bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Laboratory Experiments in Engineering Education
Authors: Gany Alon
Published: July 2009

The role of students experience in laboratory tests as a part of their engineering education is discussed. Nowadays, when computer simulations become an important tool in engineering design, problems solution, and research, students may loose the touch of real-world hardware and challenges. Hence, exposure to experimental work is very significant. It is proposed that at the advanced stages of the first degree studies, experiments related to specific courses will be incorporated as a part of the course material. It is also believed that in studies towards higher degrees, the combination of experimental research with theoretical modeling and analysis is an excellent introduction for the future professional career.
Seepage Regime in Canyon Mass With Influence of Water-Storage Reservoir Impoundment Speed
Authors: Kalabegishvili M.
Published: July 2009

Generally, most waterpower plants have to function under energy system peak load operation. Thus, there is a relatively quick water level variation observed in water-storage reservoirs, which contributes to the problems, especially in case of high-pressure waterworks facilities. Swift reservoir draw-down enhances seepage volumetric forces acting from the rock mass, which may lead to rock mass cracking and eventually to the development of landslide processes. A rapid impoundment of the water-storage reservoir is no less damaging. In this case, seepage in the rock mass is progressing in non-steady conditions, there occurring, in the inception stage: - high magnitude seepage hydrodynamic forces at the rock mass surface, creating additional loads on the rock mass, causing deflection of its surface, which may promote dam-foundation contact opening; - with increased pore pressures and seepage gradients, there may occur suffusion and other undesirable processes in the rock mass. In the work is given a numerical analysis of some parameters of seepage mode given based on right-bank investigation admitting presence of break in the dam filling-up mode. Options of time-intervals for the two basic versions – in case of sudden rising of water level in the upstream and in case of slow filling-up and setting up steady-state seepage mode in the massive – are being discussed. Determination of seepage flow parameters (including gradients) requires nonstationary field task to be solved. Finite-elements approximation for time analysis of the task is solved by finite-difference scheme. Seepage calculations are carried out by cyclic-iteration scheme – where volumetric water content, hydraulic conductivity and elasticity module determined numerically by functional relations. The subject of research is Enguri waterpower plant arch dam, at present the highest in the world (Georgia, height 271.5m, fig. 1.1). Consideration is being given to a variety of cases: - canyon slope in the zone of major geological fracture; - foundation in the central part of the dam.
Liquid-Phase Sintering of Tungsten Carbide-Cobalt by Laser Radiation
Authors: Glaeser Thorsten , Demmer Axel , Klocke Fritz
Published: July 2009

Laser Sintering is a powder metallurgical process. The principle of Laser Sintering is based on a local densification of powdered materials as a result of the absorption of laser radiation. Through a cyclic repetition of material application, densification and the lowering of a build-up plate, a three dimensional geometry develops. Within the Laser Sintering (liquid-phase sintering) of tungsten carbide-cobalt (WC-Co) the low melting material, the metal binder phase cobalt, is temporarily transferred into the liquid phase. The high melting WCphase is not melted and remains fine dispersed in the metal binder phase after cooling of the material.
Integrating Non-CAD Data With Reverse Engineering Tools
Authors: Retter Yoram
Published: July 2009

Aircraft design may require use of geometry that is not readable by the CAD system being used. Most notably, since aircrafts always stay in service longer than the CAD system that helped build them, such geometry will be pre-CAD real aircraft parts and the tools for manufacturing them. Other cases are data from deformed parts (real and virtual), output from analysis programs and flexible parts in a given position. Geometry from these sources can be read by the CAD system using Reverse Engineering tools and then be further processed in computer applications as required, either by itself or combined with CAD data from other sources. While this is not an every day requirement, the cases that do require such data usually have no other practical solution. This paper describes the practices used at IAI for such procedures and the lessons learned.
Solutions for Modelling the Energy Input in Electron Beam Material Processing
Authors: Zaeh Michael F. , Lutzmann Stefan , Branner Gregor , Strasser Gerhard
Published: July 2009

