bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Waves, Secondary Instability and Transition in a Three-Dimensional Boundary Layer
Authors: Pier Benoiˆt
Published: September 2008

The present investigation addresses the general problem of three-dimensional boundary layers, produced whenever a solid object rotates surrounded by a viscous fluid, or when an obstacle is obliquely displaced with respect to the outer fluid. This type of flow is encountered in a variety of configurations of practical interest: centrifugal pumps, fans, turbomachinery elements, swept aircraft wings, computer hard disks, oil well drilling devices... All of these flows are well known to display strong instabilities that rapidly lead to a turbulent re´gime. Despite intensive work and recent advances [1] however, no full understanding of the turbulent breakdown process has yet been achieved.
Experimental Investigation and Visualization of Helical Structures in a Novel Swirling Jet
Authors: Regunath G. , Tesar V. , Zimmerman W. B. J. , Hewakandamby B. N. , Russell N.
Published: September 2008

This paper describes an experimental study carried out to investigate the dynamics of helical structures in an unforced swirling jet and in a forced swirling jet that is excited by acoustic methods. An experimental rig that consists of a novel swirling jet and acoustic generation chamber is utilized to study the characteristics and mutual interaction of helical structures. For the excited jet, the helical structures are acoustically triggered in the jet-mixing layer. The acoustic excitation is applied transversely by an array of eight loudspeakers using radial wave-guides. The loudspeakers are driven by harmonic acoustic signals mutually phase shifted by a quarter of the period between each two neighbors so as to act in effect to produce two rotating waves. To generate swirl in the flow, novel swirl generators are utilized. The approach is to substitute the usual vanes set at an angle relative to the incoming flow by fixed vanes at a zero angle of attack, with the flow deflection based on super-circulation produced by the Coanda effect. The particle image velocimetry method was employed to analyze, quantify and visualize the flow field.
Planate Conducting Polymer Actuator and Its Application
Authors: Fuchiwaki Masaki , Tanaka Kazuhiro , Kaneto Keiichi
Published: September 2008

We propose a planate conducting polymer actuator which can transform only its central part locally and a micro pump using its actuator as a drive source. We have developed a planate conducting polymer actuator based on polypyrrole and two types of acids, such as p-phenol sulfonic acid and dodecylbenzene sulfonic acid, by electrodeposition. Its structure was patterned bimorph structure with anion-driven, cation-driven and bimorph layers. The planate conducting polymer actuator could deform only its central part locally. And, we have proposed a micro pump using the planate conducting polymer actuator as the drive source. The water level in the flow channel of micro pump shows the reciprocating motion measuring ±2 mm in accordance with the oscillation of the bimorph conducting polymer actuator which was approximately 28 μl/min. The oscillating volume can be controlled by the application of electrochemical potential and its scan rate applied to the actuator.
Numerical Simulation of the Unsteady Flow Patterns in a Small Squirrel-Cage Fan
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Gonza´lez-Pe´rez Jose´ , Pereiras-Garci´a Bruno
Published: September 2008

In this work, a numerical simulation on the main flow features in a squirrel-cage fan, used in automotive air conditioning units, has been carried out. A 3D unsteady model has been developed for the entire machine. The flow in this geometrical model has been solved using the commercial code FLUENT®. Some of the analyzed features are the performance curves, the flow distribution over the different aspiration sections, the pressure and velocity distributions in selected surfaces, and the forces on the blades and on the whole impeller. The numerical results have been compared with the available experimental data, showing a reasonable good agreement.
Cross-Flow Ultrafiltration Scaling Considerations
Authors: Duignan Mark R. , Lee Si Y.
Published: September 2008

