bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study of Turbulent Flows Through a Circular Duct With a Rotating Fan
Authors: Rajwade Gaurav , Cui Jie
Published: July 2010

A fan is an important part for air circulation in household appliances and automobiles. In this research an attempt has been made to extract the flow information using the Computational Fluid Dynamics (CFD) technique. The numerical results were found for a case with a stationary fan inside the duct and the data obtained were in good agreement with the experiment. The evolution of velocity profiles at various axial locations for different flow conditions were also studied in this research. The numerical method was then extended to the cases with a rotating fan. A proof-of-concept run was also successfully carried out to showe the relationship between air flow rate in the duct and the corresponding pressure rise.
Natural Convection in an Air-Filled Cubical Enclosure With a Protruding Heat Sink: Application to a Thermoelectric Refrigerator
Authors: Botello-Arredondo Israel , Hernandez-Guerrero Abel , Pen˜a-Taveras Marino , Miranda-Razo Victor , Rubio-Arana Cuauhtemoc
Published: July 2010

The present study evaluates the effects of a protruding heat sink located on one of the vertical walls of a cubic cavity, with a free convective laminar regimen. The best of three locations for the heat sink will be determined with the analysis of the velocity and temperature fields in the cavity. An optimal operation condition is required since the cavity will contain medical products with a specific temperature range. Three different locations for the heat sink, (in the +Y direction), are to be studied: 1/3 H, 1/2 H and 2/3 H, where H is the height of the cavity, for different values of Rayleigh Number 103<Ra<106. The heat exchange occurs between the heat sink and the isothermal walls. The results obtained show that it is recommended to place the heat sink at the position H/2. This configuration presented the best behavior of the fluid, dynamically and thermally. The results will be used for a further and more completed numerical analysis, and to determine the thermoelectric refrigerator parameters for a later experimental study with a prototype.
An Extended Analytical and Numerical Design Method With Applications of Radial Fans
Authors: Epple Philipp , Miclea Mihai , Luschmann Christian , Ilic Caslav , Delgado Antonio
Published: July 2010

The use of high speed radial impellers is very common in fans for industrial application. It is very common also to manufacture the radial impellers for these fans with circular arc blades. The design process is also almost always based on former impeller series and experimental data available. In this work a method is presented to improve the efficiency of radial impellers with a combined analytical and numerical method. This method is based on a new extended analytical formulation of the flow in radial impellers allowing optimizing efficiency in design stage. The blade shapes are computed with an inverse method. The design is then validated by means of CFD computation. Finally a prototype was built and measurements were carried out in a test rig. It is shown also that the design method delivered very good predictions leading to an efficiency increase of 13% of efficiency and a maximum flow rate increase of 11% absolute. The design point was also met. It is also shown that the numerical computations and measurements are in good agreement. An analysis of the CFD results is also presented, giving insight in the substantial flow information inside the old and the new impeller. The method presented is a combined analytical and numerical method suited to design high efficiency radial impellers without the need of a previous impeller series or knowledge of experimental data.
A Finite Element Based Perturbation Method for Nonlinear Free Vibration of Composite Cylindrical Shells
Authors: Rahman T. , Jansen E. L. , Tiso P.
Published: July 2010

In this paper a finite element based perturbation approach for nonlinear vibrations is presented that is applicable to shell structures with an arbitrary geometry. The approach is based on a perturbation method to approximate the frequency-amplitude relation in the nonlinear vibration analysis of general structures with an arbitrary geometry. The method is formulated using a functional notation, and is subsequently converted to a finite element notation. After the determination of the linear natural frequency and corresponding vibration mode, the perturbation approach yields the initial curvature of the frequency-amplitude relation with a modest additional computational cost. The perturbation approach has been implemented in a general purpose finite element code and applied in the finite element analysis of the nonlinear vibration behavior of composite cylindrical shells using a curved shell element. The finite element implementation of the approach for composite shells is described. Results for composite cylindrical shells are presented and compared with results obtained via semi-analytical methods published earlier by the second author.
Advanced Thermodynamics Applications Using Mathcad
Authors: McClain Stephen T.
Published: July 2010

Mathcad thermodynamic property function sets have been developed for many engineering fluids. In past publications, which introduced the property function sets, examples were provided that demonstrated the usefulness of the functions in solving typical homework problems for either an Introduction to Thermodynamics or an Applied Thermodynamics course. The capabilities of Mathcad allow for much more complicated analyses than are typically discussed in undergraduate engineering thermodynamics courses. Specifically, Mathcad’s abilities 1) to perform calculations on multi-dimensional arrays, 2) to optimize functions using modified Newton-Raphson techniques, 3) to read text-file data sets, and 4) solve systems of non-linear equations, enables the analysis of very complex thermodynamic problems. Examples are provided to demonstrate the very robust capabilities of Mathcad using previously developed thermodynamic property function sets. The examples discussed include the optimization of a steam power cycle using two feedwater heaters, the analysis of gas turbine data acquired from a small turbojet apparatus, and the analysis of evaporator flooding on the performance of an industrial refigeration system. The analyses and figures produced in Mathcad demonstrate its effectiveness for complex thermodynamic calculations and for providing insight into the performance of complex thermodynamic systems.
Numerical Study of Evaporation Heat Transfer From the Liquid-Vapor Interface in Wick Microstructures
Authors: Ranjan Ram , Murthy Jayathi Y. , Garimella Suresh V.
Published: July 2010