Additive Layer manufacturing methods constitute an interesting alternative with respect to the production of small series and customized products. Among other advantages, these methods offer an extensive flexibility concerning end customer parts (Rapid Manufacturing) or tools for prototypes and small batches (Rapid Tooling). Up to recent years, machines using laser beams for the solidification of powder material, e.g. Selective Laser Melting, were available on the world market. However, the extensive use of the electron beam in manufacturing processes like welding or perforating revealed its considerable potentials. These are, among others, fast beam deflection, high beam power density as well as high efficiency. Therefore, commercial organizations and research institutions like the iwb make use of this energy source in additive layer manufacturing. The resulting technology Electron Beam Sintering (EBS) is characterized by a complex interaction of various process parameters. In this paper, methods of numerical simulation are used in order to model the process sequence of solidification and to define the governing factors. The heat transfer into the powder bed has been identified as a vital aspect concerning the process stability and the resulting part quality. Therefore, the interaction between beam and powder material is being examined in detail. First, the process is subdivided into discretized solidification steps which enable the definition of a certain system boundary. Second, the determining differential equations are being formed and, due to various boundary conditions, solved using a commercially available software package, implying the Finite Element Method (FEM). Third, the necessary energy input into the powder can be determined and finally, experimental series are being conducted in order to validate the numerical results and identify optimum process parameters.
Entropy Generation in a Solid Oxide Fuel Cell
Authors: Sciacovelli Adriano , Verda Vittorio
Published: July 2009

The aim of the paper is to investigate possible improvements in the design of solid oxide fuel cells (SOFC). The first improvement is conducted on the system, by performing a second law analysis at component level. The analysis is then performed on the fuel cell. To achieve this purpose, a CFD model of the cell is used. The model includes energy equation, fluid dynamics in the channels and in porous media, current transfer, chemical reactions and electrochemistry. The analysis of the cell performances is conducted on the basis of the entropy generation. The use of this technique makes it possible to identify the phenomena provoking the main irreversibilities, understand their causes and propose changes in the system design and operation. The different contributions to the entropy generation are analyzed in order to develop new geometries that increase the fuel cell efficiency.
Structured Optimization
Authors: Sperati Maurizio
Published: July 2009

The interaction of computer aided design and 3D visualization techniques, as well as that of finite elements calculation techniques, has in this past decade speed up the process of product development by almost one unit measure. The possibility to anticipate physical problems through virtual reality has reduced the number of corrections and modifications that had to be made due to unforeseen behaviour. This in turn has allowed companies to refine the quality and performance of their products. Altair Engineering, being a software developer as well as a user of such software, is one of the major supporters of simulation technology and computer assisted product engineering methods. In developing Enterprise Solutions engineering software one must take into account the following criteria: • The speed at which results can be obtained; • The reliability of the results; • The time necessary to prepare inputs; • The time necessary to analyze results; • The way to store the results, make them available and communicate them. All of the above criteria can be subject to optimization in the most general sense of the word: obtaining the best results in the least time and minimum use of resources.
Aluminum Shield Under Hypervelocity Impact of Mylar Flyer
Authors: Zhao J. , Tan F. , Liu C. , Sun C.
Published: July 2009

The near-earth space environment is cluttered with man-made debris and naturally occurring meteoroids, which is a big menace to the safety of satellites and spacecrafts. This paper is addressed on the failure response of aluminum shields under hypervelocity impact of milligrame level flyer. A compacted electric gun is employed to accelerate a mylar flyer up to 10 km/s. Failure response of Ly12 aluminum shields with different thickness and layers impacted by mylar flyer with different velocities is under investigation. The spallation is observed in the rear free surface of 4 mm thick monolithic aluminum shield, and its fracture mechanism changes from plastic to brittle when loading pressure is above 13 GPa. A perforation with a diameter 8 mm in the impacted area of the 4mm thick Ly12 shield is observed after which is impacted by 0.1 mm thick mylar flyer 8mm in diameter with velocity 8.2 km/s. When three layers of shields are impacted, the debris clouds (DC) are observed in the first and the second spaces respectively during the impact process by high speed camera, and its leftover can be observed on the surface of the third plate. The shape of the first debris cloud head is a little flat, and its speed of lateral expansion is very slow, which is different from those impacted by spherical projectile, and its formation mechanics mainly attributes to multi-spallations based on the analysis of simulation.
Nonlinear Modelling and Identification of a Small-Scale Bridge
Authors: Zapico Jose´ L. , Bassir David H. , Gonza´lez-Marti´nez Mari´a P. , Garci´a-Die´guez Marta
Published: July 2009

The dynamic modelling and identification of a small-scale bridge is addressed in this paper. Two finite element models with linear elastic stiffness and different damping modelling has been tried. They correspond to a linear viscous damping and a nonlinear elasto-slip one. Both models were fitted to the available experimental data by a novel adaptive sampling technique that was repeated several times. In all the runs the technique yielded consistent results, which confirms its robustness. The elasto-slip model gave excellent fitting to the experimental data, while the results of the linear viscous one were poor.
Identification of Form Features in Non-Manifold Shapes Through a Decomposition Approach
Authors: De Floriani Leila , Hui Annie , Giannini Franca
Published: July 2009

