bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigations of Scale Effect on Cavitation Around Hydrofoils
Authors: Wang Haiyu , Shi Weidong , Zhang Desheng , Zhou Ling , Pan Dazhi
Published: December 2014

Although scale effects on cavitation have been studied, there seems to be no experimental or numerical work has been done on scale effects on cavitation regimes for hydrofoils. The present study was motivated by the prediction uncertainty of cavitation performance in scaling an axial flow pump, which is also an indispensable step in the design and application of hydraulic machineries. Hydrofoil NACA66 was adopted in this paper to represent the general characteristics of hydrofoils. Three hydrofoils with similar boundary conditions were simulated and analyzed, i.e. the initial hydrofoil, the hydrofoil models scaled down 0.5 and 0.25 times, respectively. High quality hexahedral mesh was established based on three-dimensional geometry of the hydrofoils. The monitoring points were arranged at the same locations relative to the boundary in each case. Computations were conducted on these three-dimensional hydrofoils, based on Detached Eddy Simulation (DES) turbulence model and Zwart cavitation model, which is a homogeneous model of cavitation, considering vapor/water mixture as one phase. In order to validate the practicability of numerical method and configuration employed in this paper, the numerical calculation of the initial hydrofoil was compared with experimental results provided by previous researchers, including the evolution of cavitation and pressure fluctuation on suction surface of the hydrofoil. According to the comparisons of the simulation results of the initial case and the other two scaled down models, we found the boundary layer suppresses the reentrant jet, which plays a critical role in cavitation detachment. Consequently, it influences the evolution of cavitation from the initial bubble, sheet cavitation, cloud cavitation and bubble breakup. Meantime, cavity evolution, cavity lengths, as well as cloud shedding periods were analyzed and discussed.
Heat Transfer Enhancement of Channel Flow via Vortex-Induced Vibration of Flexible Cylinder
Authors: Shi Junxiang , Hu Jingwen , Schafer Steven R. , Chen Chung-Lung (C. L. )
Published: December 2014

Thermal diffusion in a developed thermal boundary layer is considered as an obstacle for improving the forced convective heat transfer rate of a channel flow. In this work, a novel, self-agitating method that takes advantage of vortex-induced vibration (VIV) is introduced to disrupt the thermal boundary layer and thereby enhance the thermal performance. A flexible cylinder is placed at the centerline of a rectangular channel. The vortex shedding due to the cylinder gives rise to a periodic vibration of the cylinder. Consequently, the flow-structure-interaction (FSI) strengthens the disruption of the thermal boundary layer by vortex interaction with the walls, and improves the mixing process. This new concept for enhancing the convective heat transfer rate is demonstrated by a three-dimensional modeling study at different Reynolds numbers (84∼168). The fluid dynamics and thermal performance are analyzed in terms of vortex dynamics, temperature fields, local and average Nusselt numbers, and pressure loss. The channel with the self-agitated cylinder is verified to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% as opposed to the clean channel and the channel with a stationary cylinder, respectively.
Numerical Investigations of Drop Solidification by a Front-Tracking Method
Authors: Vu Truong V. , Tryggvason Gretar , Homma Shunji , Wells John C. , Takakura Hideyuki
Published: December 2014

We present a front-tracking/finite difference method for simulation of drop solidification, where the melt is confined by its own surface tension. The problem includes temporal evolution of three interfaces, i.e. solid–liquid, solid–air, and liquid–air, that are explicitly tracked under the assumption of axisymmetry. The solid–liquid interface is propagated with a normal velocity that is calculated from the normal temperature gradient across the front and the latent heat. The liquid–air front is advected by the velocity interpolated from nearest bulk fluid flow velocities. Method validation is carried out by comparing computational results with exact solutions for two-dimensional Stefan problems, and with related experiments. We then use the method to investigate a drop solidifying on a cold plate in which there exists volume expansion due to density difference between the solid and liquid phases. Effects of the tri-junction in terms of growth angles on the solidification process are also investigated. Computational results show that a decrease in the density ratio of solid to liquid or an increase in the growth angle results in an increase in the height of the solidified drop. In addition, reducing the gravitational effect also increases the drop height after solidification.
Experimental Investigation of Blade Rows Interactions in Contra-Rotating Axial Flow Pump
Authors: Cao Linlin , Honda Hironori , Yoshimura Hiroaki , Watanabe Satoshi , Furukawa Akinori
Published: December 2014