One legacy of the nuclear age is radioactive waste and it must be stabilized to be stored in a safe manner. An important part of the stabilization process is the separation of radioactive solids from the liquid wastes by cross-flow ultrafiltration. The performance of this technology with the wastes to be treated was unknown and, therefore, had to be obtained. However, before beginning a filter study the question of experimental scale had to be addressed. Of course, carrying out experiments using full-size equipment is always ideal, but rarely practical when dealing with plant size processes. Flow loops that will handle millions of liters of slurries, which are either highly caustic or acidic, with flow rates of 10,000 lpm make full-scale tests prohibitively expensive. Moreover, when the slurries happen to be radioactive such work is also very dangerous. All of these considerations lend themselves to investigations at smaller scales and in many situations can be treated with computational analyses. Unfortunately, as scale is reduced it becomes harder to provide prototypic results and the two and three phase multi-component mixtures challenge accurate computational results. To obtain accurate and representative filter results two smaller scale filters were chosen: 1. Small-scale – would allow the testing with actual radioactive waste samples and compare results with simulated wastes that were not radioactive. For this scale the feed tank held 6 liters of waste and it had a single cross-flow filter tube 0.61 m long. 2. Pilot-scale – would be restricted to use simulated non-radioactive wastes. At this larger scale the feed tank held 120 liters of waste and the filter unit was prototypic to the planned plant facility in pore size (0.1 micron), length (2.29 m), diameter (0.0127 m inside and 0.0159 m outside diameter), and being multi-tubed. The small-scale apparatus is convenient, easy to use, and can test both radioactive and non-radioactive wastes; therefore, there is a larger database than at the pilot scale. In fact, the small-scale data are very useful to compare actual waste to simulated waste filter performance to validate a simulant, but data availability does not mean they accurately represent full-scale performance. Results indicate that small-scale filter fluxes to be significantly higher that those at the pilot scale. In an attempt to study the difference in filter performance at the two scales an experiment was done that used exactly the same simultant which was created at the same time so that issues of composition and aging would not compromise the results. This paper will discuss those experimental results, as well as those from a computational fluid dynamics model to better understand the small-scale limitations.
Progress in Modeling Injector Cavitating Flows With a Multi-Fluid Method
Authors: Wang De Ming , Greif David
Published: September 2008

A finite volume, pressure based semi-implicit algorithm is developed for solving a multi-fluid system of any number of phases with strong coupling between the phases in mass, momentum and energy transfer. The mass transfer from liquid to vapor due to cavitation is modeled based on a single bubble dynamics (Rayleigh-Plesset equation). In order to model the vapor phase of variable size distribution, or polydispersion, the transport equations of bubble number density and interfacial area are derived from taking the moments of the PDF equation in phase space. The modeling of the result equations are effected through consideration of breakup and coalescence. The k-zeta-f turbulence model is adopted which is found to be particularly effective for predicting near wall effects on the turbulence level. Validation efforts are presented in which comparison with available measurement data are made for a number of cases including constricted channel flow with sharp inlet (I-channel), with smooth inlet (Y-channel), a flash-boiling cavitation set-up, and an actual injector set-up.
Performance Evaluation of a Regenerative Blower for Hydrogen Recirculation Application in Fuel Cell Vehicles
Authors: Kim Young-Hoon , Kang Shin-Hyoung
Published: September 2008

Regenerative blowers are used for hydrogen gas recirculation application in fuel cell vehicles. In this paper we discuss the performance of theoretical models that describe the complex three dimensional flows in regenerative blowers. A one-dimensional performance prediction code is developed based on theoretical models and loss models. Numerical calculation is also performed using a commercial CFD code to analyze the three dimensional flows in a regenerative blower. The results of numerical analysis are used to evaluate the performance of the designed blower and improve the accuracy of performance prediction by correcting the loss models. The results of performance predictions are compared with measured data of a prototype regenerative blower to validate the one-dimensional performance prediction method.
Micro-Actuated Delta Wings Induced Control of Boundary Layer Separation
Authors: Lori Augusto , Xanthos Savaas , Ardebili Mahmoud , Andreopoulos Yiannis
Published: September 2008

Control of boundary layer separation has been investigated employing an array of micro-actuated delta winglets. The flow with the array is simulated computationally in an initially two-dimensional boundary layer, which is subjected to a Favorable Pressure Gradient (FPG) that accelerated the flow substantially, followed by an Adverse Pressure Gradient (APG) where the flow decelerated, the two successive distortions cause a flow separation in the boundary layer developing on the opposite wall of the wind tunnel. The simulations capture vortices formed by the impulsive motion of the delta wings. The vortices are part of recirculating zone in the wake of the actuators, which as they advect downstream, bring high momentum fluid into the near wall region of a separated flow. Preliminary results indicate micro-actuated delta wings array affect boundary layer separation favorably.
A Two Zone Interfacial Shear Stress and Liquid Film Velocity Model for Vertical Annular Two-Phase Flow
Authors: Hurlburt Evan T. , Fore Larry B. , Bauer Richard C.
Published: September 2008

The standard approach in estimating the interfacial shear between the vapor and the liquid film in annular two-phase flow is to include the effect of waves using a two-phase friction factor. This has been successful for low pressure annular flows in large hydraulic diameter ducts (wave heights ≪ H/2). It does not, however, work well for high pressure flows in smaller hydraulic diameter ducts (wave heights ∼ H/2). This suggests the need for a more detailed approach to incorporate wave effects in annular flow.
Visualization of the Heat Transfer Enhancement During Condensation in a Microfin Tube
Authors: Cavallini Alberto , Del Col Davide , Doretti Luca , Mancin Simone , Rossetto Luisa , Zilio Claudio
Published: September 2008