In Computer-Aided Design (CAD), the idealization process reduces the complexity of the model of a solid object, thus resulting in a simplified representation which captures only the essential elements of its shape. Form features extraction is a relevant issue in order to recover semantic information from an idealized object model, since such information is typically lost during the idealization process. An idealized model is usually composed of non-manifold parts, whose topology carries significant structural information about the object shape. To this aim, we define form features for non-manifold object by extending the taxonomy of form features provided by STEP [19]. We describe an approach for the identification of features, which interact with non-manifold singularities in the object, based on a decomposition of a non-manifold object into nearly manifold components and on the properties of the graph representing such decomposition.
A MEMS-Based Rate Gyro Based on Parametric Resonance
Authors: Miller Nicholas J. , Shaw Steven W. , Oropeza-Ramos Laura A. , Turner Kimberly L.
Published: July 2009

This paper describes the dynamics of a microelectromechanical rate gyro whose operation depends on nonlinear parametric resonant response. The basic idea behind this and other similar gyros is that a proof mass is free to move in a plane such that the perpendicular directions of motion are ideally mechanically uncoupled. In one direction, the drive mode, the mass is parametrically driven such that it undergoes a nonlinear resonant response. When rotated about an axis perpendicular to the plane of motion, Coriolis effects couple this drive mode to the other direction, the sense mode, whose response is then measured and calibrated with the rotation rate. Traditional rate gyros of this type require precise matching of the drive and sense linear natural frequencies in order to optimally amplify the sense response. By making use of the wide frequency range of the nonlinear resonant response, many of the difficulties associated with this tuning problem can be avoided. In this paper we emphasize results from a simple two degree-of-freedom micro-electro-mechanical system model that allows one to predict and design the rate response of the gyro by selection of system parameters.
Analytical Prediction of the Transition to Chaos in Lorenz System
Authors: Vadasz Peter
Published: July 2009

The failure of the linear stability analysis to predict accurately the transition point from steady to chaotic solutions in Lorenz equations motivates this study. A weak non-linear solution to the problem is shown to produce an accurate analytical expression for the transition point as long as the validity condition and consequent accuracy of the latter solution is fulfilled. The analytical results are compared to accurate computational solutions showing an excellent fit within the validity domain of the analytical solution.
Comparative Hydrodynamic Analysis of the Bimanual Phacoemulsification Technique in Cataract Surgery
Authors: Spirochkin Yury K.
Published: July 2009

The phacoemulsification method used in cataract surgery is considered. In general, it can be realized by two different techniques. The most widespread technique is based on the use of instruments combining both the function of aspiration of crystalline lens fragments and the function of irrigation of substituting fluid in the same coaxial tip. The bimanual phacoemulsification is an alternative technique, which means carrying out of aspiration and irrigation by two divided tips. Advantages of the bimanual technique are revealed by hydrodynamic analysis on base of simplified mathematical modeling of flows arising in the eye anterior chamber during surgical operation. The data of this analysis compared with according data of coaxial technique allows getting convincing proofs of preferences of the bimanual technique because it decreases adverse hydrodynamic effect on the eye tissue, reduces consumption of replacing fluid and operation time. All these items make immediate positive influence on the quality of surgery.
Experiences With Advanced Pedagogical Approaches at Slovak Universities
Authors: Molna´r Pavol
Published: July 2009

• Blended learning (face-to-face and online learning) as basic component in creating the right environment for professional language learning. • Experience with Leonardo da Vinci Project REDILEM and the exploitation of its social and economic benefits for learners, existing and perspective entrepreneurs, managers and other beneficiaries. • Distance learning — the most important possibility of improving access to continuous vocational training and lifelong education in regions. • Advantages and some obstacles in distance (e-learning) education.
Stability Analysis of a Compliant Lemon Bore Journal Bearing
Authors: Kuznetsov Evgeny , Glavatskih Sergei
Published: July 2009

Dynamic coefficients for a lemon bore journal bearing with a compliant PTFE surface are computed. An efficient method for the calculation of bearing dynamic coefficients proposed by Lund [4] has been extended to compliant bearings. Comparison with a rigid babbitted lemon bore journal bearing in terms of dynamic coefficients and stability is given and discussed. It is shown that it is important to consider perturbations of both the oil film and the compliant lining to obtain realistic results. It is also shown that stability of compliant bearings is improved at some eccentricities compared with conventional babbitted bearings.
Co-Evolution Genetic Algorithm for UAV Distributed Tracking in Urban Environments
Authors: Shaferman Vitaly , Shima Tal
Published: July 2009

