Crackle is a perceptual feature of supersonic jet noise that is related to the presence of acoustic shocks. The skewness of the time-derivative of the pressure waveform, or derivative skewness, is used as a metric indicative of crackle perception. The three main objectives of this work are: 1) Determine the potential spatial origin of crackle-related events in the near field of a high-performance military aircraft via an event-based beamforming method. 2) Investigate the potential for nonlinear, irregular shock reflections occurring along the near-field ground array and their implications on derivative skewness. 3) Relate the near-field, crackle-related events to far-field crackle perception by comparing nonlinearly propagated waveforms with measured far-field data. The event-based beamforming method used to determine source and far-field relationship of shock-like events utilizes the cross correlation between adjacent microphone waveform segments to determine the angle of propagation for an ensemble of crackle-related events within the waveform. The angle of propagation is traced towards the source for each event to find its apparent origin along the jet lipline. Beamforming results indicate that crackle-related events appear to originate anywhere from 2 to 14.5 m downstream along the jet lipline, with distributions that shift downstream and broaden with increasing engine power. The shock reflection classification method builds on the event-based beamforming method to calculate angle of incidence relative to the ground for an ensemble of shock events. The combination of angles of incidence and the measured shock strengths of the events reveal that irregular reflections are likely to occur over the majority of the array, which likely elevates the derivative skewness values due to steeper shocks with greater peak-to-peak pressures relative to off-ground measurements. Near-field, crackle-related events are extrapolated to the far field using a nonlinear propagation model to determine their prevalence in the far field. Cross-correlation coefficients of waveform segments centered about the propagated events indicates that for farther aft angles, near-field events are more related to far-field measurements. Waveform observations show that shock-like events in the near field that are more spiked in nature tend not propagate into the far field. However, near-field, large-derivative events with broader, high-pressure peaks nonlinearly steepen and form shocks in the far field that are likely contribute to crackle perception.

Nonlinear propagation and shock formation are shown in noise radiated from full-scale military jet aircraft. Perception of sound is not only affected by the overall sound pressure level of the noise, but also characteristics of the sound itself. In the case of jet noise, acoustic shocks within the waveforms result in a characteristic commonly referred to as"crackle." The origin of shocks in the far-field of jet noise is shown to be through nonlinear propagation. Metrics characterizing the shock content of a waveform are explained and given physical significance, then applied to jet noise at various distances and engine conditions to show areas where shock formation is significant. Shocks are shown to develop at different distances from the aircraft, dependent on the amplitude and frequency, and nonlinear propagation is shown to be important in determining time and frequency characteristics of jet noise at distances of up to 1220 m from the aircraft. The shock content is also characterized during flyover experiments, and the shock content between the two scenarios is compared. While some reduction in overall level and shock content is seen in the maximum radiation region, level increases in the forward direction during flight result in increased shock content. Variation at distances of 305 m and beyond is considered and shown as a result of small atmospheric changes. Finally, a nonlinear numerical propagation scheme is used to model the propagation, showing accuracy in predicting frequency-domain and time-domain features that are evidence of nonlinear propagation.

