<p>This research focuses on experiments on compression-induced shock wave/boundary-layer interactions conducted in the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) at Purdue University. The BAM6QT facilitates a low-freestream-noise hypersonic test environment more similar to that experienced in flight than a conventional wind tunnel. Measurements were captured on two sliced 7° half-angle cones with finite-span compression ramps. On the first, the slice was cut parallel to the axis of the cone to build upon previous measurements in hypersonic flow. While similar geometries have been analyzed for over 30 years in experiment and computation, there are significant gaps in understanding of the underlying mechanisms leading to instability and transition on the ramp. Further, in low-noise Mach 6 flow, the boundary layer separated at the leading edge of the slice, which is unlikely to occur on a real flight vehicle. Thus, on the second model, the slice was cut at a 4° incline to the</p> <p>cone axis to facilitate the growth of an attached laminar boundary layer on the slice. Using this configuration, the ramp-induced boundary-layer thickening initiated between the slice leading edge and the ramp leading edge, allowing the investigation of a ‘naturally’ formed separated region. </p> <p><br></p> <p>Data were captured at angles of attack ranging from 0° to 6°, on compression ramp angles ranging from 10° to 20°, and for freestream Reynolds numbers of 2.5×10^6/m to 12×10^6/m. To analyze the mean-flow behavior of the separation bubble as it changes with the above parametrics, time-averaged schlieren visualization was used to provide off-surface visualization of the flowfield, allowing estimates of reattachment position and separation bubble size. In all cases, reattachment position was shown to move upstream with an increase in angle of attack, an increase in ramp angle, and an increase in Reynolds number. However, on the model with the inclined slice, the Reynolds number impacted reattachment location to a much lesser extent. </p> <p><br></p> <p>Heat transfer measurements on the ramp revealed regions with the most significant aerothermal loading. Streamwise streaks of high heating originating at the ramp edges and centerline were observed to increase in magnitude with an increase in Reynolds number, angle of attack, and ramp angle. On the model with the inclined slice, many streaks of high heating were observed that increased in quantity and magnitude with angle of attack and ramp angle. Root mean squared pressure fluctuations computed from surface pressure measurements were shown to follow similar trends to centerline heat transfer results for both models. Angle of attack, ramp angle, and slice angle are shown to play a dominant role in transition. Finally, the importance of quiet tunnels is made remarkably clear, as the BAM6QT operating in its conventional-noise configuration resulted in drastically different results.</p> <p><br></p> <p>For measurement of shock wave/boundary-layer instabilities, schlieren frames were captured at 100,000 fps to allow measurement of low-to-mid-frequency fluctuations of the recirculation zone edge. Shear layer flapping frequencies were found to occur at around 1100–1200 Hz, which increased with angle of attack to up to 1600 Hz. It is likely that this is an inherent instability in the separation bubble itself, rather than a function of freestream disturbances, and may be indicative of an ‘expansion and relaxation’ effect known as bubble breathing. Additional measurements using low-frequency-capable pressure sensors must be captured to determine whether this breathing effect manifests on the model slice or ramp. </p>

Internal waves are generated in stratified fluids, like the ocean, where density increases with depth. Tides are one of the major generation mechanisms of internal waves. As the tides move water back and forth over underwater topography, internal waves can be generated. Topography slope and amplitude are major factors in the behavior of the generated internal wave field. In order to further understand the effects topographic shape plays, the effect of asymmetry on internal waves is investigated. This research investigates internal waves generated by dual-ridge topographies. Four cases of symmetric topographies, T, M, W, and W2, with three different peak spacings are compared to their singular ridge counter parts at three oscillation frequencies, ω = 0.6N, ω = 0.75N, and ω = 0.9N. Both subcritical and supercritical symmetric ridges were investigated. Experiments were also performed for subcritical, asymmetric dual ridges at the middle oscillation frequency. The internal wave fields were captured with synthetic schlieren and analyzed with the Hilbert transform and sum of kinetic energy in wavenumber space. It is found that for wave fields from substantially separated ridges, mixing and wave interference occurs that decreases total kinetic energy of the system.