A distributed approach is proposed for planning a cooperative tracking task for a team of unmanned aerial vehicles (UAVs). In the scenario of interest UAVs are required to autonomously track, using their onboard sensors, a moving target in a known urban environment. The solution methodology involves finding visibility regions, from which a UAV can maintain a line of sight to the target during the scenario; and restricted regions, in which a UAV can not fly, due to the presence of buildings or other airspace limitations. A co-evolution genetic algorithm is derived for searching, in realtime, monotonically improving solutions. In the proposed distributed search method every UAV iteratively manipulates its own population of chromosomes, each encoding its control inputs in the calculated horizon. Team performance is attained by assigning fitness to each solution in the population based on the cooperative performance when using it together with preceding iteration tracking information obtained from teammates. Important attributes of the proposed solution approach are its scalability and robustness; and consequently it can be applied to large sized problems and adapt to the loss of UAV team members. The distributed nature of the algorithm also reduces the computation and communication loads. The performance of the algorithm is studied using a high fidelity simulation test-bed incorporating a visual database of the city of Tel-Aviv, Israel.
Integral PLM Solution to Product Development Challenges and Supporting Technologies
Authors: Reitman Michael A.
Published: July 2009

Product development today is more complex and more difficult than ever. Manufacturers face significant challenges understanding the full impact of changes proposed at various stages of development, and demand for collaboration is at an all-time high. At the same time Product Development differs from Manufacturing in that the objective is to create a digitally validated representation of the product and manufacturing processes, rather than physical product. The flow of digital product and process information between the different stakeholders involved in product development is critical to the performance of product development processes. The main challenge is to create and communicate this information with minimum waste. Product Lifecycle Management (PLM) offers the solution from planning to support, across all applicable departments, and throughout the entire supply chain. By working with complete digital product representations, teams can quickly experiment, make changes, perform what-if scenarios, refine designs, and more. Technologies supporting product development processes notably define and impact the information flow. When product development technologies involve multiple point solutions that manage independent views of the digital Product (i.e., the MCAD view, the BOM view, the cost view) it is nearly impossible for various users to piece together a consistent picture or maintain integrity between the views. Product development environment with multiple disconnected tools and databases that house different information product is still common. There are many barriers to information transfer and availability — and as a result there is little information flow. At a high level, an integral product development system, a single source of truth for product data whose components are designed to work together seamlessly, can greatly streamline information flow. Information fidelity is not compromised, and as a result information flows rapidly and consistently. PTC’s Product Development System (PDS) represents such integrated PLM solution that manages interdependencies across all forms of product information, so that everyone on the team can easily understand how their input impacts the overall product. There are key process principles or initiatives that a company may choose to focus on to reduce waste in product development: front loading, visual planning and tracking, standardizing work, systematic knowledge capture and reuse, closer manufacturing and supplier partnering, and improving the efficiency of review or collaboration activities. This lecture is going to focus on making the connection with relevant technologies that can play a critical supporting role, and on software components of Product Development System representing corresponding technology enablers.
Dimensional Analysis to Predict Dynamic Behavior of Sand Bulk Under 2D Vibration
Authors: Arjmandi Tash Hadi , Sadeghi Morteza , Ranjbaran Arash , Esmaeel Zadeh Esmaeel
Published: July 2009

2D motion pattern of an especial type of sand, which is used in lost-foam casting process, under the horizontal vibration investigated. Under this condition, the sand bulk in the experiment cell divides into 3 different zones, every one has its own property. Using dimensional analysis for the first time for this problem, dimensionless parameters which are useful to study sand bulk behavior, were identified. It observed that simple and linear relations exist among these parameters. They can be utilized in formulizing this phenomenon, by which motion pattern of sand bulk in various conditions can be predicted and optimum of geometric and vibration parameters for different purposes can be identified. The results not only are useful for this type of sand, but also may be extended to other types of granular materials too. The used method for detection what goes in the cell, without utilizing any external probe which may change the real conditions of the experiment cell, is another innovation of this study.
Experimental Investigation on Quenching Distance for Aluminum Dust Flames
Authors: Habibzadeh M. R. , Keyhani M. H.
Published: July 2009