A numerical model of the evaporating liquid meniscus under saturated vapor conditions in wick microstructures has been developed. Four different wick geometries representing the common wicks used in heat pipes, viz., wire mesh, rectangular grooves, sintered wicks and vertical microwires, are modeled and compared for evaporative performance. The solid-liquid combination considered is copper-water. Steady evaporation is modeled and the liquid-vapor interface shape is assumed to be static during evaporation. Liquid-vapor interface shapes in different geometries are obtained by solving the Young-Laplace equation using Surface Evolver. Mass, momentum and energy equations are solved numerically in the liquid domain, with the vapor assumed to be saturated. Evaporation at the interface is modeled by using appropriate heat and mass transfer rates obtained from kinetic theory. Thermo-capillary convection due to non-isothermal conditions at the interface is modeled for all geometries and its role in heat transfer enhancement from the interface is quantified for both low and high superheats. More than 80% of the evaporation heat transfer is noted to occur from the thin-film region of the liquid meniscus. Very small Capillary and Weber numbers arising due to small fluid velocities near the interface for low superheats validate the assumption of static liquid meniscus shape during evaporation. Solid-liquid contact angle, wick porosity, solid-vapor superheat and liquid level in the wick pore are varied to study their effects on evaporation from the liquid meniscus.
Dynamic Behavior of Electronic Module Spring Clips, Retention Bar, and Backplane Connector: Modeling and Testing
Authors: Vandevoordt Kenneth P. , Feng Michael
Published: July 2010

Electronic modules for a guidance system are mounted in a rack with spring clips resisting motion normal to the printed wiring board (PWB) and an aluminum bar with an elastomer pad keeping the module connected to a backplane. The elastomer pad also resists motion normal to the board. The proper boundary conditions for the spring clips, retention bar, and connector are needed in a finite element model in order to evaluate the shock and vibration transmitted to the module’s electrical components. The finite element model of the module was assembled, and an actual module was tested under random vibration and a 1g sine sweep. The printed wiring board elastic modulus was artificially set higher in the FEM than a measured value to account for the stiffening effect of board components which were omitted from the model. By also choosing the proper boundary conditions to represent the spring clips, retention bars, and backplane connection, the finite element model was able to match the first and second mode frequencies from the hardware test results.
Human-Hybrid Powered Vehicle (H2PV) Using an Oscillating Drive
Authors: Bronson Henry D. , Pal Rahuljit
Published: July 2010

For more than a century, bicycle designs have used single chain drive transmissions in the belief that no other option exists. An alternative to a chain driven system is an endless belt transmission system using all three distinct belt forms; flat, V, and toothed. In the described transmission the belt acts as a combination flat and V-belt on the drive pulley, and like a timing belt on the driven pulley. Uniquely, the belt teeth have an asymmetric, pawl like tooth profile. This permits safe operation in conditions when the driven pulley circumference is already moving faster than the drive belt teeth, a common occurrence during bicycle or scooter coasting. The material memory of the elastomeric belt acts to bias the drive to disengagement, yet the belt and drive pulley are light. Combined with carefully positioned back idlers, the mere initiation of a power stroke quickly engages the transmission automatically. One major application described here is a reciprocating drive actuated with natural leg action that is easily augmented with power assistance, producing a Human-Hybrid Powered Vehicle (H2PV). A model demonstrates significant weight reduction versus chain and sprocket drives, along with the elimination of an overrunning clutch or free-wheel, clean and quiet operation, weight efficient design, and use of modern lightweight materials like thermo-plastic plastics, glass, carbon or aramid fibers, and thermo-set plastics (polyurethanes).
Analytical Conditions for Motion Complexity of a 2-DOF Friction-Induced Oscillator Moving on Two Oscillators
Authors: Luo Albert C. J. , Wang Yang
Published: July 2010

In this paper, the analytical conditions for stick and nonstick motions are discussed in 2-DOF friction induced oscillator moving on two oscillators. From physical points of view, the physical problem is stated. In order to develop the analytical conditions for stick and non-stick motion, the absolute and relative descriptions are given for a better understanding of the complex motions in such a 2-DOF oscillator interacting with two individual oscillators through dry friction. The analytical conditions are sketched intuitively.
On Stable and Unstable Periodic Solutions of N-Dimensional Discrete Dynamical Systems
Authors: Luo Albert C. J. , Guo Yu
Published: July 2010