Microfins tubes are largely used in refrigeration industry for in-tube refrigerant condensation, because of the heat transfer enhancement when compared to equivalent smooth tubes under the same operating conditions. But not much evidence about the effect of microfins on the condensation flow patterns is available in the open literature. There is agreement in the open literature that the mechanisms of heat transfer are intimately linked with the prevailing two-phase flow regime. The present authors have recently measured the heat transfer coefficient during condensation of R410A in a microfin tube. The heat transfer enhancement in this tube can be experimentally evaluated by comparing those coefficients to the ones measured by Cavallini et al. (2001) in a plain tube, at the same operating conditions. The same operative conditions (saturation temperature, vapor quality and mass flux), occurring during the heat transfer measurements, were reproduced in a different section for visualization of flow patterns during condensation of R410A. The flow visualization has been carried out both in the plain tube and in the microfin tube. The objective of the present paper is to present the heat transfer enhancement during condensation of R410A and to show the flow visualized at the same operating condition for both the smooth and the microfin tube, aiming to link the heat transfer enhancement to the flow pattern variation.
Influence of Wave Shape on the Impact of Shallow-Water Waves on Vertical Walls
Authors: Zanzi Claudio , Go´mez Pablo , Palacios Julia´n , Lo´pez Joaqui´n , Herna´ndez Julio
Published: September 2008

A numerical study of the impact of shallow-water waves on vertical walls is presented. The air-liquid flow was simulated using a code for incompressible viscous flow, based on a local level set algorithm and a second-order approximate projection method. The level set transport and reinitialization equations were solved in a narrow band around the interface using an adaptive refined grid. The wave is assumed to be generated by a plunger which is accelerated in an open channel containing water. An arbitrary Lagrangian-Eulerian method was used to take into account the relative movement between the plunger and the end wall of the channel. The evolution of the free surface was visualized using a laser light sheet and a high-speed camera, with a sampling frequency of 1000 Hz. Several simulations were carried out to investigate the influence of the shape of the wave approaching the wall on the relevant quantities associated with the impact. The wave shape just before the impact was changed varying the total length of the channel. The results are compared with experimental results and with results obtained by other authors.
Digital Holographic Spray Analyzer
Authors: Miller B. , Sallam K. A. , Lin K.-C. , Carter C.
Published: September 2008

Advanced spray diagnostics are needed for studying the formation of drops in a variety of natural and technological spray processes, e.g. water falls, bow waves of ships, and many types of commercial spray atomizers, among others. Of interest is the dense-spray near-injector region which is typically opaque for spray diagnostics such as phase Doppler particle analyzers (PDPA). This is unfortunate because primary breakup processes that control spray size and velocity distributions occur in this optically challenging region. The present setup; digital holographic spray analyzer, allows the probing of dense spray regions and provides the user with droplet sizes and velocities measurements in three dimensions. The setup is based on typical in-line holography except that the holographic film is replaced with a CCD sensor. The actual process of capturing the hologram is a relatively simple process only requiring a laser, optics to form a collimated beam, and a digital camera. The hologram is then stored digitally and reconstructed numerically with a reconstruction program. After reconstructing the hologram in many different planes, the droplet size distribution is measured. In addition droplet velocities are measured by means of double pulsed exposure configuration and PIV program. All these processes can be automated which is the strength of this technique. The output is a three dimensional map of droplets locations, sizes, and velocities. This digital holographic spray analyzer was tested by measuring droplet sizes inside the dense spray created by an aerated injector subjected to a subsonic crossflow typical of test condition encountered in ramjet engine.
Diffusion of Slightly Buoyant Droplets in Isotropic Turbulence
Authors: Gopalan Balaji , Malkiel Edwin , Katz Joseph
Published: September 2008

We study the diffusion of slightly buoyant droplets in isotropic turbulence using High Speed Digital Holographic PIV. Droplets (Specific Gravity 0.85) are injected in the central portion of an isotropic turbulence facility with weak mean flow. Perpendicular digital inline holograms are recorded in a 37 × 37 × 37 mm3 region of interest using two high speed cameras. Data are recorded at 250 frames per second (2000 frames per second is the maximum possible frame rate). An automated program is developed to obtain two dimensional tracks of the droplets from two orthogonal images and match them to get three dimensional tracks. Cross correlation of droplet images are used for measuring their velocities. The time series are low pass filtered to obtain accurate time history of droplet velocities. Data analysis determines the PDF of velocity and acceleration in three dimensions. The time history also enables us to calculate the three dimensional Lagrangian velocity autocorrelation function for different droplet radii. Integration of these functions gives us the diffusion coefficients. For shorter time scales, when the diffusion need not be Fickian we can use the three dimensional trajectories to calculate the generalized dispersion tensor and measure the time elapsed for diffusion to become Fickian.
Turbulence Characteristics in a Rushton Stirring Vessel: A Numerical Investigation
Authors: Vlachakis V. N. , Brady M. R. , Yoon R. H. , Telionis D. P. , Vlachos P. P.
Published: September 2008