As a high specific speed pump, the contra-rotating axial flow pump with two rotors rotating reversely has been proved with higher hydraulic and cavitation performance, while in our previous researches, our prototype rotors designed with equal rotational speeds for both the front and the rear rotors was also confirmed with the strong potential interaction between two blade rows. In the present study, the experimental investigations were focused on the rotor-rotor interactions in the contra-rotating rotors under two rotational speed combinations, an equal speed and a different speed ones with the lower speed of rear rotor; the latter is determined aiming at relieved rotor-rotor interaction. As the major experimental approach, casing wall static pressure measurements were conducted at pressure taps covering from upstream to downstream of the both rotors, and the pressure fluctuation modes were investigated by the FFT analyses. By series of pressure taps with different peripheral locations prepared at several axial locations, the pressure fluctuation modes with frequencies non-synchronous to the BPF (blade passing frequency) components were recognized, and confirmed to be related to the rotor-rotor interaction on the basis of theoretical analyses on the rotor-stator interaction in conventional rotor-stator types.
Experimental Measurements in Near-Wall Regions by Particle Image Velocimetry (PIV)
Authors: Li Puxuan , Eckels Steve J. , Mann Garrett W. , Zhang Ning
Published: December 2014

The current study investigates the flow field near a surface with a micro-PIV system using a square tube to enhance optical access. Measurements of velocity fields and eddy structures near the wall of tubes are important to the design of in-tube surface geometries. In experimental fluid mechanics, particle image velocimetry (PIV) is now a common way to measure velocity. However, PIV measurements near walls require efforts to deal with low particle density, high shear gradient and wall reflection. The current paper discusses a PIV measurement technique utilized to observe flow dynamics in near-wall regions. PIV uncertainty analysis is discussed in this study. The experimental results are compared with previous results for validation.
Characteristics of Coherent Structures in Channel Flows During Low Reynolds Number Mixed Convection
Authors: Elatar Ahmed , Siddiqui Kamran
Published: December 2014

Characteristics of coherent structures generated in channel flows during low Reynolds numbers mixed convection have been investigated in a square channel. The Gr/Re2 ranged between 21 and 206 which indicates that natural convection was dominant over forced convection. Two-dimensional velocity fields were measured using particle image velocimetry (PIV) technique in different planes to obtain a three-dimensional perspective of the flow field in the channel. The coherent structures were detected from the turbulent velocity fields using an algorithm based on the velocity gradient tensor second invariant (Q). The location of each detected coherent structure was recorded and its turbulent kinetic energy was computed. It was found that the strength of coherent structures increased with an increase in the bottom wall temperature. The results also indicate that the coherent structures present in the region away from the bottom heated wall were more energetic compared to the coherent structures present within the thermal boundary layer.
Flashing of Pressurized Slurry in Metallurgical Processing: A Review of the State of the Art, Operational Experiences, and Recommendations for Future Research
Authors: Blackmore Adam , Shah Umesh , Pearson Murray , Plikas Atanasis , Sim Bonnie
Published: December 2014

Flashing of high temperature, pressurized slurry within hydrometallurgical processing circuits is a commonly encountered multiphase flow scenario, which can lead to catastrophic equipment failure and serious operational problems if not designed correctly. The current work aims to shed light on the state of the art modelling and experimentation, important physical phenomena, and recent operational experience surrounding this problem. In addition, recommendations will be provided for future modelling and experimental efforts in order to direct research into avenues that provide valuable information for engineers designing piping and vessels where the flashing of high pressure slurry occurs.
Towards the Enhancement of the Crystallization Kinetics of a Bio-Sourced and Biodegradable Polymer PLA (Poly (Lactic Acid))
Authors: Refaa Zakariaa , Boutaous Mhamed , Xin Shihe , Bourgin Patrick
Published: December 2014

PLA (Poly Lactic Acid) is a bio-sourced and a biodegradable polymer. It represents an interesting substitute for some petrochemical based polymers, especially because of its wide range of applications in the biomedical, agriculture and packaging fields. Unfortunately, PLA exhibits slow crystallization kinetics, limiting the amount of crystallinity in the final product, which is a handicap in order to extend its use. Many authors have investigated the crystallization of polymers; nevertheless several physical mechanisms remain not yet understood.

This work aims a complete characterization of PLA in order to improve the understanding of its crystallization kinetics. The quiescent crystallization was investigated using Differential Scanning Calorimetry (DSC) measurements in isothermal and non-isothermal conditions for PLA and PLA with 5wt % talc. The flow effect on crystallization was studied using a thermocontrolled hot-stage shearing device (Linkam) coupled with an optical microscope. The number of activated nuclei and the growth rate were measured as functions of temperature. In addition, the linear viscoelastic properties were obtained from a rheometer with plate-plate geometry.

The enhancement of the crystallization was quantified and analyzed in terms of the half crystallization time t1/2.

This characteristic time t1/2 is found to be drastically decreased by both the talc and the flow which promote supplementary nucleation leading to various crystalline microstructures. The flow is known to orient and stretch molecules leading to an extra nucleation. An original description of this phenomenon is proposed using two characteristic Weissenberg numbers; based on the definition of Rousse and reptation times.

