Slot Film Cooling: A Comprehensive Experimental Characterization

When components of a propulsion system are exposed to elevated flow temperatures there is a risk for catastrophic failure if the components are not properly protected from the thermal loads. Among several strategies, slot film cooling is one of the most commonly used, yet poorly understood active cooling techniques. Tangential injection of a relatively cool fluid layer protects the surface(s) in question, but the turbulent mixing between the hot mainstream and cooler film along with the presence of the wall presents an inherently complex problem where kinematics, thermal transport and multimodal heat transfer are coupled. Furthermore, new propulsion designs rely heavily on CFD analysis to verify their viability. These CFD models require validation of their results, and the current literature does not provide a comprehensive data set for film cooling that meets all the demands for proper validation, namely a comprehensive (kinematic, thermal and boundary condition data) data set obtained over a wide range of conditions. This body of work aims at solving the fundamental issue of validation by providing high quality comprehensive film cooling data (kinematics, thermal mixing, heat transfer). 3 distinct velocity ratios (VR=uc/u∞) are examined corresponding to wall-wake (VR~0.5), min-shear (VR ~ 1.0), and wall-jet (VR~2.0) type flows at injection, while the temperature ratio TR= T∞/Tc is approximately 1.5 for all cases. Turbulence intensities at injection are 2-4% for the mainstream (urms/u∞, vrms/u∞,), and on the order of 8-10% for the coolant (urms/uc, vrms/uc,). A special emphasis is placed on inlet characterization, since inlet data in the literature is often incomplete or is of relatively low quality for CFD development. The data reveals that min-shear injection provides the best performance, followed by the wall-jet. The wall-wake case is comparably poor in performance. The comprehensive data suggests that this relative performance is due to the mixing strength of each case, as well as the location of regions of strong mixing with respect to the wall. Kinematic and thermal data show that strong mixing occurs in the wall-jet away from the wall (y/s>1), while strong mixing in the wall-wake occurs much closer to the wall (y/s<1). Min-shear cases exhibit noticeably weaker mixing confined to about y/s=1. Additionally to these general observations, the experimental data obtained in this work is analyzed to reveal scaling laws for the inlets, near-wall scaling, detecting and characterizing coherent structures in the flow as well as to provide data reduction strategies for comparison to CFD models (RANS and LES).

Instrumentation studies for plasma jet and hypersonic wind tunnel,

"This research was supported by the McDonnell Aircraft Corporation under Contract no. 6140-20 P.O. 7S4899-R."

Approximate solutions to optimum flight trajectories for a turbo-jet powered aircraft,

"Purdue Research Foundation. Research project no. 1255. Project Ae-25. This research was supported by the National Advisory Committee for Aeronautics, Washington, D. C., under Contract no. NAW-6465."

Les armes de jet d’Argilos : catalogue typologique

Quelques sites archéologiques comme Olympie, Stymphalos et Olynthe possèdent respectivement un répertoire faisant l’étude des armes de jet retrouvées durant une série de campagnes de fouilles archéologiques. Parmi ces indexes, figurent fréquemment des pointes de flèche, des balles de fronde et des saurotères (contrepoids de lance ou de javelot) provenant de différentes périodes historiques gréco-romaines. À travers les 20e et 21e siècle de notre ère, des spécialistes comme D. Robinson (1931), A. Snodgrass (1964), H. Baitinger (2001), C. Hagerman (2014) dédièrent une partie de leur expertise pour produire des synthèses sur ces objets jadis négligés. Ainsi, ils parvinrent à créer de grandes encyclopédies commentées composées de projectiles retrouvés en sol grec. À l’aide de ces bases de données, les archéologues militaires sont en mesure d’établir des datations et l’origine prétendue de certains types de projectiles. Jusqu’en 2015, les artéfacts militaires trouvés sur le site archéologique d’Argilos n’avaient jamais fait l’objet d’une étude de synthèse. D’abord, inspiré par de publications semblables, ces projectiles furent soumis à un inventaire sous forme de catalogue. Au total, deux types de balles de fronde en plomb, onze types de pointes de flèche et un type de saurotère furent identifiés. Finalement, ce nouveau contenu fut assujetti à des analyses comparatives avec d’autres sites archéologiques possédant des données similaires. Les conclusions découlant de ces analogies donnèrent naissance à la première typologie des armes de jet argilienne. Certes, les analyses se heurtèrent à certains obstacles, notamment à une compréhension de la quasi-inexistence d'une pointe de flèche typiquement "grecque" et à la confusion systématique quant à la distinction entre un saurotère et une pointe de javelot, voire possiblement un carreau de gastraphétès (une sorte d’arbalète imposante utilisée lors de sièges durant le 4e siècle av. J.-C.). En partie, ceci découle de l'historique d'échanges entre la Grèce et les autres peuples méditerranéens, balkaniques et orientaux. En outre, de nombreuses réformes militaires des périodes archaïque et classique provoquèrent une évolution constante sur les aspects stratégiques et les tactiques militaires. Considérant ces facteurs parmi tant d'autres et le fait qu'Argilos ait été une fondation grecque en territoire thraco-macédonien, la possibilité d'influence "étrangère" devient alors prépondérante sur la typologie des projectiles argiliens publiée dans le présent mémoire. Avec beaucoup d’espoir, nous croyons sans équivoque que ce travail de recherche contribuera grandement non seulement à l’histoire d’Argilos, mais aussi à l’étude des projectiles en Grèce du nord.

