Academic literature on the topic 'Background Oriented Schlieren'
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Journal articles on the topic "Background Oriented Schlieren"
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Meier, G. "Computerized background-oriented schlieren." Experiments in Fluids 33, no. 1 (July 2002): 181–87. http://dx.doi.org/10.1007/s00348-002-0450-7.
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Cozzi, F., and E. Göttlich. "Enhanced Background Oriented Schlieren (EBOS)." Journal of Physics: Conference Series 1249 (May 2019): 012017. http://dx.doi.org/10.1088/1742-6596/1249/1/012017.
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Klemkowsky, Jenna N., Timothy W. Fahringer, Christopher J. Clifford, Brett F. Bathel, and Brian S. Thurow. "Plenoptic background oriented schlieren imaging." Measurement Science and Technology 28, no. 9 (August 21, 2017): 095404. http://dx.doi.org/10.1088/1361-6501/aa7f3d.
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Hargather, Michael John, and Gary S. Settles. "Natural-background-oriented schlieren imaging." Experiments in Fluids 48, no. 1 (July 9, 2009): 59–68. http://dx.doi.org/10.1007/s00348-009-0709-3.
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OTA, Masanori, Friedrich LEOPOLD, Frederique AGUSINSKI, and Kazuo MAENO. "0405 A Comparison of Measurement Results for Supersonic Flow Field by Colored-Grid Background Oriented Schlieren(CGBOS)andColored Background Oriented Schlieren (CBOS) Technique." Proceedings of the Fluids engineering conference 2012 (2012): 199–200. http://dx.doi.org/10.1299/jsmefed.2012.199.
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Elsinga, G. E., B. W. van Oudheusden, F. Scarano, and D. W. Watt. "Assessment and application of quantitative schlieren methods: Calibrated color schlieren and background oriented schlieren." Experiments in Fluids 36, no. 2 (November 22, 2003): 309–25. http://dx.doi.org/10.1007/s00348-003-0724-8.
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Davis, Jenna K., Christopher J. Clifford, Dustin L. Kelly, and Brian S. Thurow. "Tomographic background oriented schlieren using plenoptic cameras." Measurement Science and Technology 33, no. 2 (December 7, 2021): 025203. http://dx.doi.org/10.1088/1361-6501/ac3b09.
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Abstract The development of a tomographic background oriented schlieren implementation system utilizing up to four plenoptic cameras is presented. A systematic set of experiments was performed using a pair of solid dimethylpolysiloxan cylinders immersed in a nearly refractive index matched gylcerol/water solution to represent discrete flow features with known sizes, shapes, separation distances, and orientation. A study was conducted to assess the influence of these features on the accuracy of 3D reconstructions of the refractive index field. It was determined that the limited angular information collected by a single plenoptic camera is insufficient for single-camera 3D reconstructions. In multi-camera configurations, the additional views collected by a plenoptic camera were shown to improve the overall reconstruction accuracy compared to an equivalent single view per camera reconstruction, potentially reducing the number of overall cameras needed to achieve a desired accuracy. For the imaging of two cylinders, three or more cameras are generally needed to avoid significant ghosting artifacts in the reconstruction. Quantitative results are presented that show that: (1) two separate cylinders will be individually resolved as long as measurements from one camera are able to observe separation between the cylinders; (2) the error in the reconstructed 3D refractive index field increases as the size of the feature decreases; and (3) the use of volumetric masking within the reconstruction algorithm is critical in order to improve the accuracy of the solution.
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Koponen, Eero, Jarkko Leskinen, Tanja Tarvainen, and Aki Pulkkinen. "Background-oriented schlieren sensitivity in terms of geometrical parameters of measurement setup." Journal of the Acoustical Society of America 154, no. 6 (December 1, 2023): 3726–36. http://dx.doi.org/10.1121/10.0023949.
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Background-oriented schlieren imaging is a recently proposed noninvasive optical method for imaging of full ultrasound fields. In this work, the impact of uncertainty in geometrical parameters of a background-oriented schlieren measurement setup for imaging of full ultrasound fields is studied using numerical simulations. The studied parameters are focal length of the camera and positions and orientations of the camera, water tank, and ultrasound field. The results demonstrate that the most sensitive parameters affecting the accuracy of the reconstructed ultrasound fields are the orientations of the camera that change the direction of an effective optical axis. Other sensitive parameters are the focal length of the camera and the position of the ultrasound field in perpendicular directions of an optical axis. This synthetic study demonstrates the accuracy requirements for calibrating the geometrical parameters of a measurement setup that would be required to achieve accuracy comparable to that of hydrophone measurements using the background-oriented schlieren imaging. Explicitly, limits of the variation ranges of the geometrical parameters resulting in relative error ranges of 5% and 10% are given. The results of this study may contribute to help design future background-oriented schlieren measurement setups intended for measurement of full ultrasound fields.
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Jia, Tong, Jiawei Li, Jie Wu, and Yuan Xiong. "Tomographic Background-Oriented Schlieren for Axisymmetric and Weakly Non-Axisymmetric Supersonic Jets." Symmetry 16, no. 5 (May 11, 2024): 596. http://dx.doi.org/10.3390/sym16050596.
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The Schlieren technique is widely adopted for visualizing supersonic jets owing to its non-invasiveness to the flow field. However, extending the classical Schlieren method for quantitative refractive index measurements is cumbersome, especially for three-dimensional supersonic flows. Background-oriented Schlieren has gained increasing popularity owing to its ease of implementation and calibration. This study utilizes multi-view-based tomographic background-oriented Schlieren (TBOS) to reconstruct axisymmetric and weakly non-axisymmetric supersonic jets, highlighting the impact of flow axisymmetry breaking on TBOS reconstructions. Several classical TBOS reconstruction algorithms, including FDK, SART, SIRT, and CGLS, are compared quantitatively regarding reconstruction quality. View spareness is identified to be the main cause of degraded reconstruction quality when the flow experiences axisymmetry breaking. The classic visual hull approach is explored to improve reconstruction quality. Together with the CGLS tomographic algorithm, we successfully reconstruct the weakly non-axisymmetric supersonic jet structures and confirm that increasing the nozzle bevel angle leads to wider jet spreads.
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Wernet, Mark P. "Real-time background oriented schlieren with self-illuminated speckle background." Measurement Science and Technology 31, no. 1 (October 28, 2019): 017001. http://dx.doi.org/10.1088/1361-6501/ab4211.
Full textDissertations / Theses on the topic "Background Oriented Schlieren"
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Jong, Edmund Chime. "Application of Background Oriented Schlieren (BOS) in Underground Mine Ventilation." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32242.
