bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of Flow Separation and Its Associated Physics on a NACA0015 Using Synthetic Jet Actuators
Authors: Siauw Wei Long , Tensi Jean , Bourgois Se´bastien , Bonnet Jean-Paul , Breux Jean-Marc , Maria Ignacio
Published: September 2008

Wind tunnel flow control experiments are conducted on two NACA0015 airfoil models, one of which having a chord length of 1.0m and the other having a chord of 0.35m, with the aim of exploring the separated flow physics and delaying flow separation. The larger model is tested in a low speed wind tunnel, measuring 1.25m by 1.25m at a Reynolds number of 0.4 and 0.27 million. This model is used to provide a quick proof of concept concerning the efficiency of various synthetic jet designs. Laser light visualization and Particle Image Velocimetry (PIV) studies are performed on this model. The synthetic jet actuators implemented (mechanically and acoustically generated) is realized through holes (2 and 3mm in diameter). The actuators are positioned at 20% or 70% of chord length from the leading edge for controlling separation at incidences between 12° and 15°. Flow separation delay and reattachment, depending on the frequency and momentum of the synthetic jet are observed qualitatively via laser sheet visualization in all cases. The efficiency of the actuator is quantified via the extent of separation observed with the PIV measurements. The technique of Proper Orthogonal Decomposition (POD) is applied to further reveal the large eddies in the separated shear layer and its interaction with the boundary layer. The smaller model is tested in a larger wind tunnel measuring 2.4m by 2.6m at a Reynolds number of 0.9 million. This is a more realistic flow condition with minimal wall and aspect ratio influence as compared to the larger model. The main experimental objective concerning this model is to quantify the baseline aerodynamic of the NACA0015 before implementation of synthetic jets. Laser light and surface oil visualizations are performed. Measurements concerning surface pressure and wake velocity characteristics are also made for this model. The lift of which is estimated via the integration of surface static pressure and the drag is estimated by wake survey technique using a pitot tube that is made to traverse in the wake. In addition, time resolved data are obtained in the wake of the airfoil by means of hotwires. Both hotwire measurement reveal typical Strouhal number of 0.34–0.4. These results are extrapolated to the large airfoil for interpretation of the flow physics during control. To sum up, the main results in the current study highlight the characteristics of the baseline airfoil and the ability of synthetic jet actuator techniques to obtain significant delay of the separation.
A Study on Secondary Drops Produced by Droplet Collision With a Liquid Film
Authors: Okawa Tomio , Mori Toshiaki , Shiraishi Takuya , Kataoka Isao
Published: September 2008

The collision of single water drops with a plane water surface was investigated experimentally to elucidate the effect of impact angle on the amount of secondary drops. When the impact angle was not too small, the measured critical impact Weber number for the formation of secondary drops agreed with the experimental data reported in literature, provided that the absolute velocity of primary droplet was used in calculating the Weber number. The ratio of total mass of secondary drops to the mass of primary droplet increased markedly with the decrease of impact angle. Whereas, when the impact angle was too small, no secondary drops were produced within the experimental ranges tested.
Numerical Simulation of Hydro-Acoustic Flow of Liquid in Piezo Inkjet Print Head
Authors: Lee You-Seop , Chung Jae Woo
Published: September 2008

This paper presents numerical and theoretical studies of acoustic wave interactions in slightly compressible liquids within piezoelectrically driven inkjet print heads. The interconnected flow channels may cause jet cross-talk, resulting in poor printing quality. Thus, it should be reduced by modifying the channel structure with the acoustic wave interactions considered. Compressible gas flow driven by the sudden movement of a top wall in the channel is calculated using Flow3D and is validated with the result obtained by using the narrow gap theory. For the calculation of pressure waves in the ink flow, a limited compressibility model of the Flow3D is used. It is found that reducing the restrictor width can damp out the jet cross-talk by inhibiting the pressure wave propagation. The degree of cross-talk has been quantified using the maximum values of cross-correlations between neighboring channels and a critical channel dimension for acceptable cross-talk has been proposed. This finding is verified by drop visualization experiments using silicon-micromachined piezo inkjet print heads that are fabricated by our group.
Port DOE With Parametric Modeling and CFD
Authors: Korivi Vamshi M. , Cho Su K. , Amer Amer A.
Published: September 2008