<p dir="ltr">Examination of gaseous detonation flow-fields represents a unique experimental challenge. High-speed shock interaction within a reactive mixture manifests combustion modes across a range of spatial-temporal scales. While the kinetics along the leading front are often characterized by adiabatic compression, simultaneously strong shear induces turbulent mixing in downstream portions of the flow. This all occurs within a wave structure typically traveling near 2000 m/s. To advance fundamental understanding, high-resolution diagnostics are required to make quantitative, time-resolved measurements of the unsteady detonation propagation.</p><p dir="ltr">In this work, detonations are experimentally studied in a single-shot, narrow channel using non-intrusive optical diagnostics. The change in wave structure between mixtures fueled by methane and natural gas was characterized using 175 kHz schlieren and CH* chemiluminescence imaging. The effect of the higher order alkanes in natural gas is speed up the reaction kinetics and produce a wave structure with smaller spatial scales and in which reaction occurs closer to the leading shock front.</p><p dir="ltr">A schlieren system operating at a rate of 5 MHz is then implemented to resolve the spatial-temporal oscillation of the leading shock front. These images are used to compute the lead shock normal speed, which enables a statistical analysis of the oscillating shock velocity. The moments of distribution are compared with computed instability levels of sixteen mixtures and a positive correlation is found. Simultaneous chemiluminescence is used to create joint distribution of shock speed and chemical length scale, which are then compared with the quasi-steady reaction zone solution.</p><p dir="ltr">Experiments are performed with highly nitrogen diluted mixtures of methane and oxygen to examine specific flow features. Different regimes of transverse wave reactivity are observed, from nonreactive to detonative. The transverse detonation wave structure is modeled using oblique shock relations and good agreement is found. The chemical length scales within the configuration are compared to the relevant expansion scales to explain the observed near-steady propagation. Distinct reactive processes following transverse wave collision are also captured. In one instance an explosion immediately occurs, while in the other a reactive gas jet grows from the point of collision. An unsteady reaction zone model is applied to understand the reaction mode within the jet.</p><p dir="ltr">Lastly, 300 kHz OH PLIF is performed to study small scale and weak reaction structures within the flow. The evolution of deflagrative burning mechanisms becomes resolvable using this technique, which highlights the benefit of its use.</p>

[ES] En los últimos años, la evolución de las tecnologías de inyección ha permitido no solo mejorar el proceso de mezcla, sino también controlar con precisión los parámetros de inyección, agregando flexibilidad a los sistemas para nuevas estrategias y un grado adicional de complejidad para los investigadores. Más aún, las estrategias de inyecciones múltiples han demostrado ser capaces de reducir el consumo de combustible, así como también la emisión de partículas, los óxidos de carbono, los óxidos de nitrógeno, el hollín y los hidrocarburos no quemados, convirtiéndose en un estándar en la industria. Esta tesis presenta una metodología experimental para estudiar los efectos de dos estrategias diferentes de inyección múltiple (piloto-principal y principal-post) sobre el desarrollo fundamental y la combustión del chorro. Primero, se caracterizó hidráulicamente el inyector midiendo su tasa de inyección y flujo de cantidad de movimiento. Para una masa inyectada objetivo, se obtuvo la distribución de combustible para los diferentes tiempos de separación y las cantidades de piloto/post. Se implementó un nuevo enfoque para evaluar la distribución de combustible utilizando la señal de flujo de cantidad de movimiento. Se pudo observar que las inyecciones de piloto/post que se realizan en un estado totalmente transitorio presentan mayor desviación entre disparos. El aumento de la cantidad inyectada redujo la dispersión, con un ligero descenso al disminuir también la presión del rail. La repetibilidad de las inyecciones post se vio afectada significativamente por el tiempo de separación entre pulsos. Luego, se aplicaron diagnósticos ópticos de alta velocidad para visualizar el desarrollo del chorro en atmósferas tanto inerte como reactiva. Se utilizaron dos nuevas soluciones de procesado de imágenes: una para desacoplar dos eventos de inyección que coexisten en un solo cuadro, y otra para estimar el tiempo de retraso al autoencendido de múltiples inyecciónes. En cuanto al desarrollo del chorro en condiciones inertes, no se observó ninguna influencia en la longitud líquida estabilizada y el ángulo del chorro, respecto a la cantidad inyectada por la piloto, ni de su separación al pulso principal. Con respecto a la fase vapor, el aumento de la masa inyectada del primer pulso empujó la zona de transición más allá del