Finally, we have proposed a semi-empirical model to quantify the thermal and flow contributions on the crystallization.
Numerical Simulation of Rotor-Tower Wake Interaction in Wind Farm
Authors: Gao Xiangyu , Zhou Nina , Chen Jun
Published: December 2014

This paper presents a numerical simulation of unsteady flow over wind turbine arrays to understand rotor-rotor and rotor-tower wake interaction in wind farms. The computations are carried out by incorporating Actuator Line method into a large eddy simulation. This methodology is validated by comparing the results to predictions of large eddy simulation using exact 3D blade geometries from a two-blade NREL Phase VI turbine. The method is then used to simulate the wake development in a two-turbine case. It is discovered that in the full wake setting the tower has a significant influence on the central part of the turbine wake. It is observed that the tower wake is twisted due to the rotation of the turbine wake. As a result, this tower wake is expected to have impact on the performance of downstream wind turbines, which cannot be overlooked. The present work also demonstrates the potential of combining AL method with LES to predict wake interactions in wind farms.
Reacting Turbulent Flow Simulation to Improve the Mixing Process in an Oil Refinery Incinerator
Authors: Darbandi Masoud , Abrar Bagher , Barezban Mohammad B. , Faridvand Amin , Schneider Gerry E.
Published: December 2014

Combustion emission is one of the most important issues in the design of industries. Todays’ strict environmental standards have limited the productions of CO, NOx, SOx, and other hazardous pollutants from the related industries. In this work, we study a typical oil refinery incinerator, which is used to burn waste gases residue produced during bitumen production process. The waste gas mainly includes a mixture including N2, H2O-vapor, and O2 species. Additionally, there are significant amounts of CO species and CxHy droplets in the waste gas composition. The measurements show that the CO emission becomes so crucial in high flow rate of feeding waste gas to the incinerator. Here, we numerically simulate the combustion process in this incinerator by solving the full turbulent reacting flow equations. In this regard, we use the finite-volume method to solve the RANS equations. For turbulence modeling purposes, we use the two-equation k-ε model along with standard wall functions. The non-premixed combustion is simulated by solving the mixture fraction equations for both fuel and waste gas streams. The interaction between turbulence and combustion is properly considered in the current modeling. We use the P1 method to solve the radiation transfer equation in emitting and absorbing medium of combustion gasses. The WSGG model is used to consider the absorption coefficient variation. The set of governing equations are solved using a SIMPLE-based algorithm. The current solutions provide good knowledge about the mixing pattern of flue gas and air-fuel streams in the incinerator. The improper mixing in the incinerator suggests we present a new design to re-design the waste gas inlet to the incinerator. Our simulation shows that the new design would result in substantial improvement in mixing process of these two streams. We find that this new design would effectively reduce the CO ppm at the exit of incinerator’s stack.
Effect of a SDBD on the Drag of a Half-Submerged Cylinder in Crossflow
Authors: Futrzynski Romain , Efraimsson Gunilla
Published: December 2014

In this paper the effect of a SDBD-type plasma actuator on the flow over a half-submerged cylinder is investigated numerically. The actuator is modeled via a body force, which is steady in time and where an exponential decay in space is assumed. First, the parameters in the numerical actuator model are determined for the case of no flow by optimization relative to experimental data. Thereafter, numerical solutions for the case with flow are studied numerically with and without actuation. A grid study is performed to check that the flow structures are resolved in both space and time. The effect of the actuator is examined. Although no significant change is observed when using the optimized parameters, using a stronger body force yields a reduction in drag of the order of 5%.
An Optimal Design Approach for the Decay Heat Removal System in PGSFR
Authors: Kim Dehee , Eoh Jaehyuk , Lee Tae-Ho
Published: December 2014

Sodium-cooled Fast Reactor (SFR) is one of the generation IV (Gen-IV) nuclear reactors. Prototype Gen-IV SFR (PGSFR) is a SFR being developed in Korea Atomic Energy Research Institute (KAERI). Decay Heat Removal System (DHRS) in the PGSFR has a safety function to make shutdown the reactor under abnormal plant conditions. Single DHRS loop consists of sodium-to-sodium decay heat exchanger (DHX), helical-tube sodium-to-air heat exchanger (AHX) or finned-tube sodium-to-air heat exchanger (FHX), loop piping, and expansion vessel. The DHXs are located in the cold pool and the AHXs and FHXs are installed in the upper region of the reactor building. The DHRS loop is a closed loop and liquid sodium coolant circulates inside the loop by natural circulation head for passive system and by forced circulation head for active system.