This paper presents a methodology to analytically predict the stable and unstable periodic solutions for n-dimensional discrete dynamical systems. The positive and negative iterative mappings of discrete maps are introduced for the mapping structure of the periodic solutions. The complete bifurcation and stability of the stable and unstable periodic solutions relative to the positive and negative mapping structures are presented. A discrete dynamical system with the Henon map is investigated as an example. The Poincare mapping sections relative to the Neimark bifurcation of periodic solutions are presented, and the chaotic layers for the discrete system with the Henon map are observed.
Sensitivity of Solder Joint Fatigue to Sources of Variation in Advanced Vehicular Power Electronics Cooling
Authors: Vlahinos Andreas , O’Keefe Michael
Published: July 2010

This paper demonstrates a methodology for taking variation into account in the thermal and fatigue analyses of the die attach for an inverter of an electric traction drive vehicle. This method can be used to understand how variation and mission profile affect parameters of interest in a design. Three parameters are varied to represent manufacturing, material, and loading variation: solder joint voiding, aluminum nitride substrate thermal conductivity, and heat generation at the integrated gate bipolar transistor, or IGBT. The influence of these parameters on temperature and solder fatigue life is presented. The heat generation loading variation shows the largest influence on the results for the assumptions used in this problem setup.
An RBF Interpolated Generalized Finite Difference Meshless Method for Compressible Turbulent Flows
Authors: Erhart Kevin J. , Gerace Salvadore A. , Divo Eduardo A. , Kassab Alain J.
Published: July 2010

Computational Fluid Dynamics (CFD) is a topic that has been researched heavily over the past 50 years, especially since the accessibility to sufficient computational resources has greatly increased. However, it is precisely this increase in technology that has led to a lack of efficiency in many CFD developments, especially when it comes to the process of grid generation. While many researchers are currently focused on solutions to the grid generation problems of traditional CFD techniques, the majority of these approaches still suffer serious numerical difficulties due to the underlying CFD solution algorithms that are used. Therefore, the focus of this work is to demonstrate a novel approach to true CFD automation which is based on traditional Cartesian grid generation coupled with a Meshless flow solution algorithm. As Meshless method solutions require only an underlying nodal distribution, this approach works well even for complex flow geometries. And with the addition of a so-called shadow layer of body-fitted nodes, the stair-casing issues of typical Cartesian solvers are eliminated. This paper will describe the approach taken to automatically generate the Meshless nodal distribution, along with the details of an automatic local refinement process. Also, as the primary interest of automated CFD is for aerospace applications, this work includes the development of standard two-equation turbulence models for use in this Meshless based solver. Finally, results will be shown for the application of high-speed, compressible turbulent flows.
Design of a Hydrogen Fuel Cell Vehicle in the Capstone Design Course
Authors: Slate Sean , Fuini Mathew , Rose Damion , Kutterer Alexander , Patton Brandon , Cox Windell , Saad Messiha
Published: July 2010

The capstone course in Mechanical engineering at North Carolina A&T State University (NCA&TSU) is divided into two semesters. Team design projects begin in the fall semester and continued during the following spring semester. North Carolina State University, we, like virtually all other engineering programs, require a capstone course involving a major design project. This year a team of four mechanical engineering students and two electrical engineering students has decided to design and build a fuel efficient hydrogen fuel cell vehicle to compete in the 2009 Shell Eco-Marathon. The competition is designed to provide engineering students with a real life design experience. The objective of the competition is to encourage innovation and foster the development of sustainable mobility. Participants can design a vehicle for the Prototype Group or the Urban Concept Group. The Prototype Group allows maximum technical creativity, while imposing minimum design restrictions. The Urban Concept Group is closer to actual road going vehicles and addresses current transportation requirements. Both groups must meet the design criteria and meet safety standards provided by the 2009 Shell Eco-Marathon Official Rules. Participants must also select from a list of Shell approved energy sources to power their vehicles. The list includes both traditional fuels and alternative fuels. The main objective of the competition is maximum fuel efficiency. This year NCA&T Shell Eco-Marathon team has decided to enter the Prototype Group and has selected Hydrogen as the energy source. Our team placed in the third place in the hydrogen fuel cell prototype group. The completion of the Shell Eco-Marathon design project will serves as a valuable learning experience, while demonstrating the technical abilities of the students.
Interaction Effect of Voids and Standoff Height on Thermo-Mechanical Durability of BGA Solder Joints
Authors: Ladani Leila J. , Razmi Jafar
Published: July 2010