límite óptico. En general, el segundo pulso penetró a una mayor velocidad, comparado con el caso de una inyección única. El ángulo de dispersión de la fase de vapor aumentó con la inclusión de la inyección piloto, pero no se observó una tendencia clara con respecto a la cantidad de la piloto ni a su tiempo de separación. En cuanto al desarrollo del chorro en condiciones reactivas, el tiempo de retraso al autoencendido del segundo pulso disminuyó en referencia a su inicio de inyección. En promedio, las estrategias piloto-principal vieron reducciones del 30% al 40%, mientras que las principal-post del 40% al 50%. Con respecto a la longitud de despegue estabilizada, no se observó una tendencia definida con respecto a los efectos tanto del tiempo de separación como de la cantidad de la piloto. La imagen promedio tomada por la cámara intensificada no consideró que la longitud de despegue puede cambiar desde el inicio de la combustión hasta el establecimiento de la llama de difusión. En general se observó que las estrategias piloto-principal producen más hollín que cada uno de sus casos de referencia. Se observó una ligera disminución en el grosor óptico de la sección transversal cerca del inicio de la combustión al aumentar la masa de la piloto. No se observó una clara dependencia del hollín con respecto al tiempo de separación entre pulsos. En contraste a la literatura, las estrategias principal-post mostraron una formación de hollín ligeramente más alta (o similar) que una sola inyección. En cámaras de combustión con un volumen tan grande, la post / [CA] En els últims anys, l'evolució de les tecnologies d'injecció ha permés no només millorar el procés de mescla, sinó també controlar amb precisió els paràmetres d'injecció, afegint flexibilitat als sistemes per a noves estratègies i un grau addicional de complexitat per als investigadors. A més a més, amb les estratègies d'injeccions múltiples s'ha demostrat la possibilitat de reduir el consum de combustible, així com les partícules, els òxids de carboni, els òxids de nitrogen, el sutge i els hidrocarburs no cremats; a més, aquestes estratègies s'han convertit en un estàndard en la indústria. Aquesta tesi estudia els efectes de dues estratègies diferents d'injecció múltiple (pilot-principal i principal-post) sobre el desenvolupament fonamental i la combustió del doll. Primer, es caracteritzar hidràulicament l'injector, mesurant la seua taxa d'injecció i flux de quantitat de moviment. Per a una massa injectada objectiu, es va obtindre la distribució de combustible per als diferents temps de separació i les quantitats de pilot/post. Es va implementar un nou enfocament per tal d'avaluar la distribució de combustible utilitzant el senyal de flux de quantitat de moviment. Es va poder observar que les injeccions de pilot/post injecció que es realitzen en un estat totalment transitori presenten major desviació entre trets. L'augment de la quantitat injectada va reduir la dispersió, observant un lleuger descens en disminuir també la pressió de rail. La repetitivitat de les injeccions post es va veure afectada significativament pel temps de separació entre polsos. Després, es van aplicar diagnòstics òptics d'alta velocitat per a visual-itzar el desenvolupament del doll en atmosferes tant inerts com reactives. Es van utilitzar dues noves solucions de processament d'imatges: una, per a desacoblar dos esdeveniments d'injecció que coexisteixen en un sol quadre, i una altra per a estimar òpticament el retard a l'encesa amb múltiples polsos d'injecció. Pel que fa al desenvolupament del doll en condicions inerts evaporatives, no es va observar cap influència en la longitud líquida estabilitzada i l'angle del doll respecte a la quantitat injectada per la pilot, ni de la seua separació al pols principal. Pel que fa a la fase de vapor, l'augment de la massa injectada del primer pols va empényer la zona de transició més enllà del límit òptic. En general, el segon pols va penetrar a una velocitat més gran comparat amb el cas d'una injecció única. L'angle de dispersió de la fase de vapor va augmentar amb la inclusió de la injecció pilot, però no es va observar una tendència clara pel que fa a la quantitat de la pilot ni al seu temps de separació. En condicions reactives, el retard d'encesa del segon pols va disminuir en referència a l'inici de la injecció. De mitjana, les estratègies pilot-principal van experimentar reduccions del 30% al 40%, mentre que les principal-post, es van veure reduides entre el 40% i el 50%. Pel que fa a la longitud d'enlairament estabilitzada, no es va observar una tendència definida pel que fa als efectes tant del temps de separació com de la quantitat de la injecció pilot. La imatge mitjana presa per la càmera intensificada no va considerar que la longitud d'enlairament puga canviar des de l'inici de la combustió fins a la flama de difusió establerta. Pel que fa als mesuraments de sutge, en general es va observar que les estratègies pilot-principal van produir més sutge que cadascun dels seus casos de referència. Es va observar una lleugera disminució en el gruix òptic de la secció transversal prop de