Port design is an integral part of a combustion system. For a spark-ignited engine, it impacts both in-cylinder charge motion and performance potential. While turbulence intensity and air-mixture quality affect dilution tolerance and fuel economy as a result, breathing ability affects wide open throttle performance. Traditional approaches deploy experimental techniques to reach a target balance between the charge motion and breathing capacity. Such techniques do not necessarily result in an optimized solution. Unrelenting development of Computational Fluid Dynamics (CFD) tools, Design of Experiment (DOE) and optimization techniques combined with increased computational power led to the development of new methodologies over the past decade. Such advancements have the potential to deliver optimized solutions. Recent releases of engineering CAD packages, like CATIA V5 and Pro-Engineer, enable both parametric modeling and associative design update. This paper demonstrates a coupling process between CFD analysis and engineering CAD software using process integration and design optimization software (PIDO). CATIA V5, ICEM-CFD meshing tool and FLUENT-UNS CFD code were integrated to run through many port designs using ISIGHT. The automatic coupling was aimed at optimizing the port layout for a certain cost function such as flow restriction or charge motion, subject to manufacturing and packaging constraints. Accomplishing this task necessitates running the executables of various software using macros and scripts. This integrating methodology utilized best design practices for an intake port, and numerous numerical experiments were attempted. This methodology was demonstrated on a V-engine intake port with geometric, manufacturing and packaging constraints. In order to prove the methodology described, two distinct designs were attempted, the first of which demonstrated high flow at the expense of charge motion, while the other targeted tumble charge motion to the detriment of flow. Both concepts were prototyped and evaluated on the flow bench. Good correlation between simulation and test results was demonstrated in this study. It was concluded that this process could be reliably adopted in a production environment with reasonable amount of turn around time.
Bubble Interactions With Free Interfaces
Authors: Brady Michael R. , Telionis Demetri P. , Vlachos Pavlos P.
Published: September 2008

Bubble collisions with other bubbles, particles or interfaces are very important in a variety of mass transfer applications. The rise of a buoyant bubble and its interaction with a free liquid surface was experimentally investigated using a Time-Resolved DPIV system. The results are presented as functions of bubble size, and surfactant concentration of the fluid medium. It is shown that the presence of a surfactant significantly affects the approach and collision characteristics of the bubble. The addition of a surfactant changes the viscous forces around the bubble due to the adsorption coverage of the surfactant at the bubble-fluid interface. A bubble traveling through a surfactant solution (1e-3 M Sodium Dodecyl Sulfate) did not exhibit bouncing behavior regardless of its size. The flow is characterized by a vortex ring trailing the bubble during the approach stage. After impact, the vortex ring slowly diffuses away parallel to the wall and dissipates. In contrast a smaller (1.1 mm) bubble in pure water rebounded from the free surface three distinct times. The rebounding exhibits complex vortex interactions, and the vortices tend to dissipate more quickly than in the no-rebound case. Vortex dynamics play an important role in determining the energy dissipation. Comparisons with other computational and experimental works are combined with the present study to more accurately describe the dynamics of the bubble rebound.
Turbulence Characteristics in a Rushton Stirring Vessel Measured via Time Resolved DPIV
Authors: Brady Michael R. , Telionis Demetri P. , Vlachos Pavlos P.
Published: September 2008

Stirred vessels are devices that find extensive industrial applications particularly in mineral and chemical industries. Interactions of solid particles and/or bubbles and particles depend on the characteristics of turbulent flow. In many analytical models, the rate of collision is a function of turbulence dissipation. It has been known that dissipation levels are much higher in the neighborhood of the agitating mechanism, in our case the Rushton impeller. In this paper we use time-resolved DPIV to measure the velocity field with a spatial resolution down to 100 μm, and a frequency resolution of 500 Hz. The range of Reynolds numbers investigated varied from 20,000 to 50,000, with the smallest Kolmogorov length scale of about 15 μm. The flow in the impeller stream of a Rushton impeller can be best summarized as a radial jet with a pair of convecting tip vortices. The turbulence quantities were found by removing the periodic component from the blade passing, which is the dominant part of the measured velocities. Dissipation was calculated from the velocity gradients, and assuming isotropy. We provide further evidence that larger dissipation values in the vicinity of the impeller are consistent with the dynamic motion generated by the blade passage. This is somewhat anti-intuitive, because energy is dissipated at the smallest eddy scales, and the immediate vicinity of the impeller contains large vortical structures and provides little space or time for such structures to break down. The maximum and mean normalized dissipation in the impeller stream showed decreasing trends with the Reynolds number. Other normalized turbulence quantities, namely Vrms and in plane vorticity are presented. Our experiments agree very well with other experimental studies. Estimates of turbulence characteristics and in particular distributions of turbulent energy dissipation determined in this study will be used in estimating rates of collisions of bubbles and particles in stirred vessels.
Measurement of the Flow in a 170 MW Hydraulic Turbine Recording the Pressure-Time Rise in One Section of the Penstock
Authors: Sierra F. , Kubiak J. , Urquiza G. , Adamkoski A. , Janicki W. , Ferna´ndez J. M. , Basurto M.
Published: September 2008