There are three independent heat transport paths in the DHRS, i.e., the DHX shell-side sodium flow path, the DHRS sodium loop path through the piping, the AHX shell-side air flow path. To design the components of the DHRS and to determine its configuration, key design parameters such as mass flow rates in each path, inlet/outlet temperatures of primary and secondary flow sides of each heat exchanger should be determined reflecting on the coupled heat transfer mechanism over the heat transfer paths. The number of design parameters is larger than that of the governing equations and optimization approach is required for compact design of the DHRS. Therefore, a genetic algorithm has been implemented to decide the optimal design point. The one-dimensional system design code which can predict heat transfer rates and pressure losses through the heat exchangers and piping calculates the objective function and the genetic algorithm code searches a global optimal point.

In this paper, we present a design methodology of the DHRS, for which we have developed a system code coupling a one-dimensional system code with a genetic algorithm code. As a design result, the DHRS layouts and the sizing of the heat exchangers have been shown.
CFD Modelling of Bubbly Flow in Adiabatic Upward Pipe Using a Solver Based on OpenFOAM® With the Quadrature Method of Moments
Authors: Peña-Monferrer Carlos , Passalacqua Alberto , Chiva Sergio , Muñoz-Cobo José L.
Published: December 2014

An Eulerian-Eulerian approach was used to model adiabatic bubbly flow with CFD techniques. The OpenFOAM® solver twoPhaseEulerFoam was modified to predict upward bubbly flow in vertical pipes. Interfacial force and bubble induced turbulence models are studied and implemented. The population balance equation included in the two-fluid model is solved to simulate a polydisperse flow with the quadrature method of moments approximation. Two-phase flow experiments with different superficial velocities of gas and water at different temperatures are used to validate the solver. Radial distributions of void fraction, air and water velocities, Sauter mean diameter and turbulence intensity are compared with the computational results. The computational results agree well with the experiments showing the capability of the solver to predict two-phase flow characteristics.
A Numerical Analysis of the Turbophoresis in a Turbulent Gas-Particle Flow
Authors: Utzig Jonathan , de Souza Francisco José , Meier Henry França
Published: December 2014

Gas-particle flows are very commonly found in pharmaceutical, chemical and petroleum industries. The optimization of the operations involved normally requires a detailed knowledge of the very intrinsic phenomena that take place within the equipment handling the mixture. Once multiphase flows have peculiar characteristics, their behavior should be extensively evaluated. One of these characteristics is the turbophoresis, which occurs in turbulent confined gas-solid flows. The dispersed phase concentrates at the walls and forms a segregated particle flow, where high mass-loading effects become important. Thus, in this work the Euler/Lagrange approach to three-dimensional unstructured meshes is used to numerically assess the turbophoretic effect. The influence of the coupling between phases (two- and four-way coupling) and wall roughness are taken into account. Results show that the particle deposition depends on the coupling and wall roughness. Four-way coupling effects are observed to increase the turbophoresis phenomenon and modify the gas phase dynamics.
Numerical Analysis of Compressible Fluid Flow in Narrow Gaps
Authors: Kefalas Alexander , Benra Friedrich-Karl , Dohmen Hans Josef
Published: December 2014

Fluid flow in a narrow gap is a characteristic problem in fluid mechanics. In today’s turbomachines several applications are based on the phenomena of two surfaces being separated by a thin fluid film of only a few micrometers. In this contribution a numerical model is introduced to determine flow characteristics of compressible fluids, contained between two concentric non contacting rotating rings. The model is based on the assumption of a laminar viscous flow field and isothermal conditions. Furthermore it takes aerostatic and aerodynamic effect into account. A finite difference approach to solve the models governing equation is described and methods to improve convergence are introduced. To perform the established numerical model on a wide variety of geometric configurations an interface between a 3D-CAD design software and the numerical model has been developed and is presented in this paper.
Prediction of Aerodynamic Loadings and Power Productions of Wind Turbines in Wake by Numerical Simulation
Authors: Zhou Nina , Gao Xiangyu , Chen Jun
Published: December 2014

In this paper, the Large Eddy Simulation coupled with the Actuator line (LES-AL) method is employed to analyze the performance of the downstream wind turbine under varying inflow conditions. A direct LES, which solves the flow physics around turbine blades using exact three-dimensional blade geometries, is carried out to predict the aerodynamic loadings and output powers of the downstream turbines by prescribing the wake profiles predicted by LES-AL simulation as the inflow boundary conditions. The upstream tower shadow effect is presented in this study by carrying out two simulations with no tower wake and real tower wake inflow conditions. The LES results show that both the power and aerodynamic loading components fluctuate periodically due to the presence of upstream tower. In additional, an additional force component is exerted on the downstream wind turbine in the vertical direction (z direction). The increase in velocity deficit in wake in behind the downstream turbine is due to a sequence of momentum extraction by the wind turbines. The tower shadow effect accumulates and generates lower velocity regions in wake, and the low velocity regions shift due to the rotational motion of wake vortex. The development of the asymmetric and velocity deficit region has the potential to generate more unstable power output and fatigue loading on turbines in further downstream.
On the Response of Planar Wakes to Asymmetric Initial Conditions
Authors: Momayez Ladan , Dghim Marouen , Ferchichi Mohsen , Graveline Sylvain
Published: December 2014