This paper documents simulation studies on interactive effect of standoff height and void volume on thermo-mechanical durability of Ball Grid Array (BGA) solder joints using a 3D visco-plastic finite element analysis. SE software was used to find the optimized shape of the solder joints and standoff height by minimizing the surface energy as voids with different sizes were placed in solder balls. A global-local modeling approach was then utilized to model thermo-mechanical durability of voided solder joints. Void area fraction ranges of 14% to 40% were analyzed. A nonmonotonic behavior of durability versus void area fraction was observed. The results showed that if the void is completely inside the solder ball and has no interface with the boundaries of the joint, it does not have a detrimental effect and even improves the durability as the void size increases. However, voids located at the interface of solder joint and copper pads were found very detrimental to durability. Factors such as load bearing area, stress concentration factor and overall compliance of the structure were found responsible for the non-monotonic behavior of the joints. An analytical micro-mechanics approach was used to calculate the compliance of the structure and a nonmonotonic trend in phase with the durability trend was observed. The stress concentration factor also showed the same non monotonic trend. Rise of these two factors for the void interfacing with copper pads in addition to the decreased load bearing area effect resulted in drastic decrease in durability.
A Module-Based Approach for FEM Learning in Engineering Education
Authors: Xin X. J. , Cai Liang-Wu , Yoder Bradley , Chattopadhyay Arka , Panthaki Malcolm
Published: July 2010

The finite element method (FEM) has become an indispensable tool for design, analysis, and modeling in a vast array of engineering and applied science disciplines. Despite its importance, however, FEM is typically not a required undergraduate course. In this work, a module-based approach is promoted for introducing FEM applications into undergraduate engineering courses without the need for a major revision of the course content or the existing curricula. A Learning Module (LM) is defined as a well-structured, compact, and self-sufficient learning resource that provides a learner the required content in a precise and concise manner, enabling the learner to learn efficiently and effectively. The organization and essential components of an FEM learning module are discussed in detail. Critical to the construction of a learning module is the principle of conceptual analysis which allows the extraction of general concepts, principles, and procedures from FEM software dependent specifics. The application of conceptual analysis throughout the development of learning modules is demonstrated and discussed. The pedagogical foundations behind the module-based learning are explored from the cognitive science perspective, and implications of module-based learning in undergraduate education are discussed.
Processing Analysis of the Ternary LiNH2-MgH2-LiBH4 System for Hydrogen Storage
Authors: Niemann Michael U. , Srinivasan Sesha S. , Kumar Ashok , Stefanakos Elias K. , Goswami D. Yogi , McGrath Kimberly
Published: July 2010

The ternary LiNH2-MgH2-LiBH4 hydrogen storage system has been extensively studied by adopting various processing reaction pathways. The stoichiometric ratio of LiNH2:MgH2:LiBH4 is kept constant with a 2:1:1 molar ratio. All samples are prepared using solid-state mechano-chemical synthesis with a constant rotational speed, but with varying milling duration. All samples are intimate mixtures of Li-B-N-H and MgH2, with varying particle sizes. It is found that the samples with MgH2 particle sizes of approximately 10nm exhibit lower initial hydrogen release at a temperature of 150°C. The as-synthesized hydrides exhibit two main hydrogen release temperatures, one around 160°C and the other around 300°C. The main hydrogen release temperature is reduced from 310°C to 270°C, while hydrogen is first reversibly released at temperatures as low as 150°C with a total hydrogen capacity of 6 wt.%.
Detection of Generalized Roughness on Ball Bearing by Cyclostationarity Technique
Authors: D’Elia Gianluca , Cocconcelli Marco , Rubini Riccardo
Published: July 2010

This paper deals with the detection of generalized roughness on ball bearing. In literature most of the authors focus on the detection of incipient single defects. In the early stage of the damage the vibration signal of the bearing contains characteristics components in the frequency spectrum that reveal both the presence of the fault, and on which element of the bearing the damage is placed. In time the damage develops and important parts of the bearing surface (usually the external or the internal rings) become faulted, and the bearing is said to be affected by generalized roughness. In that case the vibration level of the bearing increases and the characteristic frequencies of the damage are no longer recognizable. In this paper the authors propose the use of cyclostationarity to analyse the vibration signal in the generalized roughness condition. The cyclostationarity allows to detect phenomena which happens repeatedly in a signal. In particular the second-order cyclostationarity has been proved to be suitable for bearing diagnostics, since the periodic impact between a ball and a faulted ring happens with a variable period due to slippery between the bearing elements. So far the cyclo-stationarity has been used to detect single defects, in this paper its use is extended to distributed defects. Experimental results are reported. In particular a degreased bearing is placed on a test-rig and radially loaded to accelerate wear phenomena. The vibration signal is then analysed with two techniques compared to each other: the envelope analysis (which is a well-known method taken from the literature) and cyclostationarity.
Direct Numerical Simulations of Magnetic Field Effects on Turbulent Duct Flows
Authors: Chaudhary R. , Vanka S. P. , Thomas B. G.
Published: July 2010