The objective of the present work is to evaluate the performance of a hydraulic turbine by means of the measurement of flow using the Gibson method based on recording pressure–time rise in one section of the penstock and relate it to the pressure in the upper reservoir to which the penstock is connected. Volumetric flow is determined by integration of the time function of a differential pressure (between the section and the inlet to the penstock). Flow measurement was possible this way because the influence of penstock inlet was negligible as far as an error of the measurement is concerned. The paper presents the results obtained with this method for the case of a 170 MW hydraulic turbine. The length of the penstock was 300 m. Previous experience and a standard IEC-41-1991 were the criteria adopted and applied. An efficient and fast acquisition system including a 16 bit card was used. The flow rate was calculated using a computer program developed and tested on several cases. The results obtained with the Gibson method were used for calibration of the on-line flow measuring system based on the Winter-Kennedy principles. This last method is used for continuous monitoring of the turbine flow rate. Having calculated the flow rate and output power the efficiency is calculated for any operating conditions. A curve showing the best operating conditions based on the highest efficiency is presented and discussed. Flow simulation allowed having an estimation of a flow recirculation region size.
Length Scale Propagation Along a Joint Inlet and Thermal Buoyancy Driven Flow
Authors: Marr D. R. , Glauser M. N.
Published: September 2008

The objective of this research is the determination of length scale propagation in the average indoor cubicle environment associated with displacement ventilation. The presentation involves an extended analysis on experimental data taken in a cubicle sized room involving both a simplified ventilation technique and thermal occupant. A room of dimensions six by eight foot, similar to an office cubicle, is designed for optimal optical access while utilizing boundary conditions similar to those in a typical office environment. To simplify the flow, furniture is excluded from the setup. A heated manikin (no breathing effects) is introduced with seventeen heating zones set to the corresponding skin temperature of an average person. The combination of the ventilation and thermal buoyancy simulates the flows associated with displacement ventilation. Such a velocity database is useful both for CFD validation as well as turbulence model selection which was the initial thrust of the experiments. Research includes an analysis of three component Particle Image Velocimetry (PIV) measurements along the inlet of an isothermal ventilation system as it interacts with the buoyancy affects of the standing thermal occupant. From the PIV database, two-point correlations are computed and the integral lengths extracted. The propagation of length scales in both the streamwise and crosswise directions from the square foot floor inlet to occupant standing height are presented for consideration in addition to the turbulence moments of the flow.
Characteristics of Breaking Bow Waves Generated by a 2D+T Wave Maker
Authors: Shakeri Mostafa , Tavakolinejad Mohammadreza , Mayer Matthias , Duncan James H.
Published: September 2008

Ship bow waves simulated experimentally with a 2D+T wave maker were investigated experimentally. Wave profile measurements are presented for a range of equivalent full-scale ship speeds ranging from 16.5 to 27 knots. At the beginning of the wave maker motion, the water surface rises rapidly up the surface of the wave board which represents the hull of the equivalent ship model. The maximum rise height and the rate of rise increase with increasing equivalent ship speed. Later in the wave maker motion, this point of maximum water height moves away from the wave board and forms the primary crest in the wave pattern. This crest moves at a speed that is about 1.8 times the maximum speed of the wave board. At the higher speeds, this wave crest evolves into a strong plunging breaker with a jet that hits the water surface ahead of the breaker, creating a large splash and entraining large amounts of air. The temporal histories of various geometrical characteristics of the breaker are presented.
Prediction of the Fluid Induced Instability Force of an Axial Compressor
Authors: Kang Young-Seok , Kang Shin-Hyoung
Published: September 2008

Numerical calculations of a rotor row of a low speed axial compressor with an asymmetric tip clearance distribution were carried out. Asymmetric tip clearance induces blade loading and downstream pressure redistribution along the circumferential direction while upstream pressure field is maintained. At small flow coefficients, blade loading redistribution patterns are highly affected by upper 50% blade span region. High pressure difference at the small clearance region causes high blade loading at the small clearance region. On the other hand, at a high flow coefficient, blade loading redistribution is almost coincident with the asymmetric tip clearance distribution. In contrast to lower flow coefficients, the contribution of the lower 50% blade span region increases. A higher axial velocity induces a higher axial momentum, which delivers the upstream pressure field downstream without any circumferential redistribution. Blade loading redistribution due to increased axial momentum overcomes the redistribution caused by local tip clearance performance due to high pressure difference at the small clearance and becomes the dominant term of blade loading redistribution. As a result, the redistributed blade loading synchronizes with the tip clearance distribution and the strength of the blade loading redistribution increases as the flow coefficient increases.
Interface-Tracking Simulation of Two-Phase Flows by Phase-Field Method
Authors: Takada Naoki , Tomiyama Akio
Published: September 2008

The purpose of this study is to examine multi-physics computational fluid dynamics method, NS-PFM, which is a combination of Navier-Stokes (NS) equations with phase-field model (PFM) based on the free-energy theory, for interface-capturing/tracking simulation of two-phase flows. First, a new NS-PFM which we have proposed was applied to immiscible, incompressible, isothermal two-phase flow problems with a high density ratio equivalent to that of an air-water system. In this method, a Cahn-Hilliard equation was used for prediction of diffusive interface configuration. The numerical simulations demonstrated that (1) predicted collapse of two-dimensional liquid column in a gas under gravity agreed well with available data at aspect ratios of column = 1 and 2, and (2) coalescence of free-fall drops into a liquid film was successfully simulated in three dimensions. Second, we took heat transfer into account in another NS-PFM which solves a full set of NS equations and the van-der-Waals equation of state. Through a numerical simulation of a non-ideal fluid flow in the vicinity of the critical point, it was confirmed that the NS-PFM is applicable to thermal liquid-vapor flow problems with phase change.
Numerical Simulations of Air Flow in a Full Scale Clean Room Incorporating Fan Curves of Fan Filter Units
Authors: Chien Liang-Han , Huang Chia-Sung , Liao Wen-Jung , Chuah Yew-Khoh
Published: September 2008