Results from simulations using FLUENT (a commercial CFD package) are compared with Time Resolved Digital Particle Image Velocimetry (DPIV) for baseline configurations in order to validate and verify the fidelity of the computations. Different turbulent models are used in this study in order to determine which one is the most appropriate. Subsequently a parametric analysis of the flow characteristics as a function of the clearance height of the impeller from the vessel floor is performed. Results are presented along planes normal and parallel to the impeller axis, displaying velocity vector fields and contour plots of vorticity turbulent dissipation and others. Special attention is focused in the neighborhood of the impeller region and the radial jet generated there. The present results provide useful information for the design of the mixing process as well as for more accurate estimations in future work.
Measurement of Turbulent Mixing Along Slope in Stratified Flow
Authors: Chen Jun , Odier Philippe , Rivera Michael , Ecke Robert
Published: September 2008

The mixing phenomenon of ocean currents, which have different densities as well as velocities, are important to ocean dynamics and global climate modeling. One example is the outflow of the Greenland-Iceland-Norwegian Seas, where dense Arctic water overflows a ridge and spills downslope in a density-driven plume until it reaches the deep abyss of the Atlantic Ocean. On the way down it mixes with ambient water of different temperature and salinity. This process affects the global thermohaline circulation, which is a significant element in changes of the global climate. Laboratory experiments are conducted to investigate this problem. A turbulent jet is introduced into a water tank along an inclined plate. The density difference between the jet and the tank water produces a stably stratified boundary current. Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) are applied to obtain simultaneous measurement of velocity field and density field along the slope at different downstream locations. On-going efforts are also discussed.
Control of Separated Boundary-Layer on Subsonic Airfoil Using Vortex Generator Jet Devices
Authors: Kourta A. , Petit G. , Courty J. C. , Rosenblum J. P.
Published: September 2008

The control of subsonic high lift induced separation on airfoil may improve the flight envelope of current aircraft or even simplify the complex and heavy high-lift devices on commercial airframes. Until now, synthetic jets have proved a really interesting efficiency to delay or remove even leading-edge located separated areas on high-lift configuration but are not efficient for real scale aircrafts. In case of pressure-like separation (i.e. from trailing-edge), synthetic jets can be replaced by so the called “Vortex Generator Jets” which create strong longitudinal vortices that increase mixing in inner boundary layer and consequently the skin friction coefficient is increased to prevent separation. In this study, numerical simulations were undertaken on a generic three dimensional flat plate in order to quantify the effect of the longitudinal vortices on the natural skin friction coefficient. Both counter and co-rotative devices were tested at different exhaust velocities and distances between each others. Finally co-rotative vortex generators jets were tested on a three dimensional generic airfoil ONERA D. Results show a delay of the separation occurence but this solution does not seem to be as robust as synthetic jets. The study of jets spacing with respect to the efficiency of the devices shows a maximum for a given ratio of spacing to exhaust velocity.
Uncertainty Estimation for Numerical Solutions of Wall Bounded Turbulent Flows
Authors: Elizalde-Blancas Francisco , Celik Ismail , Pakalapati Suryanarayana
Published: September 2008

In this study numerical solutions are presented for a steady state, incompressible, 2-D turbulent flow near a wall. For this specific problem a manufactured (exact) solution was provided by the organizers of the 2006 Lisbon Workshop [6]. With the help of manufactured solution, assessment of the true error and other relevant uncertainty measures are possible. The calculations were performed using the commercial flow solver FLUENT along with some user defined functions to define source terms and velocity profiles at boundaries. Though the flow regime is turbulent; the numerical solution is carried out for pseudo-laminar flow. This was done in order to avoid the errors implicit in turbulence models. The transformation from turbulent to laminar flow was done by defining a momentum source term which precludes the pressure gradient term. A detailed grid convergence analysis was performed. Using three-grid triplets the limiting values of the variables solved as the grid size tends to zero were calculated using different extrapolations. The L2 norms of the true error obtained from various extrapolations are assessed. These results exhibit solution convergence as the grid size decreases. It was also shown that cubic spline extrapolation perform the best among the methods considered.
Growth and Dissolution of Encapsulated Microbubble Used in Ultrasound Contrast Imaging
Authors: Jain Pankaj , Sarkar Kausik
Published: September 2008

Steady dissolution of a bubble with two gases and a permeable shell has been modeled. At first the shell is modeled without elasticity. Factors such as permeability of the shell, surface tension, mole fraction of the osmotic agent, gas concentration in the bulk have been varied to study the growth and the time scale for dissolution of the bubble. It has been found that the inclusion of shell elasticity also plays a vital role in the growth and dissolution of the bubble.
Three-Dimensional Plasma-Based Stall Control Simulations With Coupled First-Principles Approaches
Authors: Gaitonde Datta V. , Visbal Miguel R. , Rouy Subrata
Published: September 2008