Comportamento ao desgaste erosivo de um aço inoxidável utilizado em hélice de moto aquática

Dissertação (mestrado)—Universidade de Brasília, Faculdade UnB Gama, Programa de Pós-graduação em Integridade de Materiais da Engenharia, 2015.

Numerical prediction of thermal and dynamic characteristics of a fireinduced ceiling-jet

The aim of this thesis is to test the ability of some correlative models such as Alpert correlations on 1972 and re-examined on 2011, the investigation of Heskestad and Delichatsios in 1978, the correlations produced by Cooper in 1982, to define both dynamic and thermal characteristics of a fire induced ceiling-jet flow. The flow occurs when the fire plume impinges the ceiling and develops in the radial direction of the fire axis. Both temperature and velocity predictions are decisive for sprinklers positioning, fire alarms positions, detectors (heat, smoke) positions and activation times and back-layering predictions. These correlative models will be compared with a 3D numerical simulation software CFAST. For the results comparison of temperature and velocity near the ceiling. These results are also compared with a Computational Fluid Dynamics (CFD) analysis, using ANSYS FLUENT.

Translation Studies on an Annular Field Reversed Configuration Device for Space Propulsion

This research investigated annular field reversed configuration (AFRC)devices for high power electric propulsion by demonstrating the acceleration of these plasmoids using an experimental prototype and measuring the plasmoid's velocity, impulse, and energy efficiency. The AFRC plasmoid translation experiment was design and constructed with the aid of a dynamic circuit model. Two versions of the experiment were built, using underdamped RLC circuits at 10 kHz and 20 kHz. Input energies were varied from 100 J/pulse to 1000 J/pulse for the 10 kHz bank and 100 J/pulse for the 20 kHz bank. The plasmoids were formed in static gas fill of argon, from 1 mTorr to 50 mTorr. The translation of the plasmoid was accomplished by incorporating a small taper into the outer coil, with a half angle of 2°. Magnetic field diagnostics, plasma probes, and single-frame imaging were used to measure the plasmoid's velocity and to diagnose plasmoid behavior. Full details of the device design, construction, and diagnostics are provided in this dissertation. The results from the experiment demonstrated that a repeatable AFRC plasmoid was produced between the coils, yet failed to translate for all tested conditions. The data revealed the plasmoid was limited in lifetime to only a few (4-10) μs, too short for translation at low energy. A global stability study showed that the plasma suffered a radial collapse onto the inner wall early in its lifecycle. The radial collapse was traced to a magnetic pressure imbalance. A correction made to the circuit was successful in restoring an equilibrium pressure balance and prolonging radial stability by an additional 2.5 μs. The equilibrium state was sufficient to confirm that the plasmoid current in an AFRC reaches a steady-state prior to the peak of the coil currents. This implies that the plasmoid will always be driven to the inner wall, unless it translates from the coils prior to peak coil currents. However, ejection of the plasmoid before the peak coil currents results in severe efficiency losses. These results demonstrate the difficulty in designing an AFRC experiment for translation as balancing the different requirements for stability, balance, and efficient translation can have competing consequences.