This manuscript presents the air flow fields and pressure distributions of a full scale class 100 semiconductor clean room system using a computational fluid dynamics (CFD) model that incorporates flow resistances of various components in the air path. The fan-performance curves of fan filter unit (FFU), the pressure-velocity curves of the dry coil and the ULPA are included in the model. The pressure and velocity distributions of the present simulation are in reasonable agreement with the measurement in the real clean room system during operation. The numerical methodology of the present work is found to be a useful design tool of a FFU type clean room for the estimation of clean room pressure, velocity distribution and air exchange rate.
Base Flow Modification by Streamwise Vortices: Application to the Control of Separated Flows
Authors: Duriez Thomas , Aider Jean-Luc , Wesfreid Jose Eduardo
Published: September 2008

We first demonstrate the potential of cylindrical vortex generators to control the separation over a smoothly curved ramp in a low velocity hydrodynamic channel. We then focus on the influence of a row of four cylindrical vortex generators on a spatially growing flat plate boundary layer. Using two-component PIV measurements, we show how the boundary layer is modulated by counter-rotating streamwise vortices. We also analyze the 3D velocity field using non-linear perturbations to emphasize a clear modification of the base flow. This base flow modification, together with spanwise modulation, can explain the delay of the separation of the boundary layer over the curved ramp.
Optimization of a Fan Blade Cascade Using the Parametric Flow Solver Turb’Opty
Authors: Moreau S. , Aubert S. , Grondin G. , Ferrand P.
Published: September 2008

The parameterized CFD solver Turb’Opty™, based on a Taylor series expansion to high order derivatives of the solution of the discretized Navier-Stokes equations, has been successfully applied to the full geometric and flow parameterization of an engine cooling fan blade cascade. The coupling of a recently developed genetic algorithm and the post-processor Turb’Post™ has also yielded a multi-objective optimization of the original Valeo airfoil. A representative geometry of the Pareto front has then been prototyped and tested. Significant improvement of the lift coefficient has been obtained at all incidences. Comparisons with direct Turb’Flow™ cascade results have validated the accuracy of the parameterized solutions and shown the same trend as the free-jet measurements.
Investigation of Gas Properties for Combustion Products of Organic Fuels
Authors: Kim SooYong , Kovalevsky Valeri P. , Kim Dae-Seung
Published: September 2008

In making cycle performance calculation, it is first necessary to establish data relating to the properties of the working fluid of turbo-machinery. Because the composition of natural gas combustion products varies, along with the fuel chemistry, unique formulae for their gas properties do not exist, hence the calculation becomes more complex. Thermodynamic properties depend not only on composition of gases but also on assumptions concerning the change of composition during each process in which temperature, pressure or some other thermodynamic state functions may be shifting. In the present study, a calculation method of gas constants, heat capacity, enthalpy of dry, humid air and combustion products of organic fuel are studied. A theoretical base of thermodynamic properties of gas mixtures constructed on a model of ideal gas is formulated. The composition products are represented by the mixture of ideal gases, humid air and steam directly participating in the burning process and the products of stoichiometric combustion of any organic fuel. The developed calculation procedure is validated through comparison with tabulated data in open literatures and it presented satisfactory results. Recommendation for the application of the suggested method with restriction in relation to range of temperature for static and dynamic calculation is also given. It is supposed that the present method and its result can be used in the preliminary design stage of heat exchangers, high temperature gas turbine units and boilers.
Some Implications of Force Measurements for the Path Instability of Rising Bubbles
Authors: Shew Woodrow L. , Pinton Jean-Franc¸ois
Published: September 2008

The hydrodynamic forces on millimeter sized air bubbles undergoing zigzagging and spiraling path oscillations are deduced from precise experimental measurements of the bubble trajectory. We find that the lift force exhibits hysteretic dependence on bubble speed. We also observe an abrupt transition from rectilinear to oscillating path for increasing bubble size. These two facts suggest that a subcritical bifurcation may underlie the bubble path instability dynamics. We also measure unexpected dynamical changes in the drag experienced by the bubble which play a role in the path instability.
Deformation-Induced Lift on Receptor-Ligand Mediated Cell Adhesion to Substrates Explored by a 3-D Computational Fluid Dynamics Approach
Authors: Li Xiaoyi , Sarkar Kausik
Published: September 2008