An experimental investigation on quenching distance for Al dust flames have been done in improved flow system which can yield stable, controlled, and uniform dust mixtures. Experiments were performed with 18 micron aluminum particles diameter. Dust dispersion technique uses an annular high-speed jet which disperses dust continuously supplied via a piston-type dust feeding system. Laminarized dust flow ascending in a vertical Pyrex tube (d = 4.6cm, L = 150cm) was ignited at the open tube end. Constant pressure flames propagating downwards were observed. A set of thin, evenly spaced steel plates was installed in the upper third part of the tube in order to determine the flame quenching distance. Three different stages of flame propagation were observed: laminar, oscillating (transition region), and turbulent accelerating flames. Quenching distance as a function of dust concentration were determined during the laminar stage of flame propagation in dust-21% Oxygen-79% Nitrogen, dust-30% Oxygen-70% Nitrogen, and in dust-21% Oxygen-79% Argon mixtures. Furthermore, this research studies the effects of bed-gas on quenching distance and lean limit of combustion. It was found that the minimum quenching distance decreases when concentration of oxygen increases in the mixture. The minimum quenching distance is found to be about 4mm in air and decreases to 2mm in mixture of 30% O2. Also, it was found that the amount of lean limit of combustion decreases with increasing of oxygen percentage in mixture. The substitution of Argon for Nitrogen in air decreases the minimum quenching distance from about 4 to 3mm, and the amount of lean limit of combustion increases. The results is discussed with a mechanism of diffusive oxygen transport to the surface of burning Al particles in which a higher rate of oxygen transport in the N2/O2, as compared to the Ar/O2 gas mixtures.
Bubble Formation in a Large Scale System
Authors: Leishear Robert A. , Restivo Michael L. , Sherwood David J.
Published: July 2009

The complexities of bubble formation in liquids increase as the system size increases, and a photographic study is presented here to provide some insight into the dynamics of bubble formation for large systems. Air was injected at the bottom of a 28 feet tall by 30 inch diameter column. Different fluids were subjected to different air flow rates at different fluid depths. The fluids were water and non-Newtonian, Bingham plastic fluids, which have yield stresses requiring an applied force to initiate movement, or shearing, of the fluid. Tests showed that bubble formation was significantly different in the two types of fluids. In water, a field of bubbles was formed, which consisted of numerous, distributed, 1/4 to 3/8 inch diameter bubbles. In the Bingham fluid, large bubbles of 6 to 12 inches in diameter were formed, which depended on the air flow rate. This paper provides comprehensive photographic results related to bubble formation in these fluids.
Development of Three-Dimensional Particle Tracking Velocimetry for the Investigation of Unsteady Flows
Authors: Homeniuk D. , Nobes D. S. , Wilson D.
Published: July 2009

Instantaneous characterization of the three components of velocity of a fluid flow in a three-dimensional volume is difficult to accomplish under a variety of conditions. Symmetrical flows exhibit a measure of symmetry, which allow the use of a planar method. A method such as stereo particle imaging velocimetry could be used, which obtains three components of velocity in a planar sheet of the fluid. Flow asymmetries however, force the use of a fully three-dimensional approach to achieve a good understanding of the phenomenon. Particle tracking velocimetry is a method that allows three-dimensional information to be gathered instantaneously by determining the trajectories of individual particles. Limits exist, however, on this type of approach. This work examines the limits of a particle tracking velocimetry system that uses only two cameras to interrogate the flow.
Analysis of Inner Flow Inside Francis Turbine Runner Based on Dissipation Function
Authors: Wu Xiaojing , Wu Yulin , Liu Shuhong
Published: July 2009

Energy loss inside a Francis turbine runner is analyzed with dissipation function in this paper. The dissipation rate of a Newtonian flow with constant shear viscous has three constituents from dilation, vorticity, and surface strain, which is derived from kinetic energy equation presented in this paper. A commercial N-S equation solver has been employed for 3D turbulent flow simulation with a model Francis turbine, and three different operating conditions are chosen for comparison, which are part load, rated load, and excessive load. The results from simulation have been compared with model experiments to validate their preciseness and reliability. The distribution of dissipation constituents on runner blade surface have been extracted from the above simulation results. The distinction of these constituents can be used to identify flow structures inside runner. The flow energy loss is determined by dissipation function, thus it can affect the hydraulic efficiency of turbine runner. From the above results, it can be seen that what causes the energy loss, which is the dominant factor, and where it has the highest value. Thus this analysis based on dissipation function can be used for flow diagnosis inside the blade channel, and tell us which part of the blade should be improved to reduce the energy loss.
Analysis and Modelling of a Fluidic Actuator
Authors: Braud Caroline , Dyment Arthur , Kostas Jim , Foucaut Jean Marc , Stanislas Michel
Published: July 2009