This work reports an experimental investigation on the response of a planar wake generated by a profiled flat plate to various upstream flow conditions. A tripping wire was placed on the upper side of the flat plate just downstream of the leading edge of the plate that resulted in asymmetric separating shear layers at the trailing edge. The near wake asymmetry is compared to the symmetrical case at two different Reynolds numbers. Two asymmetric initial conditions resulted, namely, laminar boundary layer on the lower side and a turbulent boundary layer on the upper side, and a turbulent boundary layer on the lower side and tripped turbulent boundary layer on the upper surface. The near wake dynamics were investigated under the effects of the degree of asymmetry using hot-wire anemometry and flow visualizations. The measurements showed when one of the two boundary layers was tripped, the wake shifted towards the tripped side and wake spreading was found to be larger than in the case of the symmetrical wake with the effect being more pronounced in the asymmetric laminar wake. Self-similarity of the asymmetrical wakes was established by properly selecting appropriate similarity variables however, the similarity of the wake was less evident in the tripped laminar boundary layer case. Convection velocity, Uc, of the Von Karman large eddies, estimated using processed flow visualization images seemed to increase with increased Reynolds number and with increased upstream momentum thickness. In the symmetric laminar wake, Uc/U∞ increases from 0.2 and reached an asymptotic value of about 0.85 further downstream. In the presence of perturbation, Uc/U∞ attained a constant value of about 0.83 further downstream compared to the symmetric case. For the turbulent wake, however, asymmetry of the turbulence levels was found to increase the convection speed compared to both the laminar wake and the symmetric turbulent wake reaching a constant value nearly at the same downstream position for both the symmetric and asymmetric turbulent wake.
Multiscale Approach for Particulate Flows, Application to Fluidized Beds
Authors: Bernard Manuel , Wachs Anthony , Climent Eric
Published: December 2014

In this paper, a discrete element method (DEM) coupled with computational fluid dynamics (CFD) and a distributed Lagrange multiplier - fictitious domain method (DLM-FD) are used is order to model three-dimensional fluidized beds. Particle-particle and wall-particle contacts are handled thanks to a soft sphere model. For the DEM-CFD model, also called Euler-Lagrange model, fluid dynamics variables are locally averaged and solved on a grid larger than the particle size whereas for the DLM-FD grid cells are around 20 times smaller than the particle characteristic length. The aim of this work is to extract information from DLM-FD simulations to improve the correlations used in the DEM-CFD model. First, particles and fluid equations are presented for the Euler-Lagrange model. Then, fluid-particle interaction is detailed. Eventually, we present preliminary simulations and results with both models in a 3D fluidized bed configuration.
Dimensionality of Anisotropic Homogeneous Turbulence With Distortions: Compared Effects Between the Coriolis Force and the Lorentz Force
Authors: Godeferd Fabien , Cambon Claude , Delache Alexandre
Published: December 2014

We consider initially isotropic homogeneous turbulence which is submitted to an external force, in statistically axisymmetric configurations. First, we study hydrodynamical turbulence in a rotating frame, in which case the Coriolis force modifies the structure and dynamics of the flow, thus creating elongated structures along the axis of rotation, corresponding to an accumulation of energy in the neighbourhood of the equatorial spectral plane. Secondly, a very similar configuration is that of magnetohydrodynamics (MHD) of a conducting fluid within an externally applied space uniform magnetic field, in which case the Lorentz force also concentrates energy to the same spectral equatorial manifold, but creates axially extending current sheets, along the magnetic field. We more specifically consider the quasi-static limit at small magnetic Reynolds number, in which the induction equation is analytically solved. We study the anisotropy of each turbulent flow using progressively refined statistics applied to results of direct numerical simulations, and we show that an accurate characterization of the flow structure requires advanced two-point statistics, which are available easily only in spectral space.
Acoustic Streaming Jets in Liquids
Authors: Botton Valéry , Moudjed Brahim , Henry Daniel , Ben Hadid Hamda , Garandet Jean-Paul , Potherat Alban
Published: December 2014

Theoretical and experimental investigations of acoustic streaming jets in water are described. The jet is produced by a plane circular ultrasonic transducer in a cavity inside a water tank, either in the near field or in the far field of the acoustic beam. The approach combines an experimental characterization of both the acoustic field and the obtained acoustic streaming velocity field on one hand, with both scaling analysis and CFD using an incompressible Navier-Stokes solver on the other hand. It is shown that good comparisons between experimental and numerical results can be obtained with a theoretical model based on a linear acoustic propagation model accounting for diffraction coupled to a hydrodynamic model including inertia effects. The coupling is obtained by the introduction of a momentum source term, the acoustic streaming force, in the hydrodynamic model. Both experimentally and numerically, the shape of the flow is thus found to be directly affected by both the overall shape of the acoustic beam and the local variations in acoustic pressure amplitude, in particular in the acoustic near field. Through scaling analysis, two scaling laws featuring linear or square root variations of the streaming velocity level with the acoustic power have been found. These scaling laws are shown to apply with a reasonable agreement to our numerical and experimental data, as well as to other former experimental investigations found in the literature.
Physical Model Study of the Wind Turbine Array Boundary Layer
Authors: Charmanski Kyle , Turner John , Wosnik Martin
Published: December 2014