l'inici de la combustió en augmentar la massa de la injecció pilot. No es va observar una clara dependència del sutge amb el temps de separació entre els pols. En contrast amb la literatura, les estratègies principal-post van mostrar una formació de sutge lleugerament més alta (o similar) que una sola injecció. En cambres amb un volum tan / [EN] In recent years, the evolution of the injection technologies has permitted not only to improve the spray mixing process but to control injection parameters accurately, adding flexibility to the systems for new strategies and an extra degree of complexity for researchers. In such sense, multiple injection strategies have proved capable of reducing fuel consumption, as well as emissions of particulate matter, carbon oxides, nitrogen oxides, soot, and unburned hydrocarbons, and has become a standard in the industry. This thesis provides an experimental methodology to study the effects of two different multiple injection strategies (pilot-main and main-post) on spray development and combustion. Experiments were divided into four separate measurement campaigns carried out in three facilities. In the first two campaigns, the injector was hydraulically characterized by rate of injection and spray momentum flux measurements. For a target injected mass, the fuel allocation was obtained for the different dwell times and pilot/post quantities. A new approach to evaluate the fuel distribution using the momentum flux signal was implemented. Higher shot-to-shot deviations were observed for the pilot/post pulses that are injected in an entirely transitory state. The dispersion decreased with increasing injected quantity, and also slightly with decreasing rail pressure. The repeatability of the post injections was significantly affected by the dwell time. Then, high-speed optical diagnostics were applied to visualize the spray development in both inert and reactive atmospheres. Two novel image processing solutions were developed: one to decoupled two injection events that coexist in a single frame, and another to optically estimate the ignition delay of multiple injection pulses. On the spray development in non-reactive conditions, no influence was observed from the injected quantity of the pilot and its dwell time to the main pulse on the stabilized liquid length and spreading angle. Regarding the vapor phase, increasing the injected mass of the first pulse pushed the interaction zone past the optical limit. In general, the second pulse penetrated at a faster rate than the single injection case. Vapor phase spreading angle increased with the inclusion of a pilot injection. No clear trend was observed with either the pilot quantity nor the dwell time. On the spray development in reactive conditions, for all test points that included multiple injections, the ignition delay of the second pulse decreased referenced to its start of injection. On average, pilot-main strategies showed reductions of 30% to 40%, while main-post of 40% to 50%. Different inter-action mechanism found in the literature were used to describe the synergy between injection pulses. Regarding the stabilized lift-off length, no definite trend was observed in terms of the effects of both the dwell time and pilot quantity. The average image taken by the ICCD camera did not consider that the lift-off length can change from the inception of combustion to the established diffusion flame. Regarding soot measurements, it was generally observed that pilot-main strategies produced more soot than each of their reference case. A slight decrease in the cross-sectional optical thickness near the start of combustion was noted increasing the pilot quantity. No clear dependence of soot on the dwell time was observed. In contrast to the literature, main-post strategies depicted slightly higher (or similar) soot formation than a single injection. In combustion chambers with such large volume, the post injection behaved like a main and the actual main like a pilot. Thus, local conditions enhance the formation of soot from the post injection, instead of promoting its oxidation. Therefore, jet-wall interactions are critical for the effectiveness of the post injection on reducing soot emissions. / Viera Sotillo, AA. (2019). Effect of multiple injection strategies on the Diesel spray formation and combustion using optical diagnostics [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/123954