The adhesion of cells to substrates is a critical step in plenty of biological events. The effects of cell deformation on the adhesion process have been investigated using a direct fluid dynamics simulation based on front-tracking method. A model including membrane elasticity and stochastic receptor-ligand binding has been developed. The study reveals a surprising effect of cell deformation. An asymmetry in upstream-downstream flow field due to cell deformation results in a hydrodynamic lift. The lift force counterbalances the shear torque and causes reduced contact area and reduced number of bond formed, and leads to cell detachment at relatively low shear rate. The finding of lift could be used to partially explain the shear threshold phenomenon occurring at small shear stresses.
Three-Dimensional Computational Modeling of Leukocyte Rolling and Adhesion
Authors: Khismatullin Damir B. , Truskey George A.
Published: September 2008

Recruitment of leukocytes into sites of acute and chronic inflammation is a vital component of the innate immune response in humans and plays an important role in cardiovascular diseases, such as ischemia-reperfusion injury and atherosclerosis. Leukocytes extravasate into the inflamed tissue through a multi-step process, which involves initial contact of a leukocyte with activated endothelium (tethering or capture), leukocyte rolling, firm adhesion, and transendothelial migration. We developed a computational fluid dynamics algorithm for fully three-dimensional transient simulations of multiphase viscoelastic problems. The algorithm was applied to model leukocyte rolling and adhesion in a parallel-plate flow chamber. In the model, the leukocyte is a viscoelastic cell with the nucleus located in the intracellular space and cylindrical microvilli distributed over the cell membrane. Leukocyte-endothelial cell interactions are mediated by cell adhesion molecules expressed on the tips of leukocyte microvilli and on endothelium. We show that the model can predict both shape changes and velocities of rolling leukocytes under physiological flow conditions. Results of this study indicate that viscosity of the cytoplasm is a critical parameter of leukocyte adhesion, affecting the cell’s ability to roll on endothelium.
Micro-Optical Sensors for Boundary Layer Flow Studies
Authors: Modarress Darius , Svitek Pavle , Modarress Katy , Wilson Daniel
Published: September 2008

This manuscript describes optical MEMS (or MOEMS)-based microsensors for near wall boundary layer flow and particle field analysis. The sensors have been developed to measure a variety of parameters including flow velocity, surface speed, skin friction, and particle sizing. The surface mounted sensors measure flow velocity and/or flow velocity gradients as close as 70 microns from the wall. The sensors have been successfully used in a number of filed tests and flow facilities at different Reynolds numbers. They have also been used on-board full-scale vehicles. These compact and embeddable sensors incorporate specially designed diffractive optical elements and use single-mode optical fiber or integrated diode lasers for illumination.
Electrophoresis in Nanochannels
Authors: Pennathur Sumita , Baldessari Fabio , Kattah Mike , Utz Paul J. , Santiago Juan G.
Published: September 2008

Micro- and nanofabrication technology enables the application of electrokinetics as a method of performing chemical analyses and achieving liquid pumping in electronically-controlled microchip systems with no moving parts. We are studying and leveraging the unique separation modalities offered by nanoscale electrokinetic channels. We report analytical, numerical, and experimental investigations of nanochannel electrophoretic transport and separation dynamics of neutral and charged analytes. Our study includes continuum-theory-based analytical and numerical studies of nanofluidic electrophoretic separation dynamics, as well as experimental validation of these models. We have used 40, 100, and 1,560 nm deep channels etched in fused silica to independently measure mobility and valence of small ions. We also use these devices to separate 10 to 100 base pair DNA in the absence of a gel separation matrix. The effective free-solution mobilities of the ds-DNA oligonucleotides measured in 1560 nm deep channel are consistent with reported literature values, while smaller values of the mobility were measured for 4o nm deep channels for the same charge-species. The goal of our work is to explore and exploit electrokinetic flow regimes with extreme scales of length and charge density.
Rotating Drum Half-Filled With Large Beads in Liquid: Fictitous-Domain Simulation and Experiment
Authors: Truong Hung V. , Wells John C. , Nguyen Anh
Published: September 2008

To numerically simulate “bedload transport” of sediment by a turbulent flow over an erodible bed, our group has been developing “fictitious domain” methods to handle dense-phase particulate flow in turbulent flow of liquid. We report on efforts to check our simulation method against experiment for a dense-phase particulate flow in liquid, namely a rotating drum half-filled with spherical particles. Overall agreement between experimental and simulated values of static and dynamic angle of repose is found to be quite satisfactory, both in air and in oil.
CFD Simulations of the Aeroacoustic Noise Generated by a Cavity Flow
Authors: Belamri T. , Egorov Y. , Menter F.
Published: September 2008

CFD simulations of the flow inside a cavity with a length to depth ratio (L/D) of 5 and a width to depth ratio (W/D) of 1 were performed using the 3D CFX code with the newly developed SAS (Scale Adaptive Simulation) turbulence model. The free-stream flow has a zero incidence and a Reynolds number of 1×106 (based on the cavity length). Two meshes were used with similar sizes and having different node distribution along the cavity regions. The former grid uses a constant step mesh along the cavity and the latter uses a stepwise mesh, which resolves much finer the shear layer at the start of the cavity. Predicted noise spectra at 10 monitor points, overall sound and Rossiter modes were compared to the experimental data. To complete this study, the effect of the sampling time was assessed. In general, the agreement between the compared results was very satisfactory showing the ability of the SAS model to predict both narrowband and broadband noise.
Microfluidics for Chemical Processing
Authors: Gardeniers Han J. G. E.
Published: September 2008

