region, and for any surface inclination angle between 0° to 90°, • the formulation of a method to deduce the Hamaker constant based on a single measured value of film thickness at the beginning of the disjoining-pressure-controlled region, applicable to any inclination angle, • the explanation of the reasons why the thickness of liquid films on moving surfaces is normally beyond the range of Van der Waals forces, • the formulation of an expression for the nondimensional asymptotic film thickness as a function of the capillary number; this new result explicitly accounts for the effect of gravity on the average film velocity.
The ‘Characteristics-Based Matching’ (CBM) Method for Compressible Flow With Moving Boundaries and Interfaces
Authors: Nourgaliev Robert , Dinh Nam , Theofanous Theo
Published: February 2009

Recently, Eulerian methods for capturing interfaces in multi-fluid problems become increasingly popular. While these methods can effectively handle significant deformations of interface, they have been known to produce nonphysical oscillations near material interfaces due to the smeared out density profile and radical change in equation of state across a material interface. One promising recent development to overcome these problems is the ‘Ghost Fluid Method’ (GFM). While being able to produce excellent results for simulation of gas-gas flows, the GFM boundary treatment is unsatisfactory for the case of liquid-liquid or liquid-gas compressible flows. The present study devotes to a new methodology for boundary condition capturing in multi-fluid compressible flows. The method, named ‘Characteristics-Based Matching (CBM)’, capitalizes on the recent development of the level set method and related techniques, i.e., PDE-based re-initialization and extrapolation, and the ‘Ghost Fluid Method’ (GFM). Specifically, the CBM utilizes the level set function to ‘capture’ interface position and a GFM-like strategy to tag computational nodes. In difference to the GFM method, which employs a boundary condition capturing in primitive variables, the CBM method implements boundary conditions based on a characteristic decomposition in the direction normal to the boundary. Since the method allows to avoid over-specification of boundary conditions by respecting the information flow, we believe that the CBM is able to ‘cure’ above-mentioned problems of the GFM boundary condition capturing technique. In this paper, the method’s performance is examined on fluid dynamics problems with stationary and moving boundaries. Numerical results agree well with known analytical or computational solutions and experimental data. Robust and accurate solutions were obtained. In particular, spurious over/under-heating errors, typical for moving boundary treatment by other methods, are essentially eliminated in the CBM solutions.
Bubble Size Effects on Dispersed Phase Motion in Vertical Bubbly Pipe Flow
Authors: Nikitopoulos D. E. , Fiedler J. , Dowden M. , Evans E.
Published: February 2009

Three-dimensional measurements of bubble size, and velocity are presented along with the associated statistics for dilute bubbly flow in a vertical pipe. These measurements were obtained through a combination of precise index-of-refraction matching and a stereoscopic high-speed imaging system. An image-processing algorithm has been developed and used to extract instantaneous bubble size, shape, velocity and trajectory information and statistics corrected for magnification errors (maximum of 2%). The experiments have been conducted at a Reynolds of 14,600 in vertical pipe-flow and a volumetric gas flow ratio of 0.29%. Bubble sizes ranged from sub millimeter to several millimeters. The results indicate that bubbles less than approximately 20 wall units with very low ratios of rise velocity-to-liquid-average-velocity occupy the full breadth of the test section, while bubbles in the range between 20 and 60 wall units with ratios of rise-velocity-to-liquid-average-velocity greater than 0.5 are efficiently trapped by the wall and are almost exclusively found in the inner wall region (y+ < 30). Bubbles larger than 60 wall units with ratios of rise-velocity-to-liquid-average-velocity less than 0.5 are found throughout the pipe cross-section although with a strong preference to the wall neighborhood. This bubble behavior is put in perspective considering four mechanisms of bubble migration: (a) turbulent dispersion due to near-wall large scale structure, (b) inviscid transverse forces (Magnus), (c) viscous transverse forces (Saffman), and (d) unsteady transverse forces because of vortex shedding and bubble shape deformation.
Surfactant Use for Slug Flow Pattern Suppression in a Horizontal Pipe
Authors: Wilkens R. J. , Glassmeyer S. R. , Rosebrock G. J. , Storage K. M. , Storage T. M.
Published: February 2009

A set of experiments was performed to study flow pattern suppression in gas-liquid pipe flow by means of surfactant additive. Results suggest that addition of the surfactant to gas-liquid flow significantly reduces the occurrence of slug flow. In addition, previously unreported flow patterns were observed to exist between slug and dispersed bubble flows. It is concluded that new mechanisms for slug flow transition need to be considered.
The Modeling of Lift and Dispersion Forces in Two-Fluid Model Simulations: Part I — Jet Flows
Authors: Lopez de Bertodano M. , Moraga F. J. , Drew D. A. , Lahey R. T.
Published: February 2009

Two-fluid model simulations of a bubbly vertical jet are presented. The purpose of these simulations is to assess the modeling of turbulence dispersion and lift forces in a free shear flow. Although turbulence dispersion forces have previously been validated using simpler canonical flows and microscopic particles or bubbles, there was a need to asses the model performance for larger bubbles in more turbulent flows. This method, of validating two-fluid models in flows of increasing complexity has the advantage of excluding, or at least minimizing, the possibility of cancellation of errors when modeling several forces. In a companion paper (see Part-II), the present two-fluid model is extended to a boundary layer in which forces induced by the presence of a wall are important. The turbulent dispersion models used herein are based on the application of a kinetic transport equation, similar to Boltzmann’s equation, to obtain the turbulent diffusion force for the dispersed phase [1, 2]. They have already been constituted and validated for the case of particles in homogeneous turbulence and jets [3] and for microscopic bubbles in grid generated turbulence and mixing layers [4]. It was found that it is possible to simulate the experimental data in Ref. [5] (See Figures-1 to 4) for a bubbly jet with 1 mm diameter bubbles. Good agreement is obtained using the model of Brucato et al. [7] for the modulation of the drag force by the liquid phase turbulence and a constant lift coefficient, CL. However, little sensitivity is observed to the value of the lift coefficient in the range 0 < CL < 0.29.
The Modeling of Lift and Dispersion Forces in Two-Fluid Model Simulations: Part II — Boundary Layer Flows
Authors: Moraga F. J. , Lopez de Bertodano M. , Drew D. A. , Lahey R. T.
Published: February 2009