La marée interne contribue au maintien de la circulation méridienne de renversement. Il existe, à l'heure actuelle, une controverse sur la nature exacte des mécanismes pilotant cette circulation. Une meilleure quantification des apports énergétiques associés aux ondes internes permettrait d'apporter quelques clés de compréhension de ce mécanisme complexe. Dans cette thèse, différents régimes d'ondes internes topographiques inspirés par des congurations océaniques sont étudiés an d'évaluer quantitativement les transferts énergétiques associés. L'utilisation complémentaire des outils numériques et expérimentaux permet de détailler la dynamique de ces régimes de manière exhaustive. La première partie de la thèse porte sur la génération d'ondes internes linéaires par l'oscillation d'un mont Gaussien dans un fluide linéairement stratifié. L'approche choisie s'appuie sur un jeu d'expériences de laboratoire pour lesquelles la pente relative du rayon d'onde interne par rapport à la pente maximale du mont varie. Nous montrons qu'un maximum énergétique est atteint dans le régime critique pour lequel les pentes du rayon et du mont sont similaires. Dans la suite de la thèse, la dynamique d'ondes internes de forte amplitude se propageant dans des régions de fort gradient de densité, comme la pycnocline océanique, est étudiée. Nous utilisons dans un premier temps le modèle numérique Symphonie-NH pour décrire leur génération et leur dynamique, sur une configuration académique bidimensionnelle. Tout d'abord, la génération primaire d'ondes internes interfaciales est étudiée. On s'intéresse en particulier à des régimes fortement non-linéaires pour lesquelles des ondes solitaires sont observées. Elle sont induites par l'interaction directe entre la marée barotrope et la topographie et est observée dans des régimes de pycnocline de forte intensité dans l'océan, comme en mer de Sulu. La structure des ondes internes solitaires est étudiée avec des modèles analytiques simples comme l'équation KdV. En modifiant la forme du mont, un contrôle topographique important de la génération primaire d'ondes internes solitaires est observé. Un paramètre adimensionné est proposé pour décrire ce contrôle. Ensuite, la génération secondaire d'ondes internes solitaires induites par l'interaction de rayons d'ondes internes émis sur une topographie avec une pycnocline d'intensité modérée, comme dans le Golfe de Gascogne, est étudiée. Des simulations numériques directes sont effectuées pour décrire la dynamique des ondes internes solitaires, et leur atténuation par radiation d'énergie dans la couche inférieure. L'évolution de la structure des modes normaux en fonction de l'intensité de la pycnocline, et le rôle joué par la forme du mont sont détaillés. Des expériences sont menées pour étudier la génération primaire et la génération secondaire d'ondes internes solitaires dans le grand canal du CNRM-GAME. Une configuration expérimentale utilisant un mont sinusoïdal oscillant dans la couche inférieure, stratifée ou non, d'un fluide bicouche est adoptée. Cette configuration, inspirée des simulations numériques précédentes, permet d'explorer une gamme plus large de régimes d'ondes interfaciales. Des mesures de déplacement interfacial avec des sondes à ultrasons d'une part, et avec des mesures optiques d'autre part, permettent de discuter la dynamique, et la structure tridimensionnelle de ces ondes. La structure des ondes internes solitaires dans le cas de la génération primaire apparaît plus stable que pour la génération secondaire. Dans ce deuxième cas, des structures transverses régulières sont mesurées.

Shock Boundary Layer Interactions (SBLIs) and shock-shock interactions are some of the most fundamental problems in high speed aerodynamics. These interactions are of particular importance in scramjet intakes at hypersonic speeds. In hypersonic own with strong SBLI accompanied by own separation, large separation bubbles can form due to high impinging shock strengths. While experiments involving large separation lengths for the impinging shock boundary layer interactions near sharp leading edge are well documented in the literature, only few investigations on the effect of leading edge bluntness on the interactions are studied. In the present study, experiments were carried out to study the role of leading edge bluntness on the impinging shock boundary layer interactions. An oblique shock generated by a wedge (wedge angle 31 degrees) is made to impinge on a at plate (length 200 mm) over which a boundary layer develops. Different leading edge inserts were used on a at plate to get either a sharp or a blunt (radii from 2 to 8 mm) leading edge. The position of the at plate was moved horizontally with respect to the wedge to vary the shock impingement location relative to the leading edge. Experiments were carried out at two freestream conditions - Mach 5.88 (total enthalpy of 1.26 MJ/kg and freestream Reynolds number of 3.85 million per meter) and Mach 8.54 (total enthalpy of 1.85 MJ/kg and freestream Reynolds number of 1.41 million per meter). The various features of the interaction along with different parameters were obtained from schlieren visualizations and surface pressure measurements. The schlieren visualization was used to obtain the separation length, while the reattachment pressure was obtained from the surface pressure distribution. From the present experimental study, a reduction in separation length was observed with an increase in leading edge bluntness. It was also seen that the sharp leading edge had the maximum separation length. Correlations for the separation length and the reattachment pressure have been proposed for these experimental conditions. Numerical simulations were also carried out using commercial software and they had a qualitative agreement with the experiments.