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The schlieren technique describes an optical analysis method designed to enhance light distortions caused by air movement. The ability to visualize gas flows has significant implications for analyzing underground mine ventilation systems. Currently, the widely utilized traditional schlieren methods are impractical underground due to complex equipment and design requirements. Background oriented schlieren (BOS) provides a solution to this problem. BOS requires two primary components, a professional quality digital camera and a schlieren background. A schlieren background is composed of a varying contrast repetitive pattern, such as black and white stripes or dots. This background allows the cameraâ s sensor to capture the minor light diffractions that are caused by transparent inhomogeneous gases through image correlation. This paper investigates a possible means of mitigating some of the major problems associated with surveying underground mine ventilation systems with the BOS method.
BOS is an imaging technique first introduced in 1999 that allows the visualization of flowing inhomogeneous transparent media. In ventilation surveys, BOS can be used to attain qualitative data about airflows in complex areas and methane emissions from coal. The acquisition of such data would not only enhance the understanding of mine ventilation but also improve the accuracy of ventilation surveys. As an example, surveys can benefit from small scale BOS investigations around fans, regulators, overcasts, and critical junctions to identify effective data gathering positions. Regular inspections of controls and methane monitoring points could also be improved by the systematic nature of BOS.
Computer programs could process images of each location identically regardless of quantity. BOS can then serve as a check to identify items that were overlooked during the routine inspection. Despite the potential of BOS for ventilation analysis, several limitations still exist. These issues are sensitivity threshold and quantification of flow data. This paper specifically examines the qualitative potential of the BOS technique for imaging various underground ventilation flows and outlines initial experimental efforts used for the evaluation.
Three primary experiments were conducted to evaluate BOS as a potential qualitative analysis technique for underground mine ventilation. The first experiment used BOS to image of flow induced by an axial vane fan and an axial flow fan using an artificial background and an imitation rock background. This experiment showed that the BOS system was unable to image isothermal airflow from either fan. Heated airflow could be visualized with both fans using the artificial striped background but not with the imitation rock background. The BOS system lacked the sensitivity necessary to image isothermal airflow from the two fans. The focus of the overall BOS study was changed to explore higher pressure airflows through a regulator.
The second experiment used BOS to image flow through a regulator induced by an axial flow fan using an artificial striped background. The BOS images were compared to ones produced by a traditional schlieren single mirror systems for validation of the BOS experimental design. This experiment was unable to image isothermal airflow through the regulator from either system. However, heated airflow could be visualized by both systems. The BOS and traditional schlieren systems used in this experiment lacked the sensitivity necessary to image isothermal airflow through a regulator. However, the BOS procedures were successfully validated by the ability of both the BOS and traditional schlieren systems to image heated airflows. The focus of the study was changed to explore methane gas emissions.
Numerous mining industry techniques already exist to quantify methane content. However, methane content is different from the actual methane emission rate of exposed coal. Emission rates have been modeled using numerical simulation techniques, but the complexity of the methane migration mechanism still requires physical data to achieve higher accuracy. The third experiment investigated the feasibility of using the BOS technique for imaging methane flow by imaging methane emission from a porous medium. Laboratory grade methane was directly injected into a Brea sandstone core sample using a flexible tube.
The BOS system was successfully able to image methane desorption in this study. A repeating pattern consisting of alternating black and white stripes served as the schlieren background for the Nikon D700 camera. The ability to image methane emission even at low injection pressures (i.e. 20 psi) demonstrates that actual methane desorption from coal can potentially be imaged. This result can only be conjectured because of a lack of research in the area of methane emission. Despite this issue, the experimental results suggest that BOS can be feasibly utilized to image methane emissions from coal in an underground mine.
The results of the three experiment demonstrated that the potential for large scale implementation of BOS in underground mines does exist. Qualitative BOS information has the potential in the practical sense to optimize the procedures of ventilation surveys and design of ventilation monitoring equipment. For example, images of methane flow in active mining areas can be used to optimize the positioning of auxiliary ventilation equipment to dilute known areas of high methane concentration. BOS images could also be used to re-evaluate the placement of methane monitors on mining equipment to better facilitate the detection of dangerous methane concentrations in active mining areas. For these reasons, further investigation into the BOS technique for use in imaging underground airflows with differential temperatures and methane emissions in underground coal mines is suggested as an addendum to this study.Master of Science
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Walter, Léo. "Étude expérimentale et théorique du mélange d'un jet léger." Electronic Thesis or Diss., Toulouse, ISAE, 2024. http://www.theses.fr/2024ESAE0071.
