Continuous InkJet (CIJ) printing is a common 2-Dimensional printing technique that creates jets of ink that breakup into drops as they are propelled towards a substrate to create a print. Inkjet printing has been used not only to print on paper, but to manufacture a variety of devices including OLEDs, solar cells and microfluidic devices. In many cases, the ‘ink’ consists of a polymer dissolved in a volatile solvent. As this ink is sprayed on to the substrate, the solvent evaporates, leaving the polymer behind as the print. The addition of the polymer alters the physics of the problem significantly enough that it varies greatly from jetting only a fluid with nothing dissolved in it. Polymers impart viscoelasticity to the solution, creating ink jets that are long-lived and difficult to break into droplets. In order to maintain the formation of drops in a repeatable, uniform fashion, a disturbance of known magnitude is imposed upon the jet. While jetting a liquid with no additives in it, this disturbance governed jet breakup leads to the formation of satellite drops, smaller drops of fluid in-between the main jet drops. Satellite drops are an undesirable occurrence in inkjet printing because of their unpredictable behavior and potential to affect the quality of the print. However, the addition of polymers to the liquid can control and potentially suppress the formation of these satellite drops, greatly improving the print quality. The elasticity of iv the polymer and its ability to influence the jet behavior and formation of satellite drops is highly dependent on multiple factors including the backbone rigidity, molecular weight and the concentration in which it is present in the fluid. Strongly viscoelastic effects have a marked effect on the jet and their presence can be quantified quite easily. However, some polymers show weak viscoelastic behavior while present in the ink fluids and may or may not affect the jetting process. The objective of this study is to examine such a class of polymeric fluids that are weakly viscoelastic in the context of inkjet printing and satellite drop formation. Firstly, the fluids are tested in an extensional rheology setup called Capillary Breakup Extensional Rheometry – Drop-on-Substrate (CaBER-DoS) to quantify their extensional properties. Then, they are tested in an emulated inkjet printing setup. The goal is to quantify the impact of the aforementioned factors on jetting and using satellite drop behavior as a guiding metric to understanding viscoelastic behavior in inkjet printing fluids.

A three-dimensional flow field produced by supersonic twin-jet impingement is studied using a large eddy simulation (LES). The numerical model consists of two parallel axisymmetric jets of diameter 𝐷*, 3𝐷* apart, issuing from a plane which is at a distance H*=4𝐷* above the ground. The jet diameter 𝐷*, mean velocity 𝑊ₒ*, mean density 𝜌ₒ* and mean temperature 𝑇ₒ* at the jet center in the exit plane are used as reference values. The Mach number and Reynolds number of the jets are M=1.5 and Re=550,000, respectively. This model is closely related to the experimental setup of Elavarasan <i>et al.</i>(Elavarasan <i>et al.</i>, 2000). The three-dimensional time-dependent compressible Navier-Stokes equations are solved using the method of lines. The convective terms are discretized using a fifth-order WENO scheme, whereas the viscous terms are discretized using a fourth-order central-differencing scheme. A low-storage five-stage fourth-order Runge-Kutta scheme is used to advance the solution in time. Code verification is achieved by comparison with flat-plate boundary-layer linear stability analysis, and computational data by Bendiks <i>et al.</i> (Bendiks <i>et al.</i>, 1999). for a compressible turbulent round jet. Instantaneous flow, mean flow and Reynolds stresses for the twin-jet impingement are presented and discussed. The results reveal the existence of flapping behavior in the fountain. The flapping fountain is the vortical structure formed by the alternating merging of a primary vortex tube with a secondary vortex tube induced by the neighboring primary vortex tube. The nondimensional period of flapping is found to be 7𝐷*/𝑊ₒ*. High unsteadiness and strong interaction between the fountain and the jets are also observed. Due to the high diffusion and spreading rate of the fountain, the interaction between the fountain and the jets is only significant up to a height which is less than 3𝐷*. It is found that the mean peak velocity in the fountain is 0.40406 𝑊ₒ* and it occurs at 0.536607𝐷* from the ground. The suitability of the fifth-order WENO scheme to simulate turbulent flow field with embedded shocks is also demonstrated by its capability to capture unsteady shock waves in the impingement regions. / Ph. D.