This paper deals with the fluidic actuators in the pulsed mode used in turbulent boundary layer control, in particular as vortex generator (VG) in order to delay separation. Recently the study by Kostas et al (2007) has shown the importance of the transient phase of the VG actuators. In particular, an enhancement of the vortex-generation mechanism has been observed during the transient period, that is responsible for an increase of turbulence stress levels up to 200% relatively to the non actuated case. A large dependency of the exit velocity on the physical characteristic of the feed tube has been detected. This dependency suggests that a precise quantification of the pulsed jet dynamic during the transient period is necessary. In this work the transient behavior of the fluidic actuators used by Kostas et al (2007) is analyzed and experimented. A model is developed to explain the dynamics of the flow inside the actuator. On the whole, experiments show that the role of all physical parameters is consistent with the foreseen properties. The results obtained help to separate the input dynamic of the controller from the controlled flow. Another perspective of this work is to provide a guide for the design of fluidic actuators.
Development and Characterization of High Bandwidth Micro-Actuator
Authors: Solomon John T. , Kumar Rajan , Alvi Farrukh S.
Published: July 2009

This paper describes an experimental study conducted at the Advanced Aero Propulsion Laboratory (AAPL) on the design and development of actuator systems capable of producing high bandwidth, high momentum microjet arrays for active flow control applications. Using a simple geometry of a cavity with arrays of micro nozzles at the bottom end along with a primary source jet, highly unsteady microjets were produced in a frequency range of 6–60 kHz. The unsteady microjets, which are supersonic, have a mean velocity in the range of 300–400 m/sec with an unsteady component between 50–100 m/sec. Such actuators show considerable promise for flow control applications, especially in the supersonic domain. Notable characteristics of this design are its simplicity and the flexibility in controlling the frequency and amplitude suitable for the application of interest. The influence of feedback loop driven shear layer instability and other possible resonant mechanisms on the micro-actuator frequency response are outlined in the present paper. The location of cavity orifice within the Region of Instability (ROI), which is found to be the pressure recovery region of first shock cell of the source jet, plays a very important role in the output frequency and amplitude of the actuator. The length of the actuator cavity is another parameter that strongly influences the frequency of the actuator output. By using high resolution Micro-Schlieren images it was found that the frequency variation with Nozzle Pressure Ratio (NPR) is related to the shock cell properties of primary jet. As a result of this study, we have a better understanding of the geometric and flow parameters governing the unsteady properties of the actuator flow; an understanding that will be used to specifically tailor actuator design for various applications.
Investigation of Two-Phase Flow in Rectangular Micro-Channels
Authors: Kim Namwon , Evans Estelle T. , Soper Steven A. , Murphy Michael C. , Nikitopoulos Dimitris E.
Published: July 2009

This study addresses air-water, two-phase flows in micro-channels fabricated on poly-methyl-methacrylate (PMMA) with walls that are partially non-wetting (typical static contact angle 65° in stock form) and not molecularly smooth. Two different types of chips were prepared: Micro-milled micro-channels of aspect ratios 1, 2 and 3 with fixed hydraulic diameter on PMMA and micro-channels of unity aspect ratio replicated using hot embossing of PMMA with a micro-milled brass mold insert. Flow-maps obtained using the same gas-liquid injection geometry and method for the three aspect ratio micro-channels are presented, and regime boundaries are compared with those found by other investigations. The results indicate that the bubbly flow regime boundary is shifted to higher liquid and/or lower gas superficial velocities for the higher aspect ratio channels, while transition to the Annular and Annular-Dry regimes remains the same to within experimental uncertainty. The emphasis of what is presented is on the Segmented flow regime. Regular and irregular Segmented flow regimes of three types are assessed on the basis of the statistical variation in the associated phase length scales from flow observations over a substantial channel length. Comparison between results of the two different injection geometries and micro-channel manufacturing techniques indicate that feedback effects are a significant but not the only cause of segmented flow irregularity. The variability in the size of the liquid plug separating gas bubbles in Segmented flow is found to be substantially higher than that of the bubbles even when the flow is regular (low variability of bubble size). The average bubble length associated with a part of Segmented flows, regular and irregular alike is shown to scale approximately with the capillary number to the 2/3 power (liquid volumetric flow ratio to the −2/3). Irregular Segmented flow is favored by higher liquid superficial velocities, lower liquid volumetric flow ratios and lower channel aspect ratios. Of the three aspect ratios examined, the microchannel with aspect-ratio 3 displayed the broadest window of regular Segmented flow. Two-phase flow pressure drop was measured for test channels of unity aspect ratio. Each flow regime identified on the basis of topological observations is associated with different trends of the pressure drop variation with respect to volumetric flow ratio.
Effect of Gas-Liquid Ratio on Droplets Centricity and Velocity of an Effervescent Atomizer
Authors: Ghaemi S. , Nobes D. S. , Rahimi P.
Published: July 2009