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L'objectif de cette thèse est d'étudier les mécanismes physiques qui gouvernent l'évolution et le mélange des jets latéraux au sein des jets ronds de mélange binaire à faible densité, au moyen d'une double approche numérique et expérimentale. Les mécanismes physiques à l'origine des jets latéraux restent encore incertains et sont en lien direct avec le développement d'instabilités secondaires responsables de la tridimensionalisation de l'écoulement. Ainsi, une meilleure compréhension de ces mécanismes en jeu constitue un prérequis indispensable à la conception d'une stratégie de contrôle qui vise à promouvoir le mélange entre le jet et l'environnement ambiant.L'objectif de l'étude numérique est d'identifier les mécanismes transitoires qui influencent la croissance des perturbations tridimensionnelles dans le jet rond à faible masse volumique, en particulier dans les conditions physiques pour lesquelles apparaissent les jets latéraux. À cet effet, nous mettons en oeuvre une analyse de stabilité linéaire non-modale de l'évolution non-linéaire et axisymétrique de l'anneau tourbillonnaire de Kelvin-Helmholtz qui se développe dans les jets ronds à faible masse volumique en réponse à l'instabilité primaire de Kelvin-Helmholtz. Cette analyse de stabilité est réalisée à l'aide du code académique dalsa qui a été adapté pour ce régime d'écoulement. L'utilisation d'une méthode d’optimisation directe-adjointe permet d'identifier la structure spatiale et l'évolution temporelle des perturbations tridimensionnelles qui maximisent leur gain d'énergie généralisée, ainsi que les mécanismes physiques sous-jacents et leur lien avec l'apparition des jets latéraux. En particulier, l'objectif est d'apporter de nouveaux éléments permettant de statuer entre les deux hypothèses proposées dans la littérature pour expliquer le mécanisme à l'origine des jets latéraux. La première proposée par Monkewitz & Pfizenmaier (1991) repose sur un mécanisme d'induction de vitesse par les tourbillons longitudinaux contra-rotatifs qui se développent dans les écoulement cisaillés à masse volumique constante. La seconde est basée sur le mécanisme de tri-dimensionalisation associé aux stries de vitesse longitudinale de signe opposé qui se développent de part et d'autre du point de stagnation hyperbolique dans la tresse identifiée par Lopez-Zazuetaet al. (2016) dans la couche de mélange plane à densité variable.L'étude numérique conduite dans cette thèse est conçue en lien étroit avec la campagne expérimentale visant à étudier la structure des jets latéraux dans un jet de mélange binaire hélium-air. Ainsi, les paramètres de l'étude numérique comme les nombres de Reynolds et d'Atwood ainsi que le rapport d'aspect du jet, sont basés sur les conditions expérimentales. Ceci permet une comparaison directe des résultats théoriques aux observations expérimentales. Pour ce faire, nous avons conduit une campagne de mesures d'anémométrie à fil chaud du profil radial de vitesse du jet, et de la fréquence de l'instabilité primaire, afin de le caractériser et de le placer dans le contexte de la littérature scientifique.L'objectif de l'approche expérimentale est d'analyser la structure des jets latéraux et le mélange qu'ils induisent. Nous avons ainsi conçu et assemblé un banc de Background Oriented Schlieren tomographique (3DBOS). Ce banc est conçu afin de pouvoir observer les déviations optiques de l'ordre de 0,5 mrad induites par le champ hétérogène d'indices de réfraction créé par le jet de mélange hélium-air. Les mesures de 3DBOS obtenues permettent de reconstruire les champs de masse volumique du jet à faible densité en présence de jets latéraux. Ces champs de masse volumique sont originaux dans la littérature scientifique sur le sujet, et permettent d'augmenter notre compréhension de la structure des jets latéraux et de leur impact sur le mélange, et ainsi de corroborer les prédictions issues de l'analyse de stabilitéThe aim of this PhD thesis is to study the physical mechanisms which govern the evolution and the mixing of side-jets in low-density binary mixing round jets, using a complementary numerical and experimental approach. The physical mechanisms which are responsible for the generation of side-jets, closely related to the three-dimensionalisation of the jet through the development of secondary instabilities, are as of yet not fully understood. As such, a better understanding of the mechanisms at play is a prerequisite for the design of an efficient control strategy to promote the mixing between the jet and ambient fluid.The objective of the numerical study is to identify the transient mechanisms which influence the growth of three-dimensional disturbances in the low-density round jet, specifically under the physical conditions in which side-jets appear. To that aim, a linear non-modal stability analysis was conducted over the non-linear evolution of a two dimensional axisymmetric Kelvin-Helmholtz vortex ring which develops in low-density round jets due to the Kelvin-Helmholtz primary instability.The stability analysis was implemented through further numerical development of the existing dalsa academic code. Through the use of a direct-adjoint optimisation method, we identify the spatial structure and temporal evolution of three-dimensional disturbances which yield the highest growth of generalised energy, as well as the underlying physical mechanisms and their relation to side-jets generation in low-density round jets at low Atwood numbers. In particular, we seek to bring a new perspective in order to settle between the two current hypotheses concerning the physical mechanisms at the origin of side-jets. The first hypothesis suggested by Monkewitz & Pfizenmaier (1991) relies on a velocity induction mechanism induced by the longitudinal counter-rotating vortex dipoles developing in the constant-density case. The second one is based on the three-dimensionalisation mechanism associated with longitudinal velocity streaks of opposite sign developing on either side of the hyperbolic stagnation point in the braid identified by Lopez-Zazueta et al. (2016) in the case of variable-density plane mixing layers.The numerical analysis is conducted in close relation to an experimental investigation of the structure of side-jets in a helium-air binary mixture round jet. The parameters used in the numerical analysis, such as the Reynolds number, the Atwood number and jet aspect ratio, are based on the operating conditions used in the experiment, allowing the theoretical predictions to be compared with the empirical evolution of the helium-air jet. To that aim, we conduct hot-wire anemometry measurements of the jet radial profile and frequency of the primary instability under several operating conditions to characterise the evolution of the governing parameters and relate the experimental conditions to the existing scientific literature.The objective of the experimental investigation is to study the structure of side-jets and their effect on the mixing of the jet and ambient fluids. To do so, we have designed and assembled a tomographic Background Oriented Schlieren (3DBOS) experimental bench. This bench is designed to observe the deviations of light-rays of the order of 0.5 mrad induced by the change in refractive index in the helium-air jet. The 3DBOS technique employed in this study provides novel reconstructions of three-dimensional density maps of the side-jets which develop over the helium-air jet. Through these novel density maps, we can provide new insight into the structure of side-jets and their induced mixing, and relate them to the predictions of the stability analysis
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Benito, Parejo Carlos Javier. "Experimental Characterization of Electrical Discharges and Formation of the Ignition Kernel. Application to the Study of Performances of Aeronautical Igniters." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2019. http://www.theses.fr/2019ESMA0021.