Several flow control schemes were designed and tested to determine the most suitable method for reducing the momentum deficit in a rotor wake and thus attenuate rotor-stator interaction noise. A secondary concern of the project was to reduce the amount of blowing required air for wake filling and thus limit the efficiency penalty in an aircraft engine environment. Testing was performed in a linear blow down cascade wind tunnel, which produced an inlet Mach number of 0.345. The cascade consisted of five blades with the stagger angle, pitch, and airfoil cross-section representative of 90% span of the rotor geometry for NASA's Active Noise Control Fan (ANCF) test rig. The Reynolds number for the tests was based on inlet conditions and a chord length of 4 inches. Trailing edge jets, trailing edge slots, ejector pumps, and pressure/suction side jets were among the configurations tested for wake filling. A range of mass flow percentages were applied to each configuration and a pressure loss coefficient was determined for each. Considerable reduction in wake losses took place for discrete jet blowing techniques as well as pressure side and suction side jets. In the case of the pressure and suction side jets, near full wake filling occurred at 0.75% of the total mass flow. In terms of loss coefficients and calculated momentum coefficients, the suction/pressure surface jets were the most successful. Jets located upstream of the trailing edge helped to re-energize the momentum deficits in the wake region by using a flow pattern capable of mixing the region while also adding momentum to the wake. The slotted configuration was modeled after NASA's current blowing scheme and served as a baseline for comparison for all data. Digital particle image velocimetry was performed for flow visualizations as well as velocity analysis in the wake region. / Master of Science

The supersonic jet plumes that exhaust from the engines of tactical aircraft produce intense noise signatures that expose the Navy personnel working on the deck of aircraft carriers to dangerously high levels of noise that often results in hearing damage. Reducing the noise radiated by these supersonic plumes is of interest to the Department of Defense and is the primary motivation of this research. Fundamentally, jet noise reduction is achieved by manipulating the nozzle boundary condition to produce changes in the turbulence development and decrease the acoustic efficiency of coherent structures. The research presented here focuses on a novel jet noise reduction technique involving a centered thermal non-uniformity that alters the base flow by introducing a temperature-driven centerline velocity deficit into a perfectly expanded Mach 1.5 jet. The results indicate $2 pm 0.5$ dB reductions in peak narrowband spectral sound pressure levels upstream of peak directivity directions for the non-uniform jet compared to a thermally uniform baseline, even for static thrust matched conditions. This reduction is hypothesized to be related to perturbations induced by the thermal non-uniformity that convect inside the irrotational core and reduce the correlation length scales of turbulence at locations far downstream. This hypothesis was evaluated by studying the coherent turbulence via its convective hydrodynamic footprint in the near-field. An indirect investigation of the near-field using a far-field-informed model of the wavenumber-frequency spectra indicate a reduction in the energy contained in the tail of the wavenumber spectra amplitude, suggesting a reduction in the size of large scale structures. A direct evaluation of the spatio-temporal behavior of the near-field was performed using temporally resolved schlieren images. Space-time correlations of the frequency-filtered near-field identified high frequency acoustic waves radiated by compactly coherent turbulent structures and low frequency Mach waves produced by large scale instabilities. In the thermally non-uniform case these features and their sources were found to be decorrelated at downstream regions. These results provide strong evidence that a centered thermal non-uniformity reduces the radiated noise compared to a uniform baseline by shortening the correlation length scales of coherent structures in regions far from the nozzle exhaust. / Doctor of Philosophy / A more complete understanding of the intense noise sources present in supersonic jet plumes is of value to both government and industry, and is a necessary step towards optimizing noise reduction techniques. Tactical aircraft that operate on the deck of aircraft carriers expose Navy personnel to dangerously high levels of noise that often results in permanent hearing damage. Supersonic jet noise reduction is also of relevance to the recent efforts to revitalize supersonic air transport over land. For supersonic air transport to become a reality, the noise produced by these future aircraft during takeoff and landing must meet the increasingly stringent community noise requirements. Fundamental jet noise research is needed to guide the design of future engine architectures for these aircraft to ensure their commercial success. The research presented herein examines a novel noise reduction technique that involves a centered thermal non-uniformity consisting of a heated jet plume with a spot of locally cooler, slower moving air concentrated along the centerline of a Mach 1.5 jet. This temperature driven velocity deficit is shown to reduce the radiated noise by up to 2.5 dB at peak frequencies and at angles just outside of the peak directivity direction. The cause of the noise reduction is hypothesized be related to a reduction in the size of the coherent structures that radiate a majority of the noise produced by turbulent jets. This hypothesis is evaluated by examining the 'footprint' of the coherent structures in the ambient field directly outside of the jet shear layer in an area called the near-field. An indirect investigation of the near-field using a far-field informed analytic model suggests a reduction in the size of large scale structures. A direct evaluation of the space time structure of the near-field was performed using temporally resolved schlieren images. Statistical processing of the density gradient provided by the schlieren images revealed acoustically intense structures known as Mach waves and high frequency acoustic waves. These features and their sources, large scale instabilities and compactly coherent turbulence, were found to be decorrelated by the introduction of the thermal non-uniformity. These results provide strong evidence that the centered thermal non-uniformity produces a noise benefit by reducing the size of the turbulent structures.