Conversion of a Micro, Glow-Ignition, Two-Stroke Engine from Nitromethane-Methanol Blend Fuel to Military Jet Propellant (JP-8)

The goal of the thesis "Conversion of a Micro, Glow-Ignition, Two-Stroke Engine from Nitromethane-Methanol Blend Fuel to Military Jet Propellant (JP-8)" was to demonstrate the ability to operate a small engine on JP-8 and was completed in two phases. The first phase included choosing, developing a test stand for, and baseline testing a nitromethane-methanol-fueled engine. The chosen engine was an 11.5 cc, glow-ignition, two-stroke engine designed for remote-controlled helicopters. A micro engine test stand was developed to load and motor the engine. Instrumentation specific to the low flow rates and high speeds of the micro engine was developed and used to document engine behavior. The second phase included converting the engine to operate on JP-8, completing JP-8-fueled steady-state testing, and comparing the performance of the JP-8-fueled engine to the nitromethane-methanol-fueled engine. The conversion was accomplished through a novel crankcase heating method; by heating the crankcase for an extended period of time, a flammable fuel-air mixture was generated in the crankcase scavenged engine, which greatly improved starting times. To aid in starting and steady-state operation, yttrium-zirconia impregnated resin (i.e. ceramic coating) was applied to the combustion surfaces. This also improved the starting times of the JP-8-fueled engine and ultimately allowed for a 34-second starting time. Finally, the steady-state data from both the nitromethane-methanol and JP-8-fueled micro engine were compared. The JP-8-fueled engine showed signs of increased engine friction while having higher indicated fuel conversion efficiency and a higher overall system efficiency. The minimal ability of JP-8 to cool the engine via evaporative effects, however, created the necessity of increased cooling air flow. The conclusion reached was that JP-8-fueled micro engines could be viable in application, but not without additional research being conducted on combustion phenomenon and cooling requirements.

Deposition of thin films by a non-equilibrium atmospheric pressure Plasma Jet: a poly-diagnostic study

The use of atmospheric pressure plasmas for thin film deposition on thermo-sensitive materials is currently one of the main challenges of the plasma scientific community. Despite the growing interest in this field, the existing knowledge gap between gas-phase reaction mechanisms and thin film properties is still one of the most important barriers to overcome for a complete understanding of the process. In this work, thin films surface characterization techniques, combined with passive and active gas-phase diagnostic methods, were used to provide a comprehensive study of the Ar/TEOS deposition process assisted by an atmospheric pressure plasma jet. SiO2-based thin films exhibiting a well-defined chemistry, a good morphological structure and high uniformity were studied in detail by FTIR, XPS, AFM and SEM analysis. Furthermore, non-intrusive spectroscopy techniques (OES, filter imaging) and laser spectroscopic methods (Rayleigh scattering, LIF and TALIF) were employed to shed light on the complexity of gas-phase mechanisms involved in the deposition process and discuss the influence of TEOS admixture on gas temperature, electron density and spatial-temporal behaviours of active species. The poly-diagnostic approach proposed in this work opens interesting perspectives both in terms of process control and optimization of thin film performances.

Optimization and development of low environmental impact propulsion systems

The aim of the Ph.D. research project was to explore Dual Fuel combustion and hybridization. Natural gas-diesel Dual Fuel combustion was experimentally investigated on a 4-Stroke, 2.8 L, turbocharged, light-duty Diesel engine, considering four operating points in the range between low to medium-high loads at 3000 rpm. Then, a numerical analysis was carried out using a customized version of the KIVA-3V code, in order to optimize the diesel injection strategy of the highest investigated load. A second KIVA-3V model was used to analyse the interchangeability between natural gas and biogas on an intermediate operating point. Since natural gas-diesel Dual Fuel combustion suffers from poor combustion efficiency at low loads, the effects of hydrogen enriched natural gas on Dual Fuel combustion were investigated using a validated Ansys Forte model, followed by an optimization of the diesel injection strategy and a sensitivity analysis to the swirl ratio, on the lowest investigated load. Since one of the main issues of Low Temperature Combustion engines is the low power density, 2-Stroke engines, thanks to the double frequency compared to 4-Stroke engines, may be more suitable to operate in Dual Fuel mode. Therefore, the application of gasoline-diesel Dual Fuel combustion to a modern 2-Stroke Diesel engine was analysed, starting from the investigation of gasoline injection and mixture formation. As far as hybridization is concerned, a MATLAB-Simulink model was built to compare a conventional (combustion) and a parallel-hybrid powertrain applied to a Formula SAE race car.