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Les systèmes d'allumage par étincelle sont généralement définis par l'énergie électrique utilisée pour leur fonctionnement. Cependant, la caractéristique physique qui affecte directement le processus d'allumage est l'énergie déposée dans le fluide par le système. Ce travail porte sur le développement de deux méthodologies proposées pour la caractérisation du dépôt d’énergie thermique de décharges électriques produites par différents systèmes d'allumage et de leur mise en œuvre au travers d’une étude paramétrique.Un dispositif expérimental est mis au point afin de développer et mettre en œuvre simultanément les deux techniques: une technique non optique, la calorimétrie à volume constant, et une technique optique, la SBOS (Speckle-based Background-Oriented Schlieren). L’étape de validation de ces méthodes est réalisée dans une configuration de référence d’un allumeur inductif alimentant une paire d'électrodes pointe-pointe.La calorimétrie à volume constant permet de mesurer un dépôt d'énergie thermique fournie au fluide par l’analyse de la montée en pression à l'intérieur d'une chambre de petit volume. Un suivi temporel du dépôt d’énergie pendant la décharge est ainsi obtenu. La mesure globale dans un volume de contrôle rend cette technique adaptable à tous types de décharges et d’électrodes. Le rapport entre le dépôt d'énergie thermique et l'apport d'énergie électrique représente l'efficacité du transfert d'énergie. Cette dernière est comprise entre 15 et 40 % pour la configuration de référence. Le dépôt d'énergie et l'efficacité du transfert d’énergie sont plus élevés à mesure que la pression et l'écart inter-électrode augmentent. Des essais avec un mélange inerte azote-propane montrent que le dépôt d'énergie est plus important en présence de carburant que dans l'air pur.La SBOS est une méthode optique permettant de quantifier les variations d’indice optique générés par le phénomène étudié. Le principe consiste à comparer des images d’un motif visualisé au travers du phénomène avec ce même motif en l’absence de phénomène. Cette technique est ici adaptée aux contraintes d’échelles spatiale et temporelle d’une décharge électrique. Une procédure de traitement a été développée afin d’obtenir les champs de masse volumique, de température et enfin l'énergie locale au moment de l'acquisition de l'image. Le volume du noyau chaud produit par le plasma et le dépôt d'énergie en sont déduits. Ces propriétés sont mesurées à différents instants de l'évolution du noyau. Dans la configuration de référence, il est montré que les températures dans le noyau chaud atteignent des valeurs plus élevées pour des distances inter-électrodes et des pressions plus élevées ou encore en présence de carburant. Le volume du noyau chaud est en revanche réduit lorsque la pression ou la distance inter-électrode augmente. Des mesures simultanées de dépôt d’énergie par les deux techniques montrent un très bon accord entre la SBOS et la calorimétrie.Enfin, les deux méthodologies sont adaptées à l'étude de différents systèmes d'allumage. Ainsi, deux allumeurs ont été testés, un allumeur à décharge radiofréquence multi filamentaires innovant et un allumeur capacitif typique d’un moteur d’hélicoptère. Pour ce dernier, le dépôt d'énergie est mesuré pour différentes pressions initiales et mélanges gazeux afin de simuler les conditions réelles du moteur. La technique SBOS est utilisée pour estimer la température dans le noyau chaud aux premiers instants de la décharge (jusqu'à 3500 K) et le dépôt d’énergie thermique qui est en bon accord avec la mesure calorimétrique. Le rendement ce cette décharge spécifique semble peu dépendant des conditions thermodynamiques du mélange et est estimé à 14%Spark ignition systems are generally defined by the electrical energy input used to operate them. However, the physical characteristic that directly affects the ignition process is the energy deposit supplied to the fluid by the system. This work focuses on the development of two proposed methodologies for the characterization of the thermal energy deposit of electrical discharges produced by different ignition systems, and their implementation through a parametric study. An experimental device is developed for this purpose, using simultaneously a non-optical and an optical technique. The experimental techniques are first validated in a reference configuration: a pair of pin-to-pin electrodes with an automobile-type inductive ignition system.Constant volume calorimetry measures a thermal energy deposit supplied to the fluid via the pressure rise inside a reduced volume chamber. The ratio between thermal energy deposit and electrical energy supply represents the efficiency of energy transfer, which is between 15 and 40% for the reference configuration. Energy deposit and efficiency are higher as pressure and inter-electrode gap increase. Tests with an inert propane-nitrogen mixture show that energy deposit is greater in the presence of fuel than in clean air.SBOS (Speckle-based Background-Oriented Schlieren) is an optical method that quantifies changes in the optical index generated by the phenomenon under study. This technique has been adapted to the spatial and temporal specificity of an electrical discharge. Image-processing procedure has been developed to obtain density, temperature and local energy fields at the time of image acquisition. The volume of the hot kernel produced by the plasma and the energy deposit are deduced from it. These properties are measured at different times during the evolution of the kernel. Temperatures in the hot kernel reach higher values (up to 1400 K) at longer inter-electrode gaps and higher pressures, or in the presence of gaseous fuel. Energy deposit measurements performed by SBOS are in good agreement with calorimetry results.Finally, both methodologies are adapted to the study of different ignition systems. Two igniters were tested: an innovative multi-filament radiofrequency discharge igniter and a capacitive helicopter engine igniter. For the latter, the energy deposit is measured for different initial pressures and gas mixtures to simulate the actual engine conditions. The electrical energy input is 2 J, the electrical energy measured at the electrodes is 625 mJ and finally the thermal energy deposited in the gas is about 85 mJ. The estimated efficiency of 14% is not very pressure dependent. The SBOS technique is used to estimate the temperature in the hot kernel at the first moments of discharge (around 3700 K) and the thermal energy deposit, which is in good agreement with the calorimetric measurement
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BIGANZOLI, ILARIA. "Characterization of atmospheric pressure plasmas for aerodynamic applications." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/53249.
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The use of plasmas in aerodynamics has become a recent topic of interest. In particular, over the last ten years, plasma actuation has received much attention as a promising active method for airflow control. Flow control consists of manipulating the properties of a generic moving fluid with the aim of achieving a desired change, but flow dynamics in proximity of a solid object is usually considered, being a consistent and significant issue in many engineering applications, such as engine, automobile or airplane design. Plasma control of airflows along surfaces has been the subject of several experimental studies whose aim was to reduce turbulence, to decrease drag, to enhance airfoil lift or to prevent flow detachment. The fast temporal response and the absence of moving parts are the most promising features from which plasma actuators could benefit.
Different types of plasma sources are currently studied as good candidates for plasma actuation, but Dielectric Barrier Discharges (DBDs) are usually preferred, being characterized by the presence of an insulating barrier between the electrodes. This allows the generation of a non-thermal plasma at atmospheric pressure and prevents the discharge from collapsing into an arc. Surface Dielectric Barrier Discharges (SDBDs) are particularly suitable for these kinds of applications, since plasma is created by ionizing a thin portion of air nearby the surface of the dielectric barrier and this can effectively influence the local properties of the boundary layer associated to an external flow.
This thesis deals with SDBDs in an asymmetric configuration where one electrode is glued into an insulating material and to other one is exposed to air, so that plasma is created in correspondence of just one side of the dielectric barrier. The buried electrode is connected to the ground, whereas a sinusoidal high-voltage is applied to the exposed one. It has been noticed that, when these discharges are operated in quiescent air, an airflow of several metres per second is observed above the dielectric sheet and near the plasma region. This is usually called ionic wind because the main mechanism responsible for its generation is believed to be momentum transfer from the ions drifting in the discharge electric field to the surrounding fluid, by particle-particle collisions.
When the electric field imposed by the voltage difference between the electrodes is sufficiently high, plasma is created and electrical charges are transported through the gap and accumulated on the insulating surfaces. This charge accumulation generates an electric field that locally weakens the external one. When the total electric field falls below the threshold necessary for plasma ignition, the discharge extinguishes. If the voltage imposed to the fed electrode is increased, the discharge can be locally initiated again, and that is the reason why a sinusoidal high-voltage supply is adopted instead of a continuous one. Consequently, the presence of the insulating barrier usually leads to a regime where charge is mainly transported in sub-millimetre regions consisting of current filaments with temporal duration limited to a few tens of nanoseconds. These plasma microdischarges are concentrated into two phase intervals of the sinusoidal voltage supply, when the modulus of the applied voltage difference is high enough and is increasing in time. These two phases of plasma activity are often called Backward Stroke (BD) and Forward Stroke (FD), depending if the high-voltage signal is rising from its minimum to its maximum or decreasing from its maximum to its minimum.