This thesis is primarily about the mapping and analyze of the phenomenon of an impinging jet by experimental measurements and numerical simulations by CFD. The mapping shows the characteristics of velocity in and around the impinging jet with different conditions. Additional studies were made by analyzing the pressure along the vertical jet axis, but also weight measurements were part of the investigation. The measurements covered the range from 10 m/s, 20 m/s and 30 m/s, which corresponds to a Reynolds number of 17 000, 34 000 and 50 000. The impinging jet is therefore considered to be highly turbulent. The main difference from previous studies is the use of the ultrasonic anemometer to measure the velocities. These create the ability of measuring the velocities on three coordinates. The jet’s contour was crucial to determine the penetration of ambient air flowing into the jet with an angle of around 88° and the entrainment of the ambient air multiple the jet volume flow. In comparison with CFD, the number of cells in the mesh design and the type of model plays a substantial role. The model k-ε Realized came closest to the experimentally measurements, while the SST k-ω and RNG k-ε EWF had far more entrainment of the ambient air into the impinging jet. / Detta examensarbete handlar om att kartlägga och analysera fenomenet av en ”impinging jet” genom experimentella mätningar samt numeriska simuleringar som CFD. Undersökningen visar karakteristiken av hastigheten i och kring strålen med olika förutsättningar. Kompletterande undersökningar gjordes för trycket i luftstrålens centrum längs den vertikala axeln, men även viktmätningar var del av undersökningen. Mätningarna omfattade hastigheter från 10 m/s, 20 m/s och 30 m/s som motsvarar ett Reynoldstal med 17 000, 34 000 och 50 000. Luftstrålen betraktas därför som turbulent. Det som skiljer sig från tidigare experiment är att hastigheten mättes med en ultrasonic anemometer som egentligen används inom metrologin för att mäta vindhastigheter. Därmed skapades en tredimensionell bild av hastigheten i och kring luftstrålen. Mätområdet sträckte sig från strålens utgångspunkt ner till strax ovanför plattan. Luftstrålens fastställda kontur var avgörande för att bestämma den inträngande omgivningsluften som strömmar in i strålen med en genomsnittlig vinkel av 88°. Denna inströmmande omgivningsluft flerfaldigade strålens volym. I jämförelse med CFD simuleringen visades att antal celler i meshen är avgörande för att skapa liknande och reala förutsättningar. Vid undersökningen av den inträngande omgivningsluften visades även att själva modellen spelar en avgörande roll. Det var modellen k-ε Realized som kom närmast mätningarna. Däremot uppvisade SST k-ω och RNG k-ε EWF modellerna mycket mer inträngande omgivningsluft i jämförelse med mätningarnas resultat.