Effervescent atomization is a twin fluid atomization mechanism which is based on the injection of gas into a liquid stream at an upstream location of the exit nozzle. This atomization mechanism is capable of producing droplets with Sauter Mean Diameter (SMD) comparable to other types of atomizers but at lower injection pressures. For the conditions investigated in this paper, liquid at the nozzle exit is an annular film surrounding the gas phase. A shadowgraph system is used to visualize particles shape and study droplets evolution in the spray field. Measurement of droplet SMD and centricity has been conducted at several axial and radial locations for different Gas-Liquid Ratios (GLRs). The shadowgraphy images reveal some non-spherical droplets which consist of both elliptical and coalescing droplets. Results also demonstrate that higher numbers of non-spherical droplets are observed at the near nozzle region and at higher liquid flow rate. In this work, spatial structure of the liquid phase velocity field has also been studied using a StereoPIV technique. The velocity field from StereoPIV measurements has been compared with the shadowgraphy velocity results averaged over different droplet size classes. This comparison has been conducted for the atomizer operating at different GLRs. Comparison of the results demonstrates that at the far-field, StereoPIV velocity field measurement is biased toward the velocity of droplets size classes which have relatively higher probability.
Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury
Authors: Wendel Mark , Felde David , Riemer Bernard , West David , D’Urso Brian , Ibrahim Ashraf
Published: July 2009

The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering the beam “window”, through which the high-energy proton beam passes, with a protective layer of gas. The difficulty lies in establishing a stable gas/liquid interface that is oriented vertically with the window and holds up to the strong buoyancy force and the turbulent mercury flow field. Three approaches to establishing the gas wall have been investigated in isothermal mercury/gas testing on a prototypical geometry and flow: (1) free gas layer approach, (2) porous wall approach, and (3) surface-modified approach. The latter two of these approaches show success in that a stabilized gas layer is produced. Both of these successful approaches capitalize on the high surface energy of liquid mercury by increasing the surface area of the solid wall, thus increasing gas hold up at the wall. In this paper, a summary of these experiments and findings is presented as well as a description of the path forward toward incorporating the stabilized gas layer approach into a feasible gas/mercury SNS target design.
Identification and Analysis of Vortical Structures in a Ribbed Channel
Authors: Wang Lei , Salewski Mirko , Sunde´n Bengt
Published: July 2009

Vortical motions, usually called sinews and muscles of fluid motions, constitute important features of turbulent flows and form the base for large-scale transport processes. In this study, we present a variety of flow decomposition techniques to identify and analyze the vortical structures in a ribbed channel. To this end, the instantaneous velocity fields are measured by means of a two-dimensional particle image velocimetry (PIV). Firstly, the implementation of Galilean-, Reynolds- and large-eddy simulation (LES) decompositions on the instantaneous flow fields allows one to perceive the coherent vortices embedded in the separated shear layer. In addition, the proper orthogonal decomposition (POD) is employed to extract the underlying flow features out of the fluctuating velocity and vorticity fields, respectively. For velocity-based decomposition, the first two POD modes show that the shear layer is highly unstable and associated with the ‘flapping’ motion. For vorticity-based decomposition, the first two POD modes are characterized by the distinct horizontal bands which manifest the coherent structures in the shear layer. In order to interpret the flow structures in a convenient way, a linear combination of POD modes (reconstruction) is also carried out in the present study. The result shows that a large-scale, pronounced vortex is recognizable in the region downstream of rib.
An Inverse Approach to Magnetorheological Damper Design: Hershel-Bulkley Model
Authors: Letelier Mario F. , Stockle Juan S. , Siginer Dennis A.
Published: July 2009

Magnetorheological fluids (MRF) are increasingly used for the design of dampers in many cases when a given response is critical for desired performance. Some recent examples are self-powered magnetorheological dampers, cable vibration control and wheeled vehicle dampers. Loads of this type can be very big, especially in the case of seismic-dampers as well as in heavy vehicles and aircraft landing gear. This problem can be more efficiently dealt with by using an inverse-problem strategy, where the required performance is specified a priori, and the fluid parameters are changed accordingly by means of a variable magnetic field. The effect on the flow of the time-variation of the parameters of the Herschel-Bulkley constitutive model is analyzed in this paper. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered, and the case where the yield stress and viscosity oscillate in time is explored in detail. The characteristics of the velocity field are analyzed for different values of the constants that determine the time structure of the constitutive parameters.
Numerical Experiments With Solid Handling Pumps
Authors: Jogiya Hitesh , Kshirsagar J. T.
Published: July 2009