Numerical simulations are employed to understand the mechanisms by which asymmetric dielectric barrier discharges operating at radio frequencies reduce or eliminate stall. The specific focus is on a NACA 0015 wing section at a nominal Reynolds number of 45,000 and 15 degree angle-of-attack. The body force is obtained separately from both phenomenological and first-principles based models. To overcome the daunting complexity of the latter approach, a procedure to couple unsteady force fields obtained from multi-fluid models to very high-fidelity implicit large-eddy simulations is developed, implemented and evaluated for a 5kHz signal. The paper discusses results with both approaches to understand the effect of Reynolds number, angle of attack, actuator strength and location as well as unsteadiness of actuation through radio frequency excitation and duty cycle variation. The results are assimilated in the context of the combined impact of near wall momentum enhancement and transition to turbulence. It is shown that force fluctuations at radio-frequencies result in the development of a rich turbulence structure downstream of actuation. These observations, as well as details of the acoustic signal, cannot be obtained from the simplified steady force model. For higher Reynolds numbers and relatively lower actuation forces, mechanisms that enhance turbulence development are the dominant consideration. These include not only radio-frequency force variations, but also streamwise vorticity generation through edge effects associated with finite-span actuation and wide-spectrum input associated with switch-on/switch-off inherent in duty cycles.
High-Order Computational Techniques for Unsteady Vortical Flows Over Delta Wings
Authors: Gordnier Raymond E. , Visbal Miguel R.
Published: September 2008

A high-order computational method for the highly unsteady, complex vortical flows over delta wings is presented. A sixth-order compact difference scheme with an eighth-order low pass filter is used to solve the Navier-Stokes equations. Two approaches to turbulence modeling are investigated. The first scheme is an implicit LES (ILES) method which exploits the high-order accuracy of the compact difference scheme and uses the discriminating higher-order filter to regularize the flow. The second approach is a new hybrid RANS/ILES method which employs a standard k–ε model in regions where the grid resolution is unable to capture the turbulent behavior, and transitions to the ILES method in the vortical flow region where large scale turbulent structures are resolved. Computational simulations have been performed for a 50° sweep delta wing at 15° angle of attack and a moderate Reynolds number, Re = 2 × 106. Solutions employing the two turbulence models are evaluated on a baseline grid. A fine mesh computation has been performed for the ILES approach to investigate the impact of mesh resolution on this scheme. Computed results are also compared with the limited experimental measurements available. Computations exploring the control of the vortical flows above a swept delta wing by use of a dialectric-barrier-discharge actuator are also presented. With the actuator located near the apex, significant movement of the vortex breakdown location and a dramatic transformation of the shear-layer sub-structures are demonstrated.
Enhancement of the Completion Efficiency of Perforation Tunnels in Petroleum Wells
Authors: Rahman M. A. , Heidrick T. , Fleck B. , Koksal M.
Published: September 2008

The objective of perforating is to maximize well productivity by establishing good connectivity between the wellbore and formation. The conventional method of perforation — perforation by shooting (PS) — cannot achieve expected wellbore productivity due to a region of reduced permeability around the perforation tunnel. In this study, it has been established that permeability is decreased in the range of 30%–75% due to the implementation of the PS technique compared to the openhole completion. As a result, a new perforation technique — perforation by drilling (PD) — has been proposed in this paper. To simulate a perforated completion, cylindrical sand samples (0.0572 in OD) consolidated with cement with varying porosity were prepared. These samples were perforated (0.0136 m ED) by the PS, PD and Casting techniques. Perforations created by the Casting techniques are considered the ideal, openhole perforation tunnel. Fluid flow rates and differential pressure across the perforated samples were measured for three different types of samples using “Geotechnical Digital System” triaxial testing set-up. Fluid flow rates with changing differential pressure and finally pressure build-up data with time indicates the PD technique can achieve better wellbore productivity compared to the PS technique. Results indicate that at 100 kPa differential pressure the PS, PD and Casting techniques can achieve 0.20 mL/s, 0.65 mL/s and 1.00 mL/s fluid flow rates respectively across a sample.
Static and Dynamic Analysis of Annular Seals
Authors: Arghir Mihai , Frene Jean
Published: September 2008