In 21 century finned surfaces are used in almost all condensers to enhance their heat transfer capabilities. A lot of different models are presented in the literature: on horizontal and vertical finned tubes, inside finned tubes. The validation method of the theoretical models is based on comparison between measurement of average heat transfer coefficient and one calculated by the model. But in this case it is impossible to validate all approaches made in the theory.<p>\ / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The motion of shock waves is important in many fields of engineering and increasingly so with medical applications and applications to inertial confinement fusion technologies. The flow structures that moving shock waves create when they encounter a change in area is complex and can be difficult to understand. Previousresearchers have carried out experimental studies and many numerical studies looking at this problem in more detail. There has been a discrepancy between numerical and experimental work which had remained unanswered. One of the aims of this project is to try and resolve the discrepancy between numerical and experimental work and try to investigate what experimental techniques are suitable for work of this type and the exact way in which they should be applied. Most previous work has focused on sharp changes in geometry which induce immediate flow separation. In this project rounded corners will also be investigated and the complex flow features will be analyzed.Two geometries, namely a sharp 172 degree knife-edge and a 2.8 mm radius rounded corner will be investigated at three experimental pressure ratios of 4, 8 and 12 using air as the driver gas. This yields experimental shock Mach numbers of 1.28, 1.46 and 1.55. High-speed schlieren and shadowgraph photography with varying levels of sensitivity were used to qualitatively investigate the wave structures. Particle image velocimetry (PIV), pressure-sensitive paint (PSP) and traditional pressure transducers were used to quantify the flow field. Numerical simulations were performed using the commercial package Fluent to investigate the effect of numerical schemes on the flow field produced and for comparison with the experimental results. The sharp geometry was simulated successfully using an inviscid simulation while the rounded geometry required the addition of laminar viscosity. Reynolds number effects will be only sparsely referred to in this project as the flows under investigation show largely inviscid characteristics. As the flow is developing in time rather than in space, quotation of a distance-based Reynolds number is not entirely appropriate; however, Reynolds number based on the same spatial location but varying in time will be mentioned. The density-based diagnostics in this project were designed to have a depth of field appropriate to the test under consideration. This approach has been used relatively few times despite its easy setup and significant impact on the results. This project contains the first quantative use of PIV and PSP to shock wave diffraction. Previous studies have almost exclusively used density-based diagnostics which, although give the best impression of the flow field, do not allow for complete analysis and explanation of all of the flow features present. PIV measurements showed a maximum uncertainty of 5% while the PSP measurements showed an uncertainty of approximately 10%.The shock wave diffraction process, vortex formation, shear layer structure, secondary and even tertiary expansions and the shock vortex interaction were investigate. The experimental results have shown that using one experimental technique in isolation can give misleading results. Only by using a combination of experimental techniques can we achieve a complete understanding of the flow field and draw conclusions on the validity of the numerical results. Expanding the range of the experimental techniques currently in use is vital for experimental aerodynamic testing to remain relevant in an industry increasingly dominated by numerical research. To this end, significant research work has been carried out on extending the range of the PSP technique to allow for the capture of shock wave diffraction, one of the fastest transient fluid processes, and for applications to low-speed flow (< 20 ms−1).

The diploma thesis deals with problems of laser welding in shielding gases. On the basis of theoretical knowledge in this thesis, was made welding an experiment of 10 samples of steel X5CrNi18-10 in two different shielding gases. Flow of shielding gases has been shown by schlieren method. On the samples of welding joints have been made mechanical tests (tensile test and hardness test). Welded joints were metallography evaluated and structure of them was confirmed by measurements on ferrite meter.

No description available.