Supersymmetry (SUSY) is the most motivated scenario beyond the Standard Model (SM) addressing the problems of the SM in an elegant way by establishing a symmetry which relates matter particles to interaction particles and vice versa. The simplest phenomenologically viable supersymmetric theory is the Minimal Supersymmetric Standard Model (MSSM) which can be accommodated to minimal Supergravity (mSuGra) theory in order to both take gravity into account and constrain its parameter space. CMS detector is one of the general purpose detectors constructed at LHC (Large Hadron Collider) which targets to search for SUSY signal. This thesis presents a search strategy for SUSY in three different fully hadronic jet topologies with the CMS detector. Di-jet, 3-jet, and 4-jet event topologies offer clear signatures for SUSY searches and the key SUSY decay modes of these jet topologies appear to be squark pair production, squark-gluino production, and gluino pair production, respectively. In these jet topologies, an important kinematical variable named alpha, &amp / #945 / is used to separate SUSY signal test points from the SM background events including QCD, EWK (Electroweak), and invisible decay of Z boson processes. Alpha variables are found to be very useful in terms of enhancing SUSY signal while rejecting all QCD events. Discriminating power of alpha variables are shown in terms of signal-to-background and signal significance calculations and the results are found to be promising which further encourage searches for SUSY signal in jet event topologies with the early CMS data at 1 f b^{&amp / #8722 / 1} integrated luminosity.

Au cours de ces dernières années les activités de recherches sur les carburants reformulés destinés au secteur aéronautique ont considérablement augmenté. En effet, le fort développement du secteur aérien pousse les scientifiques à chercher une alternative au carburéacteur destiné aux aérodynes dans le but d’économiser le pétrole mais aussi de lutter contre le réchauffement climatique et la pollution atmosphérique. Dans cette thèse nous avons mené des expériences d’oxydation sur trois hydrocarbures lourds, un kérosène conventionnel Jet A-1, des kérosènes reformulés (bio kérosène) et de synthèse (carburant issu de la synthèse Fischer-Tropsch). Ces études ont été réalisées en réacteur auto-agité par jets gazeux à haute pression (10 atm), dans un large domaine de températures (550-1150 K) et à trois richesses (Ф=0,5, 1 et 2). Les analyses par spectrométrie d’absorption infrarouge à transformée de Fourier (IRTF) et la chromatographie en phase gazeuse (CPG-FID-TCD-MS) nous ont permis de mesurer les profils de concentration des réactifs, des produits finals et des intermédiaires stables en fonction de la température. Des mécanismes cinétiques détaillés adaptés aux composés étudiés ont été développés et validés par confrontation avec les résultats expérimentaux. / In recent years research activities on reformulated fuels for the aviation industry have increased. Indeed, the strong development of the airline industry pushes scientists to seek for alternative jet fuel intended for aerodynes in order to preserve oil but also to fight against global warming and air pollution. In this thesis we have conducted experiments on the oxidation of three heavy hydrocarbons, a conventional Jet A-1, reformulated jet fuels (bio-kerosene) and synthetic kerosene (Fischer-Tropsch jet fuel). These studies were carried out in jet stirred reactor at high pressure (10 atm), in a wide temperature range (550-1150 K), for three equivalence ratios (Ф=0.5, 1, and 2). Chemical analyses by Fourier Transformed Infra-Red spectrometry (FTIR) and gas chromatography (GC-FID-TCD-MS) allowed us to measure concentration profiles of reactants, stable intermediates and final products versus temperature. Detailed chemical kinetic reaction mechanisms adapted to the studied compounds were developed and validated by comparison with experimental results.

The work developed in the master's program, describes the technology of water jet cutting. The theoretical part deals with the description of this technology and it explains the basic concepts used in this field. The practical part was designed to verify some theoretical knowledge. Therefore, several experiments were performed, while there was studied the influence of abrasives on the final quality of the surface and the level of the generated noise. The practical part was completed by the production of the selected component and its technical and economic evaluation.

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