First results from an experimental investigation of the fully developed wind turbine array boundary layer are reported, using arrays of up to 100 model wind turbines with a diameter of 0.25 m. The wind turbine array was simulated by a combination of drag-matched porous disks, used in the upstream part of the array, and by a smaller array of realistically scaled 3-bladed wind turbines just upstream of the measurement location. The model array was placed in the 6.0 m × 2.7 m × 72.0 m test section of the UNH Flow Physics Facility. Power, rate of rotation and rotor thrust were measured for select turbines, and hot-wire anemometry was used for flow measurements. Development of a fully developed wind turbine array boundary layer was noted with increase in array size.
Fluidic Deformation Under Hypervelocity Impacts
Authors: Thurber Andrew , Bayandor Javid
Published: December 2014

The increased frequency of exploration into space has caused a dramatic rise in the density of debris in orbit. Orbital debris, both natural and man-made, poses an extreme impact risk to satellites and spacecraft. The relative velocities between orbital components and debris can exceed thousands of meters per second, giving rise to immense kinetic energies even for small objects. In such a hypervelocity impact event, the shock pressures exceed the strength of common aerospace materials, and brief shock-induced temperature rises cause melting and vaporization of most structural bodies. Under these extreme conditions, the failure and deformation of solids can resemble fluid flow. By using meshless Lagrangian models in an explicit computational framework, this work identifies analogous fluidic interactions and further quantifies the role of shear and inertial forces in hypervelocity impacts (HVI).
Investigation of Exhaust Conditions on Influencing Contaminant Transport for Indoor Environments
Authors: Zheng Z. C. , Wei Z. , Bennett J. S.
Published: December 2014

Indoor air quality is an important issue involved in a wide variety of industrial applications. In an indoor environment, different types of contaminants exist and have an inevitable potential to cause health problems for human beings and animals. In this study, the focus is on the contaminant contained in painting materials. While painting materials being sprayed to solid surfaces, pollutant plumes are formed near the painting area, which may enclose the body parts of the sprayers. Severe health problems are possible to occur if a significant amount of painting materials settles on the face of workers. By applying exhaust conditions (i.e. exhaust fan with outlet velocity), the flow convection in the room can be enhanced, which may alleviate the contaminant level on the human body. In such a case, the choice of exhaust condition becomes crucial. With the aid of computational fluid dynamics, an optimal exhaust condition can be determined. To simulate this kind of fluid/solid-particle multiphase flow, the current study employs a pure Eulerian or Euler-Euler type model. In the Euler-Euler approach, the properties of the contaminant particles are assumed to be continuous as those of fluids and all phases are computed in the Eulerian framework. Since the exhaust speed is moderately low and fully turbulent flow is not guaranteed in the room, the RNG k-e model is used as a low Reynolds number turbulent model. The current paper firstly investigated the scenario of sprayer self-contamination. Then, inter-contaminations among different workers will be studied.
Unsteady Flow Analysis Strategies for Flapping Flight
Authors: Asbury Paul , Nichols Rachel , Gadell Greg , Elsheikh Mohamed , Galbraith Brandon , Horton Brandon , Marino Josh , Nesaw Chris , Kossa Michael , Collie Zachary , Amaya Joseph , Feaster Jeffrey , Bender Matthew , Matta Alexander , Bayandor Javid , Kurdila Andrew , Battaglia Francine , Mueller Rolf
Published: December 2014

A current project is underway to create a prototype of an anatomically correct seagull with biologically accurate flight kinematics. The presented work is focused on the computational fluid dynamics (CFD) analysis of bird flight kinematics. A finite volume approach, using Fluent, was used to attempt to model the kinematics of bird flight with varying degrees of freedom to analyze the lift, drag, pressure, and vortices magnitude associated with a range of flight kinematics. Dimensional analysis has been performed to analyze the effects of angle of incidence on the different sections of a seagull wing. Validated CFD analysis has been performed to identify optimal degree of freedom for generating maximum amount of lift while minimizing drag.