Magnetic fields are crucial in controlling flow in various physical processes of significance. One of these processes, which has significant application of a magnetic field, is continuous casting of steel, where different magnetic field configurations are used to control the turbulent steel flow in the mold to minimize defects in the cast steel. This study has been undertaken to analyze the effect of magnetic field on mean velocities and turbulence parameters in the molten metal flows through a square duct. Direct Numerical Simulations without using a sub-grid scale (SGS) model have been used to characterize the three-dimensional transient flow. The coupled Navier-Stokes-MHD equations have been solved with a three-dimensional fractional-step numerical procedure. Because liquid metals have low magnetic Reynolds number, the induced magnetic field has been neglected and the electric potential method for magnetic field-flow coupling has been implemented. Initially, laminar simulations in a square duct have been performed and results generated were compared with previous series solutions. Next, simulations of a non-MHD flow in a square duct at low Reynolds number were performed and satisfactorily compared with results of a previous DNS study. Subsequently, different levels of a magnetic field were applied to study its effect on the turbulence until the flow completely laminarized. Time-dependent and time-averaged flows have been studied through mean velocities and fluctuations, and power spectrums of instantaneous velocities.
Performance of a 1kW (16-Cell) High Temperature PEM Fuel Cell Stack Prototype: An Experimental Evaluation
Authors: Das Susanta K. , Reis Antonio , Berry K. Joel
Published: July 2010

In this study, we designed and built a 1 kW (16-cells) stack prototype of high temperature PEM fuel cell with 440cm2 active area of each individual cell. The purpose of this research is to experimentally study the performance of our newly built high temperature PEM fuel cell stack at different operating conditions and to judge the performance for possible commercialization aspects. The performance of the fuel cell stack in terms of current-voltage characteristics has been experimentally measured for each of the cells in the 16-cell stack (1kW). Experimental data of this type is required to develop and validate the fuel cell models to understand and optimize the operation of the stack and further stack design improvements. The fuel cell stack is fed with industry-grade (99.999%) pure hydrogen. The fuel cell stack was extensively tested at 145°C and the current-voltage characteristics were determined by varying the current loads. The results will be very helpful to understand the cell performance in terms of current-voltage characteristics of 1kW PEM fuel cell stack.
Hydrogen Sorption Behavior in Conducting Polymer Nanostructures
Authors: Niemann Michael U. , Srinivasan Sesha S. , Phani Ayala R. , Kumar Ashok , Goswami D. Yogi , Stefanakos Elias K.
Published: July 2010

Conducting polyaniline nanofibers were synthesized using chemical templating method followed by electrospun process. These nanofibers have been compared with their standard bulk counterpart and found to be stable up to 150°C. Polyaniline nanofibers prepared by electrospun method reveal high hydrogen uptake of 10wt.% at around 100°C in the first absorption run. However, in the consecutive hydrogenation and dehydrogenation cycles, the hydrogen capacity diminishes. This is most likely due to hydrogen loading into the polymer matrix, chemisorption and saturation effects. A reversible hydrogen storage capacity of ∼3–10 wt.% was also found in the new batch of electrospun nanofibers at different temperatures. The surface morphologies before and after hydrogen sorption of these PANI nanofibers encompass significant changes in the microstructure (nanofibrallar swelling effect) which clearly suggest effective hydrogen uptake and release.
Hole-Pattern Seals: A Three Dimensional CFD Approach for Computing Rotordynamic Coefficient and Leakage Characteristics
Authors: Untaroiu Alexandrina , Migliorini Patrick , Wood Houston G. , Allaire Paul E. , Kocur John A.
Published: July 2010

Labyrinth and other annular seals are commonly used in the turbomachinery industry to limit the leakage between different pressure regions. The pressure driven flow these seals experience can produce significant forces on the rotor. These fluid-induced excitation forces can exert a strong influence on the dynamic characteristics of the machine. Such seal forces can cause the rotor to become unstable, or when properly designed, stabilize a troublesome machine. Thus, it is important to accurately quantify the fluid-induced forces exerted on the rotor to effectively predict the dynamic behavior. Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient, due to the assumptions made to simplify the flow equations, seal bulk flow models lack accuracy when dealing with more complex geometry seals, such as hole-pattern seals. Unlike the bulk flow model, computational fluid dynamics (CFD) makes no simplifying assumption on the seal geometry, shear stress at the wall, relationship between wall shear stress and mean fluid velocity, or characterization of interfaces between control volumes. This paper presents a method to calculate the linearized rotordynamic coefficients for a hole-pattern seal by means of a three dimensional CFD approach to estimate the fluid-induced forces acting on the rotor. The system is modeled as a rigid rotor, with rotational speed, ω, and whirl frequency, Ω, describing non-synchronous whirl orbits around a static operating point. The Reynolds-averaged Navier-Stokes equations for fluid flow are solved by dividing the volume of fluid into a discrete number of points at which unknown variables (velocity, pressure, etc.) are computed. As a result, all the details of the flow field, including the fluid forces with potential destabilizing effects, are calculated. A 2nd order regression method is then utilized to express the fluid induced forces in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients.
Tracking Muscle Fatigue Markers Through Nonlinear and Multivariate Analysis of Motion Kinematics
Authors: Segala David B. , Chelidze David , Schiffman Jeffrey M. , Gates Deanna , Dingwell Jonathan
Published: July 2010