Two-fluid model simulations of a bubbly vertical boundary layer with point injection are presented. A new bubble turbulence dispersion model, designed to be used with RANS type turbulence models, was formulated and compared with recent data of [1] and [2]. These data showed that bubble migration toward the wall is controlled by the coherent large scale liquid structures within the boundary layer. The model is based on the application of a kinetic transport equation, similar to Boltzmann’s equation, and the idea that by selectively removing bubbles from the liquid eddies within the boundary layer, bubble capture at the wall introduces a preferential direction of migration and/or nonhomogeneous, anisotropic dispersion. This is the first model capable of predicting all the types of void fraction profiles observed experimentally for point injection. It is shown that without this new model, two-fluid model simulations fail to predict the experimental data. In addition, a new physical interpretation of the data of [1] and [2] is presented, which strongly suggests that the quantity controlling bubble migration toward the wall and bubble dispersion, is the boundary layer drift parameter (i.e., the ratio of the bubble’s terminal velocity to the free-stream liquid velocity).
Wake Disappearance and Mean Flow Results for Multibody and Multiphase Flows
Authors: Eames I. , Hunt J. C. R. , Belcher S. E.
Published: February 2009

Complex multibody and multiphase flow problems represent a significant challenge to describe computationally and to study experimentally. In this paper we describe two main physical processes, which are studied analytically and which have a wide bearing on bubbly flows. The first is the general phenomena of vorticity annihilation which occurs when in the presence of straining motion generated by neighbouring bodies or through wakes intermingling with their neighbours. The second is blocking due to the flow having to go around these bubbles, which is studied using inviscid flow theory. By applying a new methodology, we provide a clear physical argument for drift-flux correlations typically assumed in multiphase models. Finally, we show how the two processes, vorticitiy annihilation and blocking, can be combined within one theoretical model and the consequences for modeling multibody and multiphase flows.
A Non-Invasive Liquid Film Thickness Measurement
Authors: Giroud-Garapon S. , Heid G. , Lavergne G. , Simonin O.
Published: February 2009

Wall spray interactions play an important role in the combustion efficiency prediction of turbojet or ramjet. They generate complex physical phenomena such as rebound onto wall or rebound onto wetted surface, splashing, deposition, film formation, film streaming and film atomization. ONERA/DMAE has been working on these subjects for few years, and some wall-drop interaction models have been developed and integrated into CFD-industrial-codes. In order to improve this work, a basic experimental study has been performed to analyze wall liquid film inside a combustion chamber. This is a cold flow experiment, where a liquid film is flowing on a hot tilted plate put on the bottom wall of the tunnel. Ethanol enriched with fluoresceine is used as fuel. The liquid emerges from a pipe with a diameter of 1 mm. Afterwards the film flow is canalized in a groove. It is streaming on the hot plate which temperature should be fixed from 300 K to 700 K by an element heating controlled electronically. The film thickness is measured with a non-intrusive technique based on the laser trace displacement at the liquid film interface. Indeed, when the film thickness varies, the trace of the laser plan is moving. Thus, it is enough to know the optical magnification used and the angle of the CCD camera to obtain the film thickness. This technique gives only the thickness of the film, so its velocity has to be estimated using flow rate conservation. The goal of the present experiment is to create an experimental data-base on wall liquid film behavior in terms of thickness, velocity and surface instabilities evolution (with an FFT analysis) for numerical comparison.
Experimental Investigation of the Effect of Camber on the Aerodynamic Characteristics of Airfoils in Ground Effect
Authors: Ahmed M. R. , Imran G. M. , Sharma S. D.
Published: February 2009

In the present paper, results from an experimental investigation of aerodynamic ground effect on two airfoils are presented. The flow characteristics over a symmetrical airfoil (NACA 0015) and a cambered airfoil (NACA 4415) were studied in a low speed wind tunnel. Experiments were carried out by varying the angle of attack from 0° to 10° and ground clearance from zero to one chord length. Pressure distribution on the surface of the airfoil was obtained with the help of pressure tappings. Mean velocity distributions were obtained over the surface of the airfoil. Profiles of mean velocity and turbulence intensity were obtained in the wake region at 0.5 and 1.0 chord length downstream of the trailing edge. It is found that pressure increases on the lower surface as the ground is approached. The flow accelerates over the airfoil, and a considerably higher mean velocity is observed near the suction peak location. For the symmetrical airfoil, the mean velocity over the surface was found to increase by nearly 30%, while for the cambered airfoil, an increase of nearly 60% was recorded for an angle of attack of 7.5°. The flow was found to separate almost near the trailing edge for angles of attack upto 10°, resulting in a thinner wake region and lower turbulence intensities for the symmetrical airfoil; while for the cambered airfoil, an early separation for an angle of attack of 10° was observed. Measurements in the wake region showed a defect in mean velocity profile at the corresponding values of ground clearance. For lower angles of attack, turbulence levels were higher in the wake region for the symmetrical airfoil, while for an angle of attack of 10°, very large defect in velocity was observed for the cambered airfoil model and the minimum velocity reduced to 20% of the freestream velocity.