Microfluidic systems, and more specifically, microfluidic chips, have a number of features that make them particularly useful for the study of chemical reactions on-line. The present paper will discuss two examples, the study of fluidic behaviour at high pressures and the excitation and detection of nuclear magnetic resonance in a reaction mixture, both in nanoliter volumes.
Computational Analysis of Effective Microfluidic Mixing Utilizing Surface Heterogeneity Effects
Authors: Rahman M. A. , Heidrick T. , Fleck B.
Published: September 2008

The present work is a numerical simulation of electroosmotic flow (EOF) in a cylindrical microchannel with the variation of wall surface charge (ζ -potential) distributions. The 2D Navier-Stoke equation governing the velocity field and the pressure are solved numerically using the finite element method (FEM). The numerical results show that the distorted electroosmotic velocity profiles and various kinds of flow circulation resulting from the axial variation of the ζ. The influences of heterogeneous patterns of zeta potential on the velocity profile, and the induced pressure distribution are discussed in this paper. This study shows that using heterogeneous patterns of zeta potential over the channel can generate local flow circulations and hence provide effective means to improve the mixing within the microchannels.
Development of PIV/Interface Gradiometry to Handle Low Tracer Density and Curved Walls
Authors: Nguyen Chuong V. , Wells John C.
Published: September 2008

Despite the importance of near-wall flow, the well-known difficulties of applying PIV adjacent to walls have attracted little attention. In recent work, the authors have proposed and validated an extension of PIV, called “Interface Gradiometry” (PIV/IG), designed to directly measure the velocity gradient at a fixed wall. For a suitable choice of template height, combined with a sufficiently high density of flow tracers, the method was found to yield substantially more accurate results for wall velocity gradient than PIV/PID. This notwithstanding, the following restrictions and issues demand attention. For accurate measurements the template height must be sufficiently thin that the velocity increases only linearly therein; this is often a restrictive condition at practical Reynolds numbers. On the other hand, tracer concentration is often low adjacent to a wall, and it is often difficult to obtain enough tracers within templates satisfying the linearity condition. Finally, the method requires precise knowledge of the position of the wall. Accordingly, we present a technique that relies less critically on the choice of template height and on presumed wall position, while still exploiting most constraints that the wall imposes on the adjacent flow. Assuming the wall to be horizontal on the image, the basic method is, very simply, to perform 1D PIV on each horizontal line of pixels within the template. The principal “deliverable” at each point on the boundary is the wall-normal profile of horizontal velocity. In addition, our new work handles curved walls by transforming image segments into rectangles; this proposed enhancement should be significant in applications to real boundaries found industrially, or in biomedical imaging. The method is tested successfully on experimental images from a turbulent, locally recirculating flow over a sinusoidal wall.
CFD Combustion and Emission Formation Modeling for a HSDI Diesel Engine Using Detailed Chemistry
Authors: Golovitchev Valeri I. , Montorsi Luca , Rinaldini Carlo Alberto , Rosetti Angelo
Published: September 2008

In order to comply with current emissions regulations, a detailed analysis of the combustion and emission formation processes in the Diesel engines accounting for the effect of the main operating parameters is required. The present study is based both on 0D and 3D numerical simulations by compiling 0D chemical kinetics calculations for Diesel oil surrogate combustion and emission (soot, NOx) formation mechanisms to construct a φ-T (equivalence ratio - temperature) parametric map. In this map, the regions of emissions formation are depicted defining a possible optimal path between the regions by placing on the same map the engine operation conditions represented by the computational cells, whose parameters (equivalence ratio and temperature) are calculated by means of 3D engine modelling. Unlike previous approaches based on static parametric φ-T maps to analyze different combustion regimes and emission formations in Diesel engines, the present paper focuses on a construction of dynamic φ-T maps, in which the pressures and the elapsed times were taken in compliance with those calculated in the 3D engine simulations. The 0D chemical kinetics calculations have been performed by the SENKIN code of the Chemkin-2 library. In-cylinder conditions represented by computational cells with known φ and T are predicted using KIVA-3V code. When cells are plotted on the map, they identify the trajectories helping to navigate between the emissions regions by varying hardware and injection parameters. Sub-models of the KIVA-3V, rel. 2 code has been modified including spray atomization, droplet collision and evaporation, accounting for multi-component fuel vapor coupled with the improved versions of the chemistry/turbulence interaction model and new formulation of the combustion kinetics for the diesel oil surrogate (consisting in 70 species participating in 310 reactions). Simulations were performed for the HSDI 1.300 Fiat Diesel engine at optimized engine operating conditions and pilot injections. Finally, numerical results are compared with the experimental data on in-cylinder pressure, Rate of Heat Release, RoHR, and selected species distributions.
Utilizing a Cycle Simulation to Examine the Use of EGR for a Spark-Ignition Engine Including the Second Law of Thermodynamics
Authors: Caton Jerald A.
Published: September 2008