This thesis is motivated by the fact new studies focusing on plasma properties and dynamics are required in order to get better and better aerodynamic results, to understand which parameters mainly affect the actuator performances and to validate numerical models trying to forecast the aerodynamic effects induced by the discharge. This has brought to a scientific collaboration between the Centre of Excellence PlasmaPrometeo of University of Milano-Bicocca and the Aerodynamics and Wind Tunnel Department of the aerospace company Alenia Aermacchi.
During these years I have studied the properties of these discharges by means of electrical and optical diagnostics (mainly Rogowski coils, capacitive probes, a photomultiplier tube and a thermal camera). With some of them a temporal resolution high enough for studying several characteristics of plasma microdischarges has been achieved. This is important because these strokes manifest as series of current and light pulses, lasting tens of nanoseconds and a few nanoseconds respectively. I have first of all carried out a detailed investigation of the properties of these events and of their evolution in space and time in the course of the FD and BD.
It has been pointed out that there are several analogies between the BD and FD, but that not all plasma properties are identical for the two semi-cycles, because of the asymmetrical configuration adopted.
These investigations let think that light and current signals give insights about different microdischarge properties. Light is presumably ascribable to electrons that excite nitrogen immediately after the passage of the ionizing wave that initiates the microdischarge. In contrast, the current signal is due to the movement of charges into the plasma channel and thus reflects the microdischarge temporal evolution, rather than its formation. In the following experiments I have thus focused mainly on the electrical properties of plasma microdicharges, with the aim of better understanding which plasma characteristics are responsible for the ionic wind generation and properties. Several SDBDs with different geometrical configurations and operating parameters have been considered. It has been found that both the discharge and ionic wind characteristics are mainly affected by the dielectric thickness, whereas other properties of the SDBD are less decisive.
These studies are of practical interest because optimizations of SDBD characteristics are still needed for adopting these discharges as plasma actuators for active flow control. In particular, it has been found that at first the speed of the induced wind increases quite linearly with the voltage amplitude, but then this velocity and thus the aerodynamic effects induced by the discharge tend to saturate. This is particularly evident when thin panels are adopted as dielectric barriers.
I thus focused on this topic and I found that an asymmetry in the total charge transported by plasma microdischarges during the backward and forward strokes is favourable for obtaining a ionic wind with a greater velocity, and that the velocity saturation at the highest voltages is associated to a change in discharge regime, which is visible first of all because a pattern of plasma filaments appears superimposed to the more homogeneous plasma. I have thus characterized how this regime transition affects the dynamics of the backward and forward strokes.
Three groups of microdischarges have been identified, depending on their temporal duration, and results let think that they don't contribute equally to the electric wind generation. These studies pave the way to a better understanding of the discharge peculiarities and ionic wind formation, with the aim of understanding if an intrinsic limit exists in plasma actuator potentialities or if new optimization strategies are possible.
Eventually, I proposed to implement the Background Oriented Schlieren (BOS) technique for the visualization and characterization of the airflow induced by the discharge.
The potentialities of this technique have been evaluated in relation to the specifics of the available scientific equipment. The technique has then been proved to be able to visualize density changes induced by plasma. A spatial characterization of the air near the discharge was made in stationary wall jet conditions as well as in the transient period following the discharge ignition when a starting vortex is generated.
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Todoroff, Violaine. "Mesure d’un champ de masse volumique par Background Oriented Schlieren 3D. Étude d’un dispositif expérimental et des méthodes de traitement pour la résolution du problème inverse." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/11303/1/todoroff.pdf.
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Ces travaux consistent à mettre en place un dispositif expérimental BOS3D permettant la reconstruction du champ de masse volumique instantané d'un écoulement ainsi qu'à développer un algorithme de reconstruction permettant une mise à disposition rapide des résultats ainsi qu'une robustesse liée à un nombre faible de points de vue. La démarche a consisté dans un premier temps à développer un algorithme de reconstruction BOS3D applicable à toutes les configurations expérimentales. Pour cela, le problème direct a été reformulé sous forme algébrique et un critère a été défini. Cette formulation ainsi que les équations issues des méthodes d'optimisation nécessaires à la minimisation du critère ont été parallélisés pour permettre une implémentation sur GPU. Cet algorithme a ensuite été testé sur des cas de références issus de calcul numérique afin de vérifier si le champ reconstruit par l'algorithme était en accord avec celui fourni. Dans ce cadre, nous avons développé un outil permettant de simuler numériquement une BOS3D afin d'obtenir les champs de déviation associées aux écoulements numériques. Ces champs de déviation ont ensuite été fournis comme entrée au code et nous ont permis d'étudier la sensibilité de notre algorithme à de nombreux paramètres tels que le bruit sur les données, les erreurs de calibration, la discrétisation du maillage... Ensuite, afin de tester notre code sur des données réelles nous avons mis en place un banc expérimental BOS3D pour la reconstruction du champ de masse volumique instantané. Cela a nécessité l'étude d'un nouveau moyen de mesure, faisant appel à des techniques de calibrage multi-caméras et de nouvelles stratégies d'illumination su fond. Finalement les données issues de l'expérimentation ont été utilisées comme entrée de notre algorithme afin de valider son comportement sur données réelles.
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Todoroff, V. "Mesure d'un champ de masse volumique par Background Oriented Schlieren 3d. Etude d'un dispositif expérimental et des méthodes de traitement pour la résolution du problème inverse." Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2013. http://tel.archives-ouvertes.fr/tel-01020975.