Cross-population radio galaxies as a test of the jet-accretion relationship

Radio galaxies (RGs) are extremely relevant in addressing important unknowns concerning the interaction among black hole accretion, radio jets, and the environment. In the classical scheme, their accretion rate and ejection of relativistic jets are directly linked: efficient accretion (HERG) is associated with powerful edge-brightened jets (FRIIs); inefficient accretion (LERG) is associated with weak edge-darkened jets (FRIs). The observation of RGs with an inefficient engine associated with edge-brightened radio emission (FRII-LERGs) broke this scheme. FRII-LERGs constitute a suitable population to explore how accretion and ejection are linked and evaluate the environment's role in shaping jets. To this aim, we performed a multiwavelength study of different RGs catalogs spanning from Jy to mJy flux densities. At first, we investigated the X-ray properties of a sample of 51 FRIIs belonging to the 3CR catalog at z<0.3. Two hypotheses were invoked to explain FRII-LERGs behavior: evolution from classical FRIIs; the role of the environment. Next, we explored the mJy sky by studying the optical-radio properties of hundreds of RGs at z<0.15 (Best & Heckman 2012 sample). FRII-LERGs appear more similar to the old FRI-LERGs than to the young FRII-HERGs. These results point towards an evolutive scenario, however, nuclear time scale changes, star population aging, and kpc-Mpc radio structure modification do not agree. The role of the Mpc environment was then investigated. The Wen et al. 2015 galaxy clusters sample, built exploiting the SDSS survey, allowed us to explore the habitat of 7219 RGs at z<0.3. Most RGs are found to live in outside clusters. For these sources, differences among RG classes are still present. Thus, the environment is not the key parameter, and the possibility of intrinsic differences was reconsidered: we speculated that different black hole properties (spin and magnetic field at its horizon) could determine the observed spread in jet luminosity.

Experimental characterization of a planar jet by hot-wire anemometry

The study of turbulence is also nowadays a problem that does not have solution from the mathematical point of view due to the lack of solution to link the mean part of the flow with the fluctuating one. To solve this problem, in the CICLoPE laboratory of Predappio, experiments on different type of jets are performed in order to derive a closure model able to close our mathematical model. One of the most interesting type of jet that could be studied is the planar turbulent free jet which is a two dimensional canonical jet characterized by the self-similarity condition of the velocity profiles. To study this particular jet, a new facility was built. The aim of this project is to characterize the jet at different distances from the nozzle exit, for different values of Reynolds number, to demonstrate that the self-similarity condition is respected. To do that, the evaluation of quantities such as spreading rate, centerline velocity decay and relation between fluctuations and mean part of the flow has to be obtain. All these parameters could be detected thanks to the use of single and X hot-wire anemometry with which it is possible to analyzed the fluctuating behaviour of the flow by associating to an electric signal a physical variable expressed in terms of velocity. To justify the data obtain by the measures, a comparison with results coming from the literature has to be shown.

Development and Automatization of a Planar Jet Wind Tunnel for the X-wire Calibration

The scope of this study is to design an automatic control system and create an automatic x-wire calibrator for a facility named Plane Air Tunnel; whose exit creates planar jet flow. The controlling power state as well as automatic speed adjustment of the inverter has been achieved. Thus, the wind tunnel can be run with respect to any desired speed and the x-wire can automatically be calibrated at that speed. To achieve that, VI programming using the LabView environment was learned, to acquire the pressure and temperature, and to calculate the velocity based on the acquisition data thanks to a pitot-static tube. Furthermore, communication with the inverter to give the commands for power on/off and speed control was also done using the LabView VI coding environment. The connection of the computer to the inverter was achieved by the proper cabling using DAQmx Analog/Digital (A/D) input/output (I/O). Moreover, the pressure profile along the streamwise direction of the plane air tunnel was studied. Pressure tappings and a multichannel pressure scanner were used to acquire the pressure values at different locations. Thanks to that, the aerodynamic efficiency of the contraction ratio was observed, and the pressure behavior was related to the velocity at the exit section. Furthermore, the control of the speed was accomplished by implementing a closed-loop PI controller on the LabView environment with and without using a pitot-static tube thanks to the pressure behavior information. The responses of the two controllers were analyzed and commented on by giving suggestions. In addition, hot wire experiments were performed to calibrate automatically and investigate the velocity profile of a turbulent planar jet. To be able to analyze the results, the physics of turbulent planar jet flow was studied. The fundamental terms, the methods used in the derivation of the equations, velocity profile, shear stress behavior, and the effect of vorticity were reviewed.

Respostas agudas de parâmetros biomecânicos à utilização de diferentes tamanhos de palmar no nado crawl

Universidade Estadual de Campinas . Faculdade de Educação Física

O campo atrativo perceptual do nadar (CAPn) e a propulsão na natação

Universidade Estadual de Campinas . Faculdade de Educação Física