This work is an overview of theoretical approaches used for estimating the characteristics of straight or grooved annular seals. The flow in annular seals is dominated by inertia forces. The goal of the static analysis is to describe the relation between the pressure difference across the seal and the (mass) flow rate. The presentation introduces different approaches of the static problem (analytic, simplified–“bulk flow” and CFD) and underlines the main difficulties in analysing annular seals. The forces on an eccentric rotor are described as a superposition between three effects (Lomakin, viscous and Bernoulli forces). This approach is then used to describe the dynamic characteristics of the seal for a rotor whirling around its centred position. The specific aspects that compressibility adds to gas annular seals analysis are next discussed, with its most important consequence, the flow choking in the exit section. Finally, some recent findings concerning the analysis of textured stator annular seals are presented. The results show that the presence of textures engenders stator and rotor friction coefficients obeying different laws. The use of these new friction coefficients in the bulk-flow equations enables to match the values of the experimental dynamic coefficients. A discussion about the further needs (development and research) in annular seals analysis is carried out at the end of this work.
Numerical Simulation of a Low Pressure Turbine Blade Employing Active Flow Control
Authors: Galbraith Marshall C. , Kasliwal Amit , Ghia Kirti , Ghia Urmila
Published: September 2008

High altitude aircraft experience a large drop in the Reynolds number (Re) from take off conditions to cruise conditions. It has been shown in previous research performed by Simon and Volino [1] that this reduction in Re number causes the flow inside the turbine cascades to become laminar, and separate more readily on the suction side of the turbine blade. This boundary-layer separation greatly reduces the efficiency of the turbine and aircraft engine as a whole, and therefore is undesirable. To prevent this loss of efficiency, research will be pursued for active and passive means to delay and/or eliminate the flow separation. Lake et al. [2] used passive boundary layer trip, dimples, and V-grooves in an extensive study to reduce separation on the Pak-B turbine blade. Although these passive techniques were able to reduce the separation at fixed Re numbers, an active flow control method is needed for more efficient separation reduction over a range of Re numbers. Currently, researchers are investigating several different active flow control devices, including pulsating synthetic jets, vortex generator jets (VGJ), and moving protuberances. The proposed study intends to further investigate the mechanism of flow control via synthetic jets, which alternate between suction and blowing, on a low pressure turbine blade utilizing a Large Eddy Simulation (LES) Computational Fluid Dynamics (CFD) solver. Optimum values of the associated parameters such as jet angle, blowing ratio, frequency, duty cycle, etc., of the synthetic jets will be determined. However, before investigation of the effectiveness of synthetic jets, the CFD simulation will be validated with experimental data on VGJ. A description of the implementation is presented along with preliminary results.
Synergy Mechanism in Combined Polymer and Microbubble Drag Reduction: Decreased Polymer Diffusion
Authors: Petrie Howard L. , Fontaine Arnold A. , Moeny Michael J. , Deutsch Steven
Published: September 2008

Drag reduction (DR) experiments with combined micro-bubble and polymer solution injection were conducted in a water tunnel at the ARL/Penn State. Previous research has shown that gas injected upstream of polymer produced higher levels of DR than expected based on DR levels observed with the independent injection of micro-bubbles or polymer alone. This synergy between the two injection processes was speculated to have resulted from a decrease in the diffusion rate of injected polymer away from the surface by the effects of the micro-bubbles. The slowed polymer diffusion should extend the length of the zone where large polymer DR occurs. In the current work, a confocal-style laser induced fluorescence based probe was developed and used to measure the wall concentration of injected polymer solutions and injected water with and without upstream micro-bubble injection. The local wall concentrations were increased with gas injection by more than an order of magnitude in many cases. These results show that synergistic drag reduction occurs with combined injection as a result of increased polymer wall concentrations.
Grid Requirements for Multiscale Resolution in Separated Unsteady High Speed Turbulent Flows
Authors: Basu D. , Hamed A. , Das K.
Published: September 2008

This study deals with the computational grid requirements in multiscale simulations of separated turbulent flows at high Reynolds number. The two-equation k-ε based DES (Detached Eddy Simulation) model is implemented in a full 3-D Navier-Stokes solver and numerical results are presented for transonic flow solution over an open cavity. Results for the vorticity, pressure fluctuations, SPL (Sound Pressure level) spectra and for modeled and resolved TKE (Turbulent Kinetic Energy) are presented and compared with available experimental data and with LES results. The results indicate that grid resolution significantly influences the resolved scales and the peak amplitude of the unsteady sound pressure level (SPL) and turbulent kinetic energy spectra.
Effect of Injection Parameters on the Spray Characteristics of DME Fuel
Authors: Ryu Bong Woo , Bang Seung Hwan , Suh Hyun Kyu , Lee Chang Sik
Published: September 2008