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Cette thèse consiste à mettre en place un dispositif scientifique expérimental BOS3D (Background Oriented Schlieren 3D) à l'ONERA permettant la reconstruction du champ de masse volumique instantané d'un écoulement ainsi qu'à développer un algorithme robuste de reconstruction permettant une mise à disposition rapide des résultats considérant un nombre faible de points de vue. Dans un premier temps, nous avons développé un algorithme de reconstruction BOS3D applicable à toutes les configurations expérimentales. Pour cela, le problème direct, c'est-à-dire l'équation de la déviation des rayons lumineux à travers un milieu d'indice optique non homogène, a été reformulé sous forme algébrique. Un critère régularisé permettant la prise en compte explicite du bruit associé à l'expérimentation a ensuite été défini. Cette formulation ainsi que les équations issues des méthodes d'optimisation nécessaires à la minimisation du critère ont été parallélisées pour permettre une implantation sur GPU. Cet algorithme a ensuite été testé sur des cas de références issus de calcul numérique afin de vérifier si le champ reconstruit par l'algorithme était en accord avec celui fourni. Dans ce cadre, nous avons développé un outil permettant de simuler une BOS3D virtuelle afin d'obtenir les champs de déviation associés aux écoulements numériques. Ces champs de déviation ont ensuite été fournis comme entrée au code de reconstruction et nous ont permis d'étudier la sensibilité de notre algorithme à de nombreux paramètres tels que le bruit sur les données, la discrétisation du maillage, le type de régularisation et le positionnement des caméras. En parallèle de l'étude de la méthode de reconstruction par simulation, nous avons acquis de l'expérience sur la mise en œuvre effective de la mesure BOS dans des installations expérimentales, en participant à plusieurs campagnes d'essais. Cela nous a permis de contribuer à la conception et à la réalisation de bancs de mesures dédiés à la technique BOS. Le principal résultat de ce travail est la réalisation du banc de mesure BOS3D du DMAE, qui permet d'accéder à la reconstruction de champs de masse volumique instantanés. Ces développements expérimentaux nous autorisent finalement à obtenir des reconstructions 3D de champs de masse volumiques moyens et instantanés sur données réelles. De plus, l'analyse du comportement de la méthode numérique BOS3D est proposée en fonction de la nature des écoulements observés et de la configuration d'acquisition.
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Cierpka, Christian. "Zeitaufgelöste PIV-Untersuchungen zur Strömungskontrolle mittels elektromagnetischer Kräfte in schwach leitfähigen Fluiden." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1240481487194-92722.
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Die vorwiegend experimentelle Arbeit befasst sich mit der systematischen Untersuchung von Parametervariationen bei der aktiven Strömungskontrolle mit elektromagnetischen Kräften. An einer angestellten Platte und einem NACA0015-Profil wurde die saugseitige abgelöste Strömung durch das Einbringen einer periodischen wandparallelen Lorentzkraft an der Vorderkante beeinflusst und experimentell mittels zeitaufgelöster Particle Image Velocimetry (PIV) untersucht. Dabei wurde für verschiedene Anstellwinkel und Reynoldszahlen die Frequenz der Anregung, deren Impulseintrag und der zeitliche Kraftverlauf variiert. Strömungsmechanische Untersuchungen experimenteller und numerischer Natur wurden für eine elektrochemische Zelle und den Fall der Elektrolyse an Millieelektroden unter dem Einfluss externer Magnetfelder durchgeführt. Die Übereinstimmung der gemessenen und berechneten Geschwindigkeitsfelder war dabei sehr gut. Entgegen der Annahme, dass im Falle homogener Magnetfelder keine Strömungen induziert werden, konnte nachgewiesen werden, dass durch die lokale Krümmung der elektrischen Feldlinien in Elektrodennähe starke Lorentzkräfte generiert werden. Dies führt zu sehr komplexen Primär-und Sekundärströmungen. Die gleichen Effekte bewirken ebenfalls in der Nähe von Millieelektroden starke Lorentzkräfte in homogenen magnetischen Feldern. Die experimentellen Beobachtungen an Millieelektroden von Leventis et. al (2005), welche zum Beweis der Konzentrationsgradientenkraft herangezogen wurden, konnten alle auf das Wirken lokaler Lorentzkräfte zurückgeführt werden. Der experimentelle Nachweis der Konzentrationsgradientenkraft steht damit weiterhin aus. Zur Messung der Konzentrationen in elektrochemischen Systemen wurde erstmals das Hintergrundschlierenverfahren angewendet. Dieses Verfahren erlaubt die Bestimmung der räumlichen Konzentrationsgradienten mit erheblich weniger messtechnischen Aufwand gegenüber spektroskopischen Methoden und der Schlierentechnik.
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Vallée, Nathalie. "Caractérisation des jets à hautes pressions : étude expérimentale d'injections continues sub-, trans- et super-critiques." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMIR08/document.
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L'étude de l'injection d'un fluide dans des conditions de hautes pressions reste encore aujourd'hui un challenge. Lorsque la pression critique des fluides est dépassée, l'état supercritique est atteint, faisant disparaître la distinction entre liquide et gaz. Pour ces conditions extrêmes, les données expérimentales sont peu nombreuses et nécessitent d'être consolidées. Dans cette étude, un nouveau banc d'essai a été réalisé au laboratoire CORIA dans le but d'étudier des injections non-réactives d'éthane et de propane dans une atmosphère sub- et supercritique d'azote ou d'hélium. Les données ont été collectées à partir de quatre diagnostics optiques : l'ombroscopie, la DBI, la radiographie et la CBOS. Des informations qualitatives sur la topologie des jets et de leur couche de mélange sont apportées. Des mesures quantitatives de longueur de cœur dense, d'angle d'ouverture et de densité sont complétées par une étude phénoménologique à l'aide de la théorie des mélanges binairesStudying a fluid flow under high-pressure conditions through reliable experiments is still nowadays a challenge. When the chamber pressure exceeds the critical pressure of working fluids the supercritical state of matter is reached and the distinction between gas and liquid becomes blurred. For such special conditions, experimental data are scarce and need to be consolidated. In the present study, a new test bench has been designed at CORIA Lab to study the non-reactive injection of ethane and propane into nitrogen or helium under sub- and supercritical conditions. Experimental data are collected from four image-based techniques : shadowgraphy, diffused backlight illumination (DBI), radiography and color background oriented schlieren (CBOS). Qualitative information on topology of the jets and their mixing layer are provided. Quantitative measurements of dense core length, jet spreading angle and density field are supported by a phenomenological study based on binary mixing theory
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Cierpka, Christian. "Zeitaufgelöste PIV-Untersuchungen zur Strömungskontrolle mittels elektromagnetischer Kräfte in schwach leitfähigen Fluiden." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23653.