The use of exhaust gas recirculation (EGR) for a spark-ignition engine was examined using a thermodynamic cycle simulation including the second law of thermodynamics. Both a cooled and an adiabatic EGR configuration were considered. The engine was a 5.7 liter, automotive engine operating from idle to wide open throttle, and up to 6000 rpm. First, the reduction of nitric oxides is quantified for the base case condition (bmep = 325 kPa, 1400 rpm, φ = 1.0 and MBT timing). Over 90% reduction of nitric oxides is obtained with about 18% EGR for the cooled configuration, and with about 26% EGR for the adiabatic configuration. For constant load and speed, the thermal efficiencies increase with increasing EGR for both configurations, and the results show that this increase is mainly due to decreasing pumping losses and decreasing heat losses. In addition, results from the second law of thermodynamics indicated an increase in the destruction of availability (exergy) during the combustion process as EGR levels increase for both configurations. The major reason for this increase in the destruction of availability was the decrease in the combustion temperatures. Complete results for the availability destruction are provided for both configurations.
First and Second Law Analyses of a Spark-Ignition Engine Using Either Isooctane or Hydrogen: An Initial Assessment
Authors: Caton Jerald A.
Published: September 2008

The use of either hydrogen or isooctane for a spark-ignition engine was examined using a thermodynamic cycle simulation including the second law of thermodynamics. The engine studied was a 5.7 liter, automotive engine operating from idle to wide open throttle. The hydrogen or isooctane was assumed premixed with the air. Two features of hydrogen combustion that were included in the study were the higher flame speeds (shorter burn durations) and the wider lean flammability limits (lean equivalence ratios). Three cases were considered for the use of hydrogen: (1) standard burn duration and an equivalence ratio of 1.0, (2) a shorter burn duration and an equivalence ratio of 1.0, and (3) a shorter burn duration and variable, lean equivalence ratios. The results included thermal efficiencies, other performance metrics, second law parameters, and nitric oxide emissions. In general, for the cases with an equivalence of 1.0, the brake thermal efficiency was slightly lower for the hydrogen cases due to the higher temperatures and higher heat losses. For the variable, lean equivalence ratio cases, the thermal efficiency was higher for the hydrogen case relative to the isooctane case. Due to the higher temperatures, the hydrogen cases had over 50% higher nitric oxide emissions compared to the isooctane case at the base conditions. In addition, the second law analyses indicated that the destruction of availability during the combustion process was lower for the base hydrogen case (11.2%) relative to the isooctane case (21.1%).
Development of the Waukesha 16V150 LTD Advanced Power Generation Engine
Authors: Reinbold Ed , Mather Daniel
Published: September 2008

Waukesha Engine has developed an advanced power generation engine using technologies that were developed as part of the Department of Energy-Advanced Reciprocating Engine Systems (ARES) program. The engine uses lean-burn technologies for high efficiency, and low NOx emissions. The technical goals for the ARES program were 50% Brake Thermal Efficiency (BTE) and 0.075 g/kW-hr NOx emissions (with aftertreatment). The goals for the Waukesha Engine Phase 1 Advanced Power Generation (APG) engine are 42% Brake Thermal Efficiency (BTE) and 0.75 g/kW-hr (1.0 g/Bhp-hr) NOx emissions, capable of 0.075 g/kW-hr (0.1 g/Bhp-hr) with aftertreatment. The barriers and technical paths applied to achieve this performance are discussed in this paper.
Fuel Consumption and Exhaust Emissions From a 1,125 kW Multiple Genset Switcher Locomotive
Authors: Honc Randell L. , Fritz Steven G. , Schell Michael B. , Tarnow Andrew , Bennett Adam
Published: September 2008

Conventional switcher or shunting locomotives in North America are powered by a single Electro-Motive Diesel (EMD) 12 or 16 cylinder 645E engine which operate at eight distinct power levels, plus idle, at engine speeds ranging from 250 to 900 rpm, and power ratings of 1125 to 1500 kW. The individual power (notch) settings are weighted according to an established duty cycle to obtain overall fuel consumption and exhaust emission rates. Recently introduced locomotive power systems utilize multiple smaller displacement non-road diesel engines packaged as individual generator sets to obtain a cleaner and more efficient locomotive. This paper compares exhaust emissions and fuel consumption from a conventional switcher locomotive with a single large displacement engine to that of a repowered locomotive utilizing three 345 kW generators.
Measuring the Changing Composition and Mass of Evaporating Fuel Films
Authors: Kelly-Zion Peter , Jelf Catherine , Pursell Christopher , Oxley Susan
Published: September 2008