The purpose of this study is to investigate the effect of injection parameters on the injection and spray characteristics of dimethyl ether and diesel fuel. In order to analyze the injection and spray characteristics of dimethyl ether and diesel fuel with employing high-pressure common-rail injection system, the injection characteristics such as injection delay, injection duration, and injection rate, spray cone angle and spray tip penetration was investigated by using the injection rate measuring system and the spray visualization system. In this work, the experiments of injection rate and spray visualization are performed at various injection parameters. It was found that injection quantity was decreased with the increase of injection pressure at the same energizing duration and injection pressure In the case of injection characteristics, dimethyl ether showed shorter of injection delay, longer injection duration and lower injected mass flow rate than diesel fuel in accordance with various energizing durations and injection pressures. Also, spray development of dimethyl ether had larger spray cone angle than that of diesel fuel at various injection pressures. Spray tip penetration was almost same development and tendency regardless of injection angles.
An Advanced Reciprocating Internal Combustion Engine Without Crankshaft and Connecting Rod Mechanisms
Authors: Fijalkowski Bogdan T.
Published: September 2008

An advanced reciprocating internal combustion engine without a crankshaft and connecting rod mechanisms that the author would like to present is based on another law of physics. The invention titled ‘Nano-Magneto-Rheological Mechatronic Commutator Internal Combustion Engine’, that is concisely termed the Fijalkowski engine by someone, is based on a whole new propulsion engineering solution that has no analogies in the world. Thus, this paper focuses on an advanced reciprocating internal combustion engine termed the Fijalkowski engine, which may utilize a nano-magneto-rheological mechatronic commutator that may replace the crankshaft and connecting rod (conrod) mechanisms. This mechatronic commutator may let nano-magneto-rheological rotary ratchets oscillate in a controlled wobble while keeping the output shaft spinning smoothly; and although opposed pistons and opposed cylinders similar to those in automotive ‘boxer’ engines may power the Fijalkowski engine, it may also utilize opposed cylinders containing four pairs of two end-to-end opposed pistons for higher power densities. The nano-magneto-rheological mechatronic commutator may be utilized to convert between one form of mechanical motion that is linear, reciprocating motion of pistons and another — that is rotary motion of the output shaft.
Comparison of Three Types of Common Rail Systems Suited for Diesel Engines From 1 to 5 Megawatt
Authors: Ganser Marco , Moser Ulrich
Published: September 2008

The basic physical law governing the injection in Common Rail Systems is the compressibility of the fuel. The effects of pressure wave dynamics, the layout of the system volume and its geometrical distribution strongly affect the injection events at every injector. In this Paper, three different arrangements of system volumes and their effect upon the performance of the individual injectors are compared using the hydraulics simulation tool AMESim. Two systems are known in the passenger car and the heavy duty diesel engine domains. The third system is new and takes advantage of pressure wave dynamics to tailor the injection event. This system is best suited for Diesel Engines with a power from 1 to 5 MW, as used in locomotives, ships, power generation and heavy earthmoving machinery. It produces a more favorable pattern of the injection pressure and injection rate shape during any injection event by hydraulically interconnecting the individual injector’s accumulators during the injection and taking advantage of pressure wave dynamics. Right after the end of each injection, dynamic pressure pulsations are evened out with a dampening device. A multi-cylinder system provides equal conditions for all injections. Its very simple design and increased performance makes the novel system of very attractive use in the above mentioned fields.
Effects of Lubricant Viscosity on Ring/Liner Friction in Advanced Reciprocating Engine Systems
Authors: Takata Rosalind , Wong Victor W.
Published: September 2008

The piston ring-pack contributes a large portion of the mechanical losses in an internal combustion engine. In this study, the effects of lubricant viscosity are evaluated with the goal of reducing these mechanical losses. Oil viscosity affects friction directly in the hydrodynamic regime, where hydrodynamic friction increases with viscosity. It also influences boundary friction indirectly via oil film thickness — higher viscosity causes oil films to be thicker, which reduces asperity contact. At the optimum viscosity (the viscosity at which minimum friction losses are incurred) there is a balance between these hydrodynamic and boundary effects. As piston speed, ring loading, and other parameters change during the engine cycle, the optimum oil viscosity also changes. If the variation of viscosity could be controlled during the cycle, it could be maintained at an optimum at all times. In this study, several theoretical and realistic cases were studied to quantify the friction benefit that could be obtained if this were possible. Idealized cases with low viscosity near mid-stroke (to reduce hydrodynamic friction) and high viscosity near end-strokes (to reduce boundary contact) were considered, as were several more realistic cases based on temperature and shear-rate dependencies. It was found that, for the oil control ring studied, the effect on friction of keeping viscosity high near end-strokes is very small, and does not provide a substantial benefit (in terms of friction) over allowing viscosity to vary naturally with temperature and shear rate. Two mechanisms lead to the relatively small size of the friction benefit: the contribution to total cycle ring friction from the dead-center area is small, because of low piston speeds there; and any reduction in asperity contact due to increased viscosity is accompanied by an increase in hydrodynamic friction, which cancels out some of the benefit. Oil viscosity near mid-stroke, where most of the ring/liner friction is generated, is the dominant viscosity that controls the overall friction losses for the ring. Although its contribution to friction reduction is not large, maintaining high lubricant viscosity near dead-centers can lead to a reduction in wear in that region, because asperity contact decreases. For the ring-pack studied, a friction reduction of ∼7% is predicted when viscosity is reduced in the mid-stroke region (based on OCR effects alone). If end-stroke viscosity is also kept high, the end-stroke regions, where current engines experience the most wear, will see a reduction in asperity contact (although there will still be a slight wear increase in the mid-stroke). An end-stroke wear reduction of up to 25% is predicted by the current model.
An Experimental Study of Spark Anemometry for In-Cylinder Velocity Measurements
Authors: Gardiner D. P. , Wang G. , Bardon M. F. , LaViolette M. , Allan W. D.
Published: September 2008