Full textAbstract:
Die vorwiegend experimentelle Arbeit befasst sich mit der systematischen Untersuchung von Parametervariationen bei der aktiven Strömungskontrolle mit elektromagnetischen Kräften. An einer angestellten Platte und einem NACA0015-Profil wurde die saugseitige abgelöste Strömung durch das Einbringen einer periodischen wandparallelen Lorentzkraft an der Vorderkante beeinflusst und experimentell mittels zeitaufgelöster Particle Image Velocimetry (PIV) untersucht. Dabei wurde für verschiedene Anstellwinkel und Reynoldszahlen die Frequenz der Anregung, deren Impulseintrag und der zeitliche Kraftverlauf variiert. Strömungsmechanische Untersuchungen experimenteller und numerischer Natur wurden für eine elektrochemische Zelle und den Fall der Elektrolyse an Millieelektroden unter dem Einfluss externer Magnetfelder durchgeführt. Die Übereinstimmung der gemessenen und berechneten Geschwindigkeitsfelder war dabei sehr gut. Entgegen der Annahme, dass im Falle homogener Magnetfelder keine Strömungen induziert werden, konnte nachgewiesen werden, dass durch die lokale Krümmung der elektrischen Feldlinien in Elektrodennähe starke Lorentzkräfte generiert werden. Dies führt zu sehr komplexen Primär-und Sekundärströmungen. Die gleichen Effekte bewirken ebenfalls in der Nähe von Millieelektroden starke Lorentzkräfte in homogenen magnetischen Feldern. Die experimentellen Beobachtungen an Millieelektroden von Leventis et. al (2005), welche zum Beweis der Konzentrationsgradientenkraft herangezogen wurden, konnten alle auf das Wirken lokaler Lorentzkräfte zurückgeführt werden. Der experimentelle Nachweis der Konzentrationsgradientenkraft steht damit weiterhin aus. Zur Messung der Konzentrationen in elektrochemischen Systemen wurde erstmals das Hintergrundschlierenverfahren angewendet. Dieses Verfahren erlaubt die Bestimmung der räumlichen Konzentrationsgradienten mit erheblich weniger messtechnischen Aufwand gegenüber spektroskopischen Methoden und der Schlierentechnik.
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King, Timothy. "Optical flow algorithms and background oriented schlieren for a supersonic wind tunnel setup." Thesis, 2018. https://hdl.handle.net/10539/25714.
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University of the Witwatersrand, Johannesburg school of Mechanical, Industrial and Aeronautical Engineering
May 2018The work details a comparison between various GPU accelerated optical flow algorithms that the OpenCV open source computer vision library provides as implemented in a Background Oriented Schlieren (BOS) setup for a supersonic wind tunnel. The chosen test case is the visualisation of supersonic flow (Mach 2.5) over a conical wind tunnel model. The theory for predicting the distortion of the images is developed and used for comparison, as well as a correlation based brute-force block matching algorithm, which is typical of current BOS setups. Additionally, two background images were designed and tested with all algorithms to investigate the interaction between these backgrounds and the various algorithms. The theory behind the optical flow calculations is outlined and discussed in the BOS context and in particular, how it can be used for future background designs. It is also shown that there exists a general compromise between optical flow detail and noise rejection in the processed BOS images and that the more modern algorithms that have been implemented in the OpenCV toolbox generally outperform the traditional correlation based block-matching methods when their accuracy is compared.
MT 2018
Book chapters on the topic "Background Oriented Schlieren"
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Hall, Elise, Jenna Davis, Daniel Guildenbecher, and Brian Thurow. "Plenoptic Background Oriented Schlieren Imaging." In Coded Optical Imaging, 357–67. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-39062-3_19.
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Aguayo Ortiz, A., H. Cardoso Sakamoto, C. Echeverría Arjonilla, D. Porta Zepeda, C. Stern Forgach, and G. Monsivais Galindo. "Calibration of a Background Oriented Schlieren (BOS)." In Recent Advances in Fluid Dynamics with Environmental Applications, 103–14. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-27965-7_8.
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Hatanaka, Kazuaki, and Tsutomu Saito. "Background Oriented Schlieren Method Using Multi-scale Periodic Pattern." In 29th International Symposium on Shock Waves 1, 453–58. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-16835-7_71.
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Kishore, S., M. Pinto, and A. Shukla. "Shock-Structure Interaction Using Background Oriented Schlieren and Digital Image Correlation." In International Digital Imaging Correlation Society, 183–85. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-51439-0_43.
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Richard, H., M. Raffel, M. Rein, J. Kompenhans, and G. E. A. Meier. "Demonstration of the applicability of a Background Oriented Schlieren (BOS) method." In Laser Techniques for Fluid Mechanics, 145–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/978-3-662-08263-8_9.
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Mizukaki, Toshiharu, Hirotaka Tsukada, Kunihiko Wakabayashi, Tomoharu Matsumura, and Yoshio Nakayama. "Quantitative Visualization of Open-Air Explosions by Using Background-Oriented Schlieren with Natural Background." In 28th International Symposium on Shock Waves, 465–70. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-25688-2_71.
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Politz, Christina, Benedikt Over, and Tania Kirmse. "The Application of Background Oriented Schlieren Method to Aircraft Wake Vortex Investigations." In Research Topics in Aerospace, 321–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-34738-2_19.
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Goldhahn, Erik, Olga Alhaj, Florian Herbst, and Jörg Seume. "Quantitative Measurements of Three-Dimensional Density Fields Using the Background Oriented Schlieren Technique." In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 135–44. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-01106-1_14.
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Kameda, M., K. Hayasaka, Y. Tagawa, and T. Liu. "High-Resolution Background-Oriented Schlieren Technique for a Laser-Induced Underwater Shock Wave." In 31st International Symposium on Shock Waves 1, 353–59. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-319-91020-8_40.
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Kiefer, Christian, Dara Feili, Karin Bauer, and Helmut Seidel. "Flow Manipulation by Standing Acoustic Waves and Visualization with Background Oriented Schlieren (BOS)." In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 229–37. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-64519-3_21.
Full textConference papers on the topic "Background Oriented Schlieren"
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Bathel, Brett F., Joshua M. Weisberger, Matthew T. Boyda, and Wayne E. Page. "High-Speed Self-Aligned Focusing Schlieren and Background-Oriented Schlieren with Pulsed Laser Illumination." In Laser Applications to Chemical, Security and Environmental Analysis, LTu3E.2. Washington, D.C.: Optica Publishing Group, 2024. https://doi.org/10.1364/lacsea.2024.ltu3e.2.
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Laser light sources are commonly used in schlieren-based flow visualization techniques that are in development at NASA Langley Research Center. Of particular interest are high-intensity, low coherence sources that allow for high signal-to-noise schlieren imagery to be acquired without the laser speckle that typically occurs as a result of interference. Results from a self-aligned focusing schlieren system developed at NASA Langley and a background-oriented schlieren system are presented to highlight the effectiveness of these sources.
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Léon, Olivier, David Donjat, Pierre Doublet, Adrien Langenais, Aurélien Plyer, and Frédéric Champagnat. "Imaging light ray deviations for reactive supersonic flow sensing and tomography." In Laser Applications to Chemical, Security and Environmental Analysis, LW3E.1. Washington, D.C.: Optica Publishing Group, 2024. https://doi.org/10.1364/lacsea.2024.lw3e.1.