Both athletes and soldiers subject their body to extensive prolonged movements at the price of completing their tasks. The purpose of his study is to show that phase space warping (PSW) concept and smooth orthogonal decomposition (SOD) can be used to extract muscle fatigue related information from easily obtainable and noninvasive movement kinematics data. Two experimental setups are considered: load carrying soldiers walking on a treadmill and subjects performing a sawing motion. PSW and SOD based fatigue related trends are compared against local muscle fatigue markers obtained from surface electromyography (sEMG) measurements. In particular, a decrease in the mean power frequencies (MNF) or median power frequencies (MDF) of the sEMGs are used to indicate the onset of muscle fatigue, since a muscle fatigue causes a shift in the power spectrum of sEMG to lower frequencies.
Ghost Fluid Based Immersed Boundary Treatment for Lattice Boltzmann Method
Authors: Tiwari Arpit , Samala Rahul , Vanka S. P.
Published: July 2010

An immersed boundary method has been developed for Lattice Boltzmann Equations via ghost fluid approach. Image points of the ghost points inside the fluid domain are obtained by extrapolation along the boundary normal. Velocity, density and non-equilibrium value of the distribution function at ghost points are extrapolated from image point values which are calculated by interpolation from the boundary and fluid domain. The distribution function at ghost points is computed from the extrapolated non-equilibrium part and the equilibrium part which is obtained from extrapolated values of the velocities. The method is found to be second order accurate. The method is applied to concentric 2D Couette flow and 3D Taylor–Couette flow.
Experimental Simulation of Contaminant Deposition on a Film Cooled Turbine Airfoil Leading Edge
Authors: Albert Jason E. , Keefe Kelly J. , Bogard David G.
Published: July 2010

A significant challenge of utilizing coal-derived synthetic fuels for gas turbine engines is mitigating the adverse effects of fuel-born contaminant depositions on film cooled turbine surfaces. A new experimental technique has been developed that simulates the key physical, but not the chemical, aspects of coal ash deposition on film cooled turbine airfoil leading edges in order to better understand the interaction between film cooling and deposition and to produce improved film cooling designs. In this large-scale wind tunnel facility, the depositing contaminants were simulated by atomized molten wax droplets sized to match the Stokes numbers of coal ash particles in the engine conditions. The sticking mechanism of the molten contaminants to the turbine surfaces was simulated by ensuring the wax droplets remained somewhat molten when they arrived at the cooled model surface. The model and wax deposits had thermal conductivities such that they matched the Biot numbers of clean and fouled turbine airfoils at engine conditions. The behavior of the deposition growth was controlled by adjusting the mainstream, coolant, and wax solidification temperatures. Simulated depositions were created for a range of test durations, film cooling blowing ratios, and controlling temperatures. Inspection of the resulting depositions revealed aspects of the flow field that augment and suppress deposition. Deposition thickness was found to increase in time until a quasi-steady thickness was attained. Blowing ratio and the difference between mainstream and wax solidification temperatures strongly affected characteristics of the depositions. Model surface temperatures greatly reduced under the depositions as they developed.
A Computationally Efficient Planar Rigid Body Distance Metric
Authors: Schimmels Joseph M. , Criales Luis E.
Published: July 2010

A means of assessing the quality of a given rigid body configuration relative to a desired position and orientation is developed. Here, the assessment is based on the desired positions of all particles that constitute the body. This measure of quality has previously been shown to meet the mathematical requirements of a metric. This metric, however, has been largely dismissed in practical application due to the difficulty in performing its calculation. This paper describes procedures to efficiently calculate this metric for planar positioning problems. A method of obtaining an analytical formulation for planar displacement for any polygonal body is presented. An approximation function for the metric is also presented. This approximation function is very easily calculated and provides an intuitive appreciation of the metric values. Calculation times for the metric for standard polygonal body geometries is on the order of 100 microseconds on a laptop computer. Calculation times for the approximation function for standard polygonal bodies is on the order of microseconds.
The Effect of Catalyst Coated Diffusion Media on PEM Fuel Cell Performance
Authors: Fultz Derek W. , Chuang Po-Ya Abel
Published: July 2010