Solid handling pumps are used in Sewage applications, Slurry transportation, transportation of floating solids etc. Many manufacturers supply such solid handling pumps for different applications. Few of the manufactures have test facility to study the impact of solid particles on overall performance of pump. It is then possible to experimentally bring out effect of solid size, its concentration etc. on overall performance. The literature is available for several such tests conducted by pump manufacturers. In absence of experimental test facility for solid handling pumps, a numerical approach was proposed to investigate the effect of solid particles on the pump performance. Commercially available CFD tool was used to carry out numerical experiments. A standard pump in production was chosen as a test case. It was ensured that experimental test results of similar size pump are available in literature. The work presented here is the extension of the work done by Gupta Amit for a solid handling impeller [8]. The similar impeller assembled with casing for solid handling pump was analyzed first to compute the performance of whole pump with clear water. This was compared with test results available from factory tests conducted experimentally with clear water. The same geometry was then analyzed using particle tracking drag models available in the software given the new boundary conditions of solid additions. Results from the numerical experiments, including effect of particle size, their concentrations etc were brought out. The particle trajectory from impeller entry to exit of casing gave idea as how particles travel in solid handing pumps. The computational results were compared with the ones presented in the Pump Handbook by Karassik. The software results were useful in getting additional information on loss in impeller and casing separately. This gives a clue to as which component needs improvement. The paper describes the approach used in numerical experiments and the results thereof.
Numerical Analysis of Geometric Effects on Pressure Drop in 180° Turning Channels
Authors: Spivey Sean , Shollenberger Kim A.
Published: July 2009

A numerical investigation of geometric effects on pressure loss around 180° turning channels in a cooled turbine blade has been conducted. A base case was created for validation and to determine the optimum grid density, inlet boundary conditions, and turbulence model. For the base case, the channel maintains constant square cross-section geometry in both the inlet and outlet leg. After establishing the optimum criteria for the base case, the geometry of the outlet leg is altered from the standard square cross-section four ways. Two of the four altered geometries hold a constant area ratio, while the decline angles are changed to 6° and 12°. The final two geometries hold a constant decline angle of 6° while the area ratios are increased and decreased 20%. Using the optimum criteria found for the base case, models are run with the new geometries. As the angle of decline is increased the total pressure loss decreases slightly, while velocity magnitude plots indicate poor heat transfer characteristics near the inner wall due to flow separation. As the area ratio increases, total pressure loss decreases and velocity magnitude plots again indicate poor heat transfer characteristics. Thus, the geometry can effect the pressure loss by as much as 10%.
A Model for Analyzing Flow Transients in a Single Closed Loop
Authors: Givi Behrang Sadeghi
Published: July 2009

A mathematical model is developed upon which the velocity of flow during a centrifugal pump failure transient is determined analytically without the use of pump characteristics’ curves. The influence of the two most important parameters, kinetic energy in the piping system and kinetic energy of the pump, are considered in the form of a ratio called hereafter an effective energy ratio. The results show that the effect of a mechanical friction loss on the flow rate is very small in the early stage of pump failure transient, and the time of two-third decay of the flow is not affected very much by the friction loss. However, this effect is larger in the later stage of the flow decay. Therefore the time when the flow rate becomes zero, depends very much on the estimation of this loss. Good agreement is noted when the results of the analytical method are compared with those obtained by the use of experimental characteristics’ curves. The model is also used to analyze the transient during a fast startup. Also further comparison of the analytical model with the collected flow transient experimental data show a very good agreement.
A Study of the Effect of Blade Count on Efficiency Using 3D CFD for High Pressure Steam Turbines
Authors: Cheon J. H. , Lee K. J. , Park J. J. , Kim J. H. , Ha M. Y.
Published: July 2009

The selection of stationary blade count for a steam turbine is closely related to efficiency and manufacturing costs. In this study, the effect of blade count on blade efficiency was examined by CFD analysis. The analyzed model is the steam path of a single stage, including stationary and moving blades to understand thermodynamic and aerodynamic phenomenon of the interstage section. Three cases with 40, 60 and 80 stationary blades and 56 moving blades were used as steam path models. These blades were designed by the in-house systems with free vortex concept for a high pressure turbine. It was shown that the throat area of the stationary blades induced by the variation of blade count affects velocity coefficient (Cv) and flow coefficient (Cq). The mass flow averaged Cv and Cq by 3-dimensional CFD analysis, which considers end wall loss, were calculated. From this result, averaged Cv and Cq tended to decrease as the count of stationary blade increased. This tendency was due to stagnation pressure loss distribution. According to analyses of profile loss and end wall loss, it was confirmed that profile loss decreased as blade count decreased, whereas end wall loss increased but was insignificant compared to profile loss.
Minimum Fluidization Velocity and Gas Holdup in Fluidized Beds With Side Port Air Injection
Authors: Franka Nathan P. , Drake Joshua B. , Heindel Theodore J.
Published: July 2009

Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 cm and 15.2 cm diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Time-averaged local and global gas holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local gas holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.