When a fuel spray impinges on an interior surface of an engine, a thin liquid film can form. The relatively slow evaporation of the film has been shown to be a cause of increased pollutant emissions and reduced engine performance. To improve the understanding of how fuel films affect engine emissions and performance, a research program was initiated to study the physical processes involved in the evaporation of films composed of mixtures of hydrocarbons. The specific goal of the research reported here is to develop a method of simultaneously measuring the mass and composition of evaporating films. This method enables one to compute the evaporation rate of each component in the film. To our knowledge, these composition measurements are the first direct, time-resolved measurements of the changing composition of an evaporating liquid film composed of multiple volatile components. Mass and composition of evaporating liquid films were measured quantitatively using a Fourier transform infrared spectrometer (FT-IR). Evaporation rates for pure solvents and mixtures were determined through a calibration of the FT-IR measurements and these results were validated by measurements acquired with an analytical balance. The FT-IR also measured compositional changes for bi-component mixtures during the evaporation process. Three of the hydrocarbon solvents studied were hexane, cyclohexane, and 3-methylpentane. These were chosen for their similarities in molecular weight and physical properties as well as their comparatively unique infrared absorption spectra. Isooctane was also used because of its prevalence as a gasoline substitute in many engine studies and because of its slow evaporation rate compared to the smaller hydrocarbons. Solvents were studied individually and in various mixtures. Based on these preliminary results the method developed here is expected to be an important tool for studying the transport processes in an evaporating film.
Design and Analysis of the Waukesha APG1000 Engine
Authors: Nicoson Rodney , Knudsen Julian
Published: September 2008

Waukesha Engine, in cooperation with the Department of Energy, has designed a new high efficiency natural gas engine designed specifically for the power generation market. The APG1000 (Advance Power Generation) engine is capable of achieving 1 MW output at 42% thermal efficiency and less than 1 g/bhp-hr Nox. A design method using modern tools such as 3-D modeling, rapid prototyping and computer simulation have, in a large part, contributed to the success of this engine. This paper discusses the methodology and tools used in the design of the APG engine.
Innovative Lift Direct Command to Inner Hydraulic Circuit Injector Comparison for Diesel Engines
Authors: Allocca Luigi , Alfuso S. , Montanaro A. , Valentino G. , Lolli M.
Published: September 2008

In this paper a comparative investigation between two different injectors for Common Rail diesel apparatus has been carried out in terms of transient response and spray pattern for different injection strategies. Performances of an innovative Magneti Marelli (MM) gasoline derived injector have been evaluated against the Bosch generation injectors for multiple strategies. Both injectors have operated on an automotive apparatus controlled by a Programmable Electronic Control Unit to set injection strategies in terms of pulses number, duration and dwell time. The working mode of the two injectors is completely different: the Bosch injector is activated by the inner fuel hydraulic circuit while the Magneti Marelli one operates a direct control of the needle lift through the solenoid currents. The Bosch nozzle characteristics are 5 holes, 150° spray angle, and 0,13 mm diameter. The MM injector main characteristics are low hydraulic losses, simple component structure and ready use of the fuel at the nozzle opening being able to control small fuel flow rates (0.1 mg/str) in the injection pressures range 20–70 MPa. The geometry of the nozzle is quite similar to the Bosch one being a 5 hole, 150° spray angle, 0.12 mm diameter. Single, pilot+main and pilot+split main strategies have been explored for the two injectors at 50 and 60 MPa injection pressures investigating the spray behavior for two amounts of injected fuel (5.0 and 6.5 mg/str). The systems have been characterized in terms of injected fuel rate as well spatial and temporal behavior of the emerging jets from the nozzle. Images of the spray have been collected by a synchronized CCD camera at different time from the start of injection. The jets have evolved in an optically accessible high pressure vessel at ambient temperature as well in an optically accessible single-cylinder 2-stroke Diesel engine extracting the fuel spray parameters from the collected images applying a digital processing techniques. Due to the diverse mechanism of the injector actuation, a different temporal and spatial fuel distribution has been registered for the two apparatuses. These could strongly influence the air/fuel mixture formation and combustion process with effect on the emissions. Preliminary engine tests performed on a light duty direct injection diesel engine, equipped with the MM injector, have highlighted the potential of the MM injector to handle acceptable engine performances.
Design and Performance of a Controlled Turbocharging System on Marine Diesel Engines
Authors: Vlaskos Ioannis , Codan Ennio , Alexandrakis Nikolaos , Papalambrou George , Ioannou Marios , Kyrtatos Nikolaos , Boom Rick
Published: September 2008

The paper describes the design process for a controlled pulse turbocharging system (CPT) on a 5 cylinder 4-stroke marine engine and highlights the potential for improved engine performance as well as reduced smoke emissions under steady state and transient operating conditions, as offered by the following technologies: • controlled pulse turbocharging, • high pressure air injection onto the compressor impeller as well as into the air receiver, and • an electronic engine control system, including a hydraulic powered electric actuator. Calibrated engine simulation computer models based on the results of tests performed on the engine in its baseline configuration were used to design the CPT components. Various engine tests with CPT under steady state and transient operating conditions show the engine optimization process and how the above-mentioned technologies benefit engine behavior in both generator and propeller law operation.