Two fuel cell architectures, differing only by the surfaces onto which the electrodes were applied, have been analyzed to determine the root causes of dissimilarities in performance. The basic proton exchange membrane fuel cell (PEMFC) is comprised of the proton transporting membrane, platinum-containing anode and cathode electrodes, porous carbon fiber gas diffusion media (GDM), and flow fields which deliver the reactant hydrogen and air flows. As no optimal cell design currently exists, there is a degree of latitude regarding component assembly and structure. Catalyst coated diffusion media (CCDM) refers to a cell architecture option where the electrode layers are coated on the GDM layers and then hot-pressed to the membrane. Catalyst coated membrane (CCM) refers to an architecture where the electrodes are transferred directly onto the membrane. A cell with CCDM architecture has tightly bonded interfaces throughout the assembly which can result in lower thermal and electrical contact resistances. Considering the fuel cell as a 1-D thermal system, the through-plane thermal resistance was observed to decrease by 5–10% when comparing CCDM to CCM architectures. This suggests the thermal contact resistance at the electrode interfaces was significantly reduced in the hot-press process. In addition, the electrical contact resistances between the electrode and GDM were observed to be significantly reduced with a CCDM architecture. This study shows that these effects, which have a potential to increase performance, can be attributed to the hot-press lamination process and use of CCDM architecture.
A Computationally Efficient Planar Rigid Body Velocity Measure
Authors: Criales Luis E. , Schimmels Joseph M.
Published: July 2010

A planar rigid body velocity measure based on the instantaneous velocity of all particles that constitute a rigid body is developed. This measure compares the motion of each particle to an “ideal”, but usually unobtainable, motion. This ideal motion is one that would carry each particle from its current position to its desired position on a straight-line path. Although the ideal motion is not a valid rigid body motion, this does not preclude its use as a reference standard in evaluating valid rigid body motions. The optimal instantaneous planar motions for general rigid bodies in translation and rotation are characterized. Results for an example planar positioning problem are presented.
Static Analysis of Fe Discretized Structures With Bounded Uncertainties via Interval Method
Authors: Impollonia Nicola , Muscolino Giuseppe
Published: July 2010

The uncertainty presents in many engineering analysis is usually modeled by probabilistic approach. It is now largely recognized that the probabilistic approach often cannot be applied to describe structural uncertainty; indeed, it requires a wealth of data, often unavailable, to define the probability density function of the uncertainties. Alternatively non-probabilistic method can be adopted. In this framework, the interval model seems today the most suitable analytical tool. The interval model is derived from the interval analysis, in which the number is treated as an interval variable with lower and upper bounds. However, the application of the interval analysis in classical form can result in a severe overestimation of the uncertainty of the output. In this paper the limit of interval analysis is overcome by deriving an alternative solution, in the framework of linear static analysis of finite element modeled structures with uncertain-but-bounded parameters. The proposed procedure is based on the factorization of the elemental stiffness matrix following the unimodal components concept, which allows a non conventional assembly of the global stiffness matrix, and on the inversion of the assembled stiffness matrix by an interval-valued Sherman-Morrison formula. Numerical results on truss structures evidence the great accuracy of the proposed approach.
Power Generation and Heat Recovery Model of Reciprocating Internal Combustion Engines for CHP Applications
Authors: Cho Heejin , Luck Rogelio , Chamra Louay M.
Published: July 2010

This paper presents a power generation and heat recovery model for reciprocating internal combustion engines (ICEs) that can be effectively used in simulations of combined heat and power (CHP) systems. Reciprocating engines are among the most common types of power generation units in CHP systems. In the literature, constant engine efficiencies or empirical efficiency curves are commonly used in the simulations for CHP performance evaluation. These methods do not provide realistic results for the design and component selection processes. The main advantage of this model is that it provides estimates of performance/efficiency maps for both electrical power output and useful thermal output for various capacities of engines without experimental data. The intent of this model is to provide performance/efficiency maps during a preliminary CHP design/simulation process. An example of model calibration to a specific CHP application is presented to demonstrate the capability and benefit of this model. The simulation results are validated with manufacturer’s technical data.
Kinematic Analysis and Design of a Two Body Articulated Robotic Vehicle
Authors: Farmer Jesse L. , Reinholtz Charles
Published: July 2010

The kinematic analysis and design of an articulated twin body, four-wheel, robotic vehicle is presented. The mobility of the vehicle is improved by connecting the two bodies with a four-bar linkage rather than the standard revolute-jointed body connection used in earlier designs. When properly proportioned, the new linkage design passively minimizes vehicle off-tracking by allowing the rear wheels to closely track the path of the front wheels. This significantly improves the ability of the vehicle to deal with cluttered environments. We outline the theoretical kinematic model of the four-bar linkage as applied to a twin-bodied, differentially driven vehicle. This model is validated through computer simulation as well as experimentation on a fully operational robotic vehicle. The kinematic model provides the foundation for an actively-controlled, linkage-based tracking system.
Flow Instabilities From a Parabolic Thermal Wall Profile in an Annular Cavity
Authors: Dillon Heather , Emery Ashley , Mescher Ann
Published: July 2010