The analysis benefitted from dynamic meshing and a user defined function to model the seagull wing, profiles of which were approximated by the S1223 airfoil. The user defined function allowed for variation of degrees of freedom to model the flight in the current bird prototype and to assess the effects of changing angles of incidence and inlet velocity on lift and drag. Difficulties were encountered when trying to accurately analyze unsteady aerodynamics over a flapping motion. The appropriate grid resolution, the user defined function, as well as the appropriate grid and dynamic mesh parameters within Fluent were all possible areas of concern. The grid resolution was determined by analyzing a steady state case and determining the variation in lift and drag values calculated by increasing the grid density. A user defined function was created that accurately represents the kinematics associated with the bird wing. A triangular grid was utilized for the dynamic mesh with re-meshing procedure activated at every iteration during the analysis. The final geometry provided an accurate method for dynamic re-meshing and overcame the problem of negative cell volume associated with re-meshing using a rectangular mesh configuration. It was determined that maximum cell volume, number of time steps, and time step interval were all important criteria when determining parameters for the unsteady flight analysis.

Results indicate that the unsteady dynamics of bird flapping motion can be effectively represented with modified CFD analysis with updated finite volume scheme. Data indicates that values associated with varying angles of attack at a steady state cannot be used to model flapping flight. The paper will report on further validation to analyze the pressure, lift and drag associated with flapping flight in a three-dimensional study.
Viscous Droplet Interaction With Micro-Textured Solid Surfaces
Authors: Beussman Kevin M. , Wang Yechun
Published: December 2014

The dynamics of viscous droplets near solid surfaces, especially micro-textured surfaces, and the interaction between them are of great importance in industrial applications, biochemical processes, and fundamental materials research on surface wettability. In this work, a three-dimensional spectral boundary element method has been employed to investigate the dynamics of a viscous droplet falling under gravity influence to micro-textured solid surfaces. The droplet size, in this study, is comparable to the size of the surface texture. The influences of the Bond number, relative size of the droplet with respect to the surface features, and the topological characteristics of the substrate on the droplet motion and deformation are investigated. The stress exerted on the substrate due to droplet motion is also explored.
A Methodology for the Kinematic and Unsteady Dynamics Analysis of Bat Flight
Authors: Feaster Jeffrey , Matta Alex , Battaglia Francine , Kurdila Andrew , Müller Rolf , Bayandor Javid
Published: December 2014

A methodology to capture and post-process bat flight 3-D Stereo Triangulation data to formulate an approximated rigid body kinematic model was investigated. Bat flight is unique in nature due to the bats inherent agility and many degrees of freedom when compared to other flying animals. This complexity makes capturing accurate aerodynamic data very difficult. Unlike insects, which utilize few degrees of freedom and a high flap frequency for sustained flight and maneuverability, the agility of bats comes in part from the many degrees of freedom present in the bat wing. In order to better understand the aerodynamics present in bat flight, bats Hipposideridae (Old World leaf-nosed bats) were examined. The trajectories of critical points along the bat wings were recorded using 3D stereo triangulation techniques to capture the complexities of the bat flight. Markers were placed at all the joint locations along the bat wing. The resulting trajectories were then translated into a periodic kinematic model for future computational use.
Quantitative Visualization of Two-Phase Flow in the Head of Plate-Fin Heat Exchanger
Authors: Tu Xincheng , Kim Sung-jun , Kim Hyoung-Bum
Published: December 2014

In this study, we experimentally investigated the distribution of liquid and gas flow in the head of plate-fin heat exchanger. The scale-downed model of proto-type heat exchanger was used and the air and water replaced the natural gas and liquefied natural gas. Two CCD cameras were synchronized with laser to capture the image of liquid-gas flow in the head. Advanced imaging techniques such as LIF, PIV method were used to measure the velocity field of liquid and gas flow simultaneously. The characteristics of momentum transfer process between liquid phase and gas phase are presented in the terms of ensemble averaged result. The effect of liquid mass fraction on the flow distribution was investigated. Then, we quantified the flow distribution of liquid and gas phase for different inlet nozzle configurations.
Application of the Electroosmotic Effect for Thrust Generation
Authors: Hansen Thomas E. , Tawfik Mena E. , Diez F. J.
Published: December 2014

The present work focuses on demonstrating the capabilities of electro-osmotic pumps, EOPs, to generate thrust. EOPs have high power to volume ratio and operate on ionic aqueous solutions making them a good candidate for use as thrusters in miniature watercraft such as micro underwater gliders. Millimeter-size nano-porous membrane will be used to achieve milli-Newton thrust. Electro-osmotic pumps are operated under high electric fields to achieve highest thrust possible. A byproduct of high electric fields in EOPs is the generation of gas which is addressed by using bipolar rectangular wave pumping. This resulted in over 55% increase in flow rate when compared to DC pumping for the same average voltage while reducing gas generation. When properly sized and optimized for thrust, the feasibility of EOPs is demonstrated. This is the first experimental application of a membrane-based electro-osmotic pump for propulsion. Several membranes of different materials were tested including polymer and ceramic membranes. It was found that glass micro-capillary arrays are the most suitable membranes for electro-osmotic thrusters, or EOTs. Among their advantages include their rigid construction and ability to produce high flow rates.
Modeling the Operation Regimes in Ultra-High Temperature Continuous Reactors
Authors: Fedorov Sergey S. , Gubynskyi Mykhailo V. , Barsukov Igor V. , Livitan Mykola V. , Gogotsi Oleksiy G. , Rohatgi Upendra Singh
Published: December 2014