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This work demonstrates the application of high-speed Background Oriented Schlieren for the quantitative analysis of reactive supersonic jets. Tomographic reconstructions of refractive index fields are compared with OH· visualizations and a reactive RANS model.
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Bauknecht, Andre, Friedrich Leopold, Benjamin Ewers, Christian Wolf, and Markus Raffel. "Three-dimensional Reconstruction of Blade Tip Vortices of a BO 105 using a Multi-camera BOS System." In Vertical Flight Society 70th Annual Forum & Technology Display, 1–12. The Vertical Flight Society, 2014. http://dx.doi.org/10.4050/f-0070-2014-9655.
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Noise and structural vibrations in rotorcraft are strongly influenced by interactions between blade tip vortices and the structural components of a helicopter. As a result, the three-dimensional localization of vortices is highly desirable, especially for the case of full-scale helicopters under realistic flight conditions. In the current study, we present results from a flight test with a full-scale BO 105 in an open pit mine. A background-oriented schlieren measurement system consisting of ten cameras was used with a natural background to visualize the vortices of the helicopter under maneuvering flight. Vortex filaments could be visualized and extracted up to a vortex age of 360°. Vortex instability effects were found for several flight conditions. Due to the large test dimensions, an iterative approach based on points on the helicopter fuselage was applied for the camera calibration. Point correspondence between vortex curves in the evaluated images was established by means of epipolar geometry. A three-dimensional reconstruction of the main part of the vortex system was carried out for the first time using triangulation-based stereo-photogrammetry. A quantitative evaluation of the 3D vortex system was carried out, demonstrating the potential of the multi-camera background-oriented schlieren measurement technique for the analysis of blade-vortex interaction effects in rotorcraft.
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Naigle, Shawn, Matthew Frankhouser, James Gregory, and Jeffrey Bons. "Effects of Time-Varying Flow Velocity on Steady Blowing Flow Control for a Pitching Airfoil." In Vertical Flight Society 72nd Annual Forum & Technology Display, 1–12. The Vertical Flight Society, 2016. http://dx.doi.org/10.4050/f-0072-2016-11380.
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This work presents results of an experimental investigation into the effect of time-varying free stream on active flow control of a Sikorsky SSC-A09 airfoil undergoing periodic pitching motion using supersonic, leading edge vortex generator jets. The airfoil was evaluated at reduced pitching frequencies of k=0.026 to k=0.05 at Mach 0.4+0.07cos(ωt) at a mean Reynolds number of 3.0x10⁶. A spanwise row of vortex generator jets located at 10% chord blowing at a jet mass flux ratio (Cq) of 0.001-0.005 demonstrated improvements in both CL and CM hysteresis loops and reductions in negative damping. Initial data indicates that the interaction between VGJ blowing and a time-varying flow delays flow separation during the pitch-up and accelerates flow reattachment during the downstroke. Post-stall shear layer instabilities and airfoil load oscillations are amplified. The VGJ interaction with the shear layer results in an increase in aerodynamic performance determined by the surface pressure taps and illustrated by the use of Background Oriented Schlieren (BOS) as a flow visualization technique.
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Braukmann, Johannes, C. Wolf, and Anthony Gardner. "Application of BOS Velocimetry to Full-scale Helicopter Flight Tests." In Vertical Flight Society 80th Annual Forum & Technology Display, 1–10. The Vertical Flight Society, 2024. http://dx.doi.org/10.4050/f-0080-2024-1060.
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Time-resolved background-oriented schlieren (BOS) data are used to calculate the two-dimensional velocity field in the wake of free-flying full-scale helicopters in ground effect. The calculation is performed based on the density gradient pattern of the helicopter engine exhaust gas passing the BOS field of view. A classical BOS evaluation allows the visualization of density gradients such as vortices and the exhaust plume. The result is the BOS displacement field. Applying the two-dimensional divergence to this data results in a pattern that is constant in shape across multiple BOS images, but convects downstream with the outwash velocity of the helicopter. Using this data as input to a second, timeresolved evaluation, quantitative two-dimensional velocity fields are calculated. Choosing an appropriate strategy for preparing and evaluating the data is critical to reliable velocity estimation. Another important aspect is to distinguish between reliable velocity data and erroneous results in areas of reduced signal intensity due to a lack of thermal structures. The velocity data obtained are compared with an analytical outwash model and constant temperature anemometry data acquired simultaneously with the BOS images. The data show good quantitative agreement in areas of sufficient thermal structures within the field of view.
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Weisberger, Joshua M., and Brett F. Bathel. "Reference-Free, Projection Background Oriented Schlieren." In AIAA AVIATION 2022 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2022. http://dx.doi.org/10.2514/6.2022-3476.
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Luiz Harry Diniz Lemos, Bernardo, Vítor Auguto Andreghetto Bortolin, and GUENTHER Krieger Filho. "BACKGROUND-ORIENTED SCHLIEREN IN A YALE BURNER." In Brazilian Congress of Thermal Sciences and Engineering. ABCM, 2018. http://dx.doi.org/10.26678/abcm.encit2018.cit18-0286.
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Smith, Daniel. "Symmetry-Enforced Coherent Structure Background Oriented Schlieren." In AIAA SCITECH 2023 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2023. http://dx.doi.org/10.2514/6.2023-0007.
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Hartmann, Ulrich, Rafael Adamczuk, and Jorg Seume. "Tomographic Background Oriented Schlieren Applications for Turbomachinery (Invited)." In 53rd AIAA Aerospace Sciences Meeting. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2015. http://dx.doi.org/10.2514/6.2015-1690.
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Li, Zhihao, Xinying Chen, Biao Zhang, Jiatao Meng, Yang Shen, Hang Su, and Chuanlong Xu. "3D Flow Visualization via Background Oriented Schlieren Tomography." In 2022 International Conference on Computing, Communication, Perception and Quantum Technology (CCPQT). IEEE, 2022. http://dx.doi.org/10.1109/ccpqt56151.2022.00020.
Full textReports on the topic "Background Oriented Schlieren"
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Ham, Michael I., Christopher Oshman, Dustin Demoin, Garrett Kenyon, and Harald O. Dogliani. 3D Background Oriented Schlieren Imaging to Detect Aerial Improvised Explosive Devices. Office of Scientific and Technical Information (OSTI), May 2013. http://dx.doi.org/10.2172/1079568.
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Ham, Michael I., Garrett Kenyon, Harald O. Dogliani, Dustin Demoin, and Christopher Oshman. 3D Background Oriented Schlieren Imaging to Detect Aerial Improvised Explosive Devices. Office of Scientific and Technical Information (OSTI), June 2013. http://dx.doi.org/10.2172/1086760.
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