During the drawing of optical fibers in an enclosed furnace the heat transfer to the fiber is due to both radiation from the furnace walls and free convection from the ambient gas. The stability of the free convection is a function of the furnace wall temperature distribution and of the iris temperatures. Experimental results are presented that show how the iris temperature affects the frequency of the convective flow oscillation in a simplified annular geometry. The flow possesses hysteresis in that as the iris temperature is increased and then decreased, the oscillatory flow does not return to its initial condition. All of the flow behavior studied in the annular geometry was three-dimensional.
Numerical Simulation of a Simulated Film Cooled Turbine Blade Leading Edge Including Conjugate Heat Transfer Effects
Authors: Dobrowolski Laurene D. , Bogard David G. , Piggush Justin , Kohli Atul
Published: July 2010

A conjugate numerical method was used to predict the normalized “metal” temperature of a simulated turbine blade leading edge. This computational study was done in conjunction with a parallel effort to experimentally determine normalized metal temperature, i.e. overall effectiveness, using a specially designed model blade leading edge. Also examined in this study were adiabatic models which provided adiabatic effectiveness results. Two different film cooling configurations were employed. The first configuration consisted of one row of holes centered on the stagnation line. The second configuration had two additional rows located at ±25 degrees from the stagnation line. These simulations were run at two different blowing ratios, M = 1 and M = 2. The coolant to mainstream density ratio was 1.5. The computational simulation was conducted using the FLUENT code using the realizable k-ε turbulence model and with grid resolution within the viscous sublayer. Adiabatic effectiveness distributions were predicted well by the computational simulations, except for localized areas near the holes. Predictions of overall effectiveness were higher than experimentally measured values in the stagnation region, but lower along downstream section of the leading edge. Reasons for the differences between computational predictions and experimental measurements were examined.
Numerical Modeling of Pressure Losses Caused by Bends in Pneumatic Conveying Pipeline
Authors: Cui Jie
Published: July 2010

Pneumatic conveying pipelines are widely employed in many industries to transport granular solids. Use of bends with various turning radii in these pipelines is mandatory and it is well known that the bends cause a loss of energy which results in an additional pressure drop. The pressure loss associated with various bends in pneumatic conveying pipelines was studied numerically. The numerical modeling results were validated against laboratory measurements, and parametric studies were performed to examine various factors that affect the pressure loss caused by bends in pneumatic conveying pipelines. Since the numerical results supply flow information at every location in the pipeline, the flow pattern and pressure field of air and pellet were resolved in detail to investigate the mechanism of the pressure loss in such systems.
Molecular Dynamics Study of Temperature Effects on Electrokinetic Transport in Si Nanochannel
Authors: Jelinek Bohumir , Felicelli Sergio D. , Mlakar Paul F. , Peters John F.
Published: July 2010

We studied temperature effects on the electrokinetic transport in the nanochannel with a slab geometry using a molecular dynamic (MD) model. A simple, previously published system consisting of Na+ and Cl− ions dissolved in water and confined between fixed crystalline silicon walls with negatively charged inner surfaces in an external electric field was chosen as a benchmark. Dependence of the fluid flow on the temperature and thermostating techniques was examined. The variation of resulting areal mass flux density and molecular velocity profiles across the channel with initial conditions was explored to asses the statistical significance of the results. It was found that, at least at the size scale, surface charge density, electric field and ionic concentrations of the benchmark system, the water flux and even its direction are directly controlled by temperature.
Large-Eddy Simulation of Turbulent Flow Through Small Gage Gas Appliance Orifices
Authors: Tanbour Emad Y. , Rahmani Ramin K. , Ayasoufi Anahita
Published: July 2010

Small orifices are widely used in different industries including gas appliances. Although characteristics of orifices such as their coefficient of discharge have been subject of interest for the past several decades, most of the previous studies focus on relatively high Reynolds number flow through relatively large diameter orifices. Moreover, the majority of previous work has focused on incompressible flows. This study focuses on the flow of different compressible gaseous fluids inside small orifices ranging from 1.3 mm to 2.1 mm hydraulic diameters for flow Re numbers of ∼8000 to ∼26000. Large-Eddy Simulation for turbulent flow is employed to solve the second-order discrete equations for compressible and incompressible flows in gas appliance orifices to predict the flow characteristics for relatively low-Re compressible flows in orifices widely used in gas appliance industry. The impacts of fluid material, the orifice hydraulic diameter, and the orifice profile on the characteristics of orifice are studied.