It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current waveforms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. Whereas earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the free stream gas velocity. A lower velocity threshold exists below which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the free stream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.
Characterization of Particle Size, Number, and Mass Emissions From a Diesel Powered Generator
Authors: Khalek Imad A.
Published: September 2008

Total (volatile plus solid) and solid particle size, number, and mass emitted from a 3.8 kW diesel powered generator were characterized using a Scanning Mobility Particle Sizer (SMPS) that measures the size distribution of particles, and a catalytic stripper that facilitates the measurement of solid particles. The engine was operated at a constant speed for six steady-state engine operations ranging from idle to rated power. The solid particle size distributions were mainly monomodal lognormal distributions in nature reflecting a typical soot agglomerate size distribution with a number mean diameter in the size range from 98 nm to 37 nm as the load decreases from high to low. At idle, M6, however, the solid particle distribution was bimodal in nature with a high number of solid nanoparticles in the sub-20 nm size range. It is likely that these solid particles nucleated later in the combustion process from metallic ash typically present in the lube oil. The total particle size distributions exhibited a bimodal structure only at light load, M5, engine operation, where a high number of volatile nanoparticles were observed. The rest of the operating conditions exhibited monomodal distributions although the nature of the particles was vastly different. For the medium load modes, M2, M3, and M4, the particles were mainly solid particles. For the rated power, M1, and idle, M6, modes of engine operation, significant number of volatile particles grew to a size nearing that of soot particles making the distribution monomodal, similar to that of a solid particle distribution. This shows that monomodal distributions are not necessarily solid particle but they can be strongly dominated with volatile particles if significant particle growth takes place like the case at M1, and M6. The total number and mass concentration were extremely high at engine rated power. The number concentration exceeded 1.2 billion particles per cubic centimeter and the mass exceeded 750 milligrams per cubic meter. The number concentration is more than five orders of magnitude higher than a typical ambient level concentration, and the mass concentration is more than four orders of magnitude higher. It is important to indicate, however, that if the engine power rating is lowered by 35 percent from its designated level, both particle mass and number emissions will be reduced by two orders of magnitude. By measuring total and solid particle size and number concentration of particles, one can calculate other metrics such as surface area and mass to provide detail information about particle emissions. Such information can serve as an important database where all metrics of particle emissions are captured.
Flow-Through Filter Technology for Heavy Duty Diesel Engines
Authors: Farafontov Pavel , Williams Shazam , Muter John
Published: September 2008

Reducing particulate emissions from diesel engines has become a major challenge for regions of Europe, Japan and the United States. Many mobile applications have been successfully addressed with passively regenerating wall flow filters. However stationary engines, locomotives and other large constant speed engines often require a different approach to particulate filtration. Flow-through filter technologies have merit for these applications due to their low maintenance requirements, tolerance to misfueling and suitability for engines with high specific PM emissions. When considering the application of a particulate filter to any diesel engine the means of regeneration, or combustion of the accumulated soot, is of critical importance. In the case of filters which are regenerated through the use of a catalytic coating the duty cycle of the engine, and characteristics of the exhaust gas itself dictate the potential success or failure of the system. In many cases interruption of operation, whether due to insufficient regeneration rates, or for scheduled service to remove accumulated ash, is relatively more difficult to accept for locomotive and non-mobile engine operations. Locomotives, power generators and the like often accumulate large number of service hours between scheduled maintenance events and perform tasks where interruption of service can have costly consequences. Details of an investigation into the suitability of a flow-through filter for heavy-duty constant speed engines are presented. Aspects of the design, including materials selection, catalyst coating and performance under various conditions are discussed. Results from CFD and micro-dilution tunnel particulate sampling of full-scale devices support the progressive refinement of the design.