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Dans ce travail de thèse, les mécanismes à l'origine de la formation des chocs associés à la perception de crackle proche de jets supersoniques axisymétriques sont étudiés à l'aide de simulations numériques. Dans ces simulations, les équations de Navier-Stokes instationnaires et compressibles sont résolues en coordonnées cylindriques à l'aide de différences finies d'ordre élevé peu dissipatives et peu dispersives. Quatre jets temporels à des nombres de Mach de 2 et~3 et à des nombres de Reynolds compris entre 3125 et 50000 sont simulés dans un premier temps. Des ondes acoustiques de forte amplitude présentant d'importants gradients de pression sont mises en évidence à proximité des jets. Elles se forment par un mécanisme de raidissement à la source qui est étudié par le calcul de moyennes conditionnelles synchronisées autour des pics de pression en champ proche. Ces moyennes montrent un lien direct entre ces ondes non linéaires et la convection de structures cohérentes à desvitesses supersoniques dans les couches de~mélange. L'influence de la température sur la formation de ces ondes est examinée dans un second temps par le calcul de cinq jets temporels à des rapports de température de 1, 2 et 4, et à des nombres de Mach acoustique compris entre 2 et 4. À vitesse d'éjection constante, les niveaux de bruit produits par les jets chauds sont moins élevés que ceux du jet isotherme, mais les ondes non linéaires qu'ils rayonnent sont peu affectées par une hausse de température. À nombre de Mach constant, les niveaux augmentent avec la température, de même que l'asymétrie des fluctuations de pression, traduisant un renforcement du caractère non linéaire des ondes rayonnées. Ces variations pourraient être dues à celles de la vitesse de convection des structures cohérentes, qui augmente de façon significative avec la température lorsque le nombre de Mach est constant, mais diminue légèrement à vitesse~constante. Finalement, trois simulations de jets spatiaux isothermes et chauds à un nombre de Mach acoustique de 2 et à des nombres de Reynolds de 12500 et 50000 sont mises en \oe uvre. Des ondes de Mach présentant d'importants gradients de pression sont visibles au voisinage direct des jets. La formation de ces ondes est liée, comme dans le cas des jets temporels, à la convection supersonique de structures cohérentes dans les couches de mélange. Le champ lointain acoustique est enfin déterminé par des méthodes d'extrapolation linéaire et non linéaire. Lorsque la propagation est non linéaire, un raidissement additionnel des fronts d'onde est constaté en champ lointain. / Numerical simulations are carried out with the aim of investigating the formation of nonlinear steepened waves at the origin of crackle in the near acoustic field of supersonic jets. In these simulations, the compressible Navier-Stokes equations are solved in cylindrical coordinates using high-order low-dissipative and low-dispersive finite difference schemes.Four temporally-developing isothermal round jets are first simulated at Mach numbers of~2 and~3 and at Reynolds numbers ranging from 3,125 to 50,000. Strong acoustic waves containing sharp pressure variations are observed in the vicinity of the jets. Their formation process is described by the computation of conditional averages which are triggered by the detection of strong pressure peaks in the near field. Such steepened waves are then shown to be produced by the supersonic motion of coherent structures inside the jet shear layers.Temperature effects are then investigated by considering five temporal round jets at temperature ratios of 1, 2 and~4 and at acoustic Mach numbers of 2, 2.8 and 4. For a given jet speed, the sound levels produced by the hot jets are lower than those of the isothermal one. However, the properties of the steepened waves they generate are not significantly affected by a rise of temperature. On the contrary, when the Mach number is held constant, pressure levels are higher at high temperature. The skewness and kurtosis factors of pressure fluctuations are also increased, which indicates a strengthening of the asymmetry and the intermittency of the pressure fluctuations. It is likely that the influence of temperature on these waves results from the variations of the convection speed, which is found to significantly increase with temperature at constant Mach number, but to slightly decrease at constant jet speed.Finally, three simulations of spatially-developing axisymmetric, isothermal and hot jets at a Mach number of~2 and at Reynolds numbers of 12500 and 50000 are performed. Strong Mach waves possessing the distinctive features of crackle are visible in the near vicinity of the jets. As observed for temporal simulations, their formations are associated with the supersonic motion of large-scale coherent structures inside the jet shear layers. The far acoustic field is determined using linear as well as nonlinear extrapolation methods. When nonlinear propagation effects are taken into account, a further steepening of the wavefronts is observed with increasing propagation distance.

Dans les arts plastiques, le concept de la beauté doit être associé aux techniques sous-jacentes. L'artiste doit choisir et maîtriser ces techniques afin de les appliquer à l'art en vue d'atteindre les résultats esthétiques visés. Une approche scientifique de ces techniques a un rôle important dans l'amélioration de leur application dans les arts plastiques. Les céramiques et poteries sont un domaine complexe où les réactions chimiques et les propriétés physiques des argiles et des glaçures doivent être prises en compte. Dans ce domaine l'histoire de la science était un guide utile dans une telle recherche. Pour les céramiques, les réactions chimiques se produisant à la phase haute température du processus de cuisson déterminent essentiellement l'aspect final de la surface du produit. En conséquence, changer les conditions de ces réactions (profils de température, la nature de l'atmosphère du four) était une bonne méthode pour obtenir de nouveaux aspects de surface. L'atmosphère du four pendant et après la cuisson permettait de contrôler, dans une large mesure, l'aspect final des produits céramiques, et cela dépend à la fois de la conception et de la mise en place du four. L'étude de l'histoire des techniques céramiques, dans différentes civilisations, a conduis à un aperçu des techniques de cuisson. La compréhension scientifique de ces techniques a mené à des stratégies en vue de modifier la conception du four et la pratique de la cuisson. / In Plastic arts; with the concept of beauty there are also techniques, artists choose between these techniques for apply art works matching with aesthetic viewpoint. As well as science have important role in improved applied arts and fine arts techniques. In ceramics and pottery we are confronted with the chemicals reactions and physical properties of clay and glaze which have deep roots in human history, so history techniques will guide us in this research. In ceramic, chemical reactions need high temperature as condition to exist (Firingprocess), and that have main role in determined final appearance of surface treatments for ceramics forms. When the chemical reactions and physical properties which happen in firing process are responsible of final appearance and aesthetics treatments of ceramics forms, the changing of reactions conditions was used for achieving new treatments for ceramic surface beauty. The atmosphere of kiln during and after firing process whom decide the final appearance for ceramics forms, presented as technique for modifying kiln structure as afactor of enriching aesthetics treatments for ceramic surface. The history and science of ceramics techniques in some civilizations was studied to understand some firing techniques and its roles in ceramic surface esthetics. These provided evidence with experimental study to design a new kiln which can be used as a tool to enrich ceramics forms aesthetically