The main advantage of carbon material treatment in electro-thermal furnaces with fluidized bed [EFFB] at 2000–3000C is that they allow producing graphite of high chemical purity, which is especially important in manufacture of ion-lithium batteries. The team conducted extensive research into hydraulic and heat modes of such units and developed a methodology for their design based on the concept of increase in electric resistance with fluidization. The choice of the working space configuration and the operation mode of EFFB are largely determined by the specific electrical resistance [SER] of the fluidized bed. This parameter is a complex function of a number of factors: fluidization character, uniformity of the bed and the temperature, nature and size of the material fractions, current density and furnace atmosphere composition. It is vital to take into account relationships between SER, working temperature T and current density i, which eventually define electrothermal mode of the unit operation. Thus, if graphite size is d = 130μm within temperature range T = 0–2500C and current density i = 0,004–1.0 A/cm2, SER varies in reverse proportion to these parameters Statistic processing of the experimental data allowed to obtain regressive function SER = f (i, t), which we used as the basis of mathematic modeling, heat balance calculation and predicting transitory and operation modes of EFFB with 10kg/hour productivity: SER=0.01.84.711-2.,593*10-2.T-46.854*i+1.205*10-2.T*i,Ω-m′

Resulting volt-ampere characteristics (VACs) of the furnace have maximum values at constant temperature (T = const) which is explained by the non-linear character of the SER function. There exists a technological temperature limit of EFFB responsible for its stable operation. The furnace operation beyond the stability margin depends on the power source characteristics which may cause a sharp power drop or a shorting. The VAC characteristics are determined by the type of material, geometry of the furnace working space, electrode diameter, active zone height, the gap between the electrode and the lining, design of heat insulation and the cooling system. Taking these parameters into consideration, it is possible to conduct a preliminary analysis of the unit stable operation modes as early as during the design stage.
Numerical Study of the Free Convection Heat Transfer From an I-Beam Support Structure
Authors: Brimmo Ayoola T. , Shatilla Youssef , Hassan Mohamed I.
Published: December 2014

In this study, a computational fluid dynamics (CFD) model is used to numerically characterize the heat transfer from an I-beam support structure of an aluminum reduction pot, during the free convection cooling process. A slice of the I-beam structure is modeled on two different finite element commercial platforms, ANSYS (FLUENT) and StarCCM+, in a suitable domain of air. The K-epsilon Reynolds averaging technique is used to model the turbulence in both platforms. Validation of the modeling technique and parameters adapted is appropriately performed. The structure is segmented and space mean Nusselt numbers (Nu) characterizing the flow are calculated for each section, for Rayleigh number (Ra) ranges typically experienced by the respective section. Expressions correlating the free convection flow over this structure are deduced based on a regression analysis. To conclude, an application of the deduced correlation in modeling the free convection cooling of an aluminum reduction pot is presented.
Experimental Investigation on the Performance of Scroll Refrigeration Compressor With Suction Injection Cooling
Authors: Sun Shuaihui , Guo Pengcheng , Feng Jianjun , Zheng Xiaobo , Wang Zhizhong
Published: December 2014

Suction injection cooling can be usually used in scroll refrigeration compressor which works under the high speed or high pressure ratio condition, when the atmosphere is severe. In the present paper, the suction injection process is simulated with isobaric adiabatic mixing model, which has been employed by many researchers; and the performance of the scroll compressor with suction injection cooling was investigated experimentally. The test rig was established, and the scroll compressor with suction injection cooling was measured when the pressure ratio rose from 3.4 to 4.5, and the injection volume flow rate rose from 0 to 0.085 m3·h−1. The results indicate that the discharge temperature decreases remarkably with the injection volume flow rate. Also, the COP (Coefficient of Performance) decrease with the injection volume flow rate. When the injection mass ratio is lower than 20%, the decrease of COP is acceptable, at different pressure ratio. At high pressure ratio, the COP could keep unchanged when the injection mass ratio is lower than 10%. Hence, the effect of suction injection cooling is better at the high pressure ratio and low injection volume flow rate. The ideal simulation results agree well with the experimental ones at low injection volume flow rate, but deviate from that at high injection volume flow rate. This is because that the gas-liquid separation happened at high injection ratio, and the isobaric adiabatic mixing model could not predict the process practically. Therefore, a new model will be developed to describe the process accurately.