Дисертації: "Jet In Cross-Flow (JICF)"

1

Subramanian, Arunprasath. "Contribution to Aerothermal Study of a Film Cooling Geometric Design using ZnO Phosphorescence Thermography and Numerical Simulations." Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2022. http://www.theses.fr/2022ESMA0006.

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Le refroidissement par film froid des aubes des turbines aéronautiques d’avion est utilisé depuis quelques décennies pour augmenter la température d'entrée de la turbine (TIT) et ainsi augmenter la poussée, et également pour prolonger la durée de vie de l'aube de turbine. Les normes d'émission strictes des polluants encouragent l'amélioration de l'efficacité globale de la turbine et donc l’optimisation du processus de refroidissement par film. C’est une technique par convection forcée dans laquelle un jet froid est injecté à travers des trous discrets à la surface de l'aube de turbine de manière à former une couche d'air frais sur la surface de l'aube protégeant efficacement l'aube des flux à très haute température résultant de la combustion. Ce principe peut être étudié académiquement comme un jet débouchant dans un écoulement transverse. Cet écoulement est très complexe parce que de nombreuses structures cohérentes turbulentes se développent et interagissent les unes avec les autres. L'un des systèmes de tourbillons les plus importants est la paire de tourbillons contra-rotatifs (CRVP) résultant des contraintes de cisaillement qui se développent dans la couche de mélange supérieure entre le jet débouchant et le jet principal. La courbure du jet débouchant le long de la direction du flux transversal intensifie le développement du CRVP qui augmente ainsi le mélange entre les deux écoulements, ce qui réduit l'efficacité du film de refroidissement. Par conséquent, dans cette étude, une organisation spatiale de trous auxiliaires est étudiée expérimentalement et numériquement pour réduire l'intensité de l’influence du CRVP, ce qui contribue finalement à augmenter l'efficacité du refroidissement du film adiabatique. Les trous auxiliaires, placés en amont du trou principal, permettent de réduire l'intensité du CRVP issu du trou principal du fait de la diminution des contraintes de cisaillement subies par le jet issu du trou principal. Dans cette thèse, une méthode numérique basée sur des simulations RANS utilisant le modèle de turbulence k-ω SST a été utilisée pour optimiser l’organisation spatiale des trous auxiliaires et pour avoir une compréhension préliminaire de ces interactions de structures cohérentes. Une étude détaillée de la structure instationnaire de l'écoulement a également été réalisée à l'aide de la simulation aux grandes échelles L.E.S. Pour étudier expérimentalement les champs de température dans le fluide, une métrologie de mesure de température a été spécialement développée : la thermométrie utilisant le rapport d’intensités spectrales d’émission de phosphorescence du ZnO à l’aide d’une seule caméra intensifiée. Cette technique permet la mesure de la température instantanée et moyenne de manière non intrusive. Une analyse détaillée des propriétés d'émission du luminophore ZnO excitée par un laser à 266 nm est décrite. Une procédure d'étalonnage a été développée et testée dans une cavité Rayleigh-Bénard remplie d’eau. Ensuite, cette procédure a été mise en œuvre sur le nouveau banc d'essai BATH pour étudier expérimentalement le film de refroidissement dimensionné par la simulation RANS pour trois taux de soufflage. L'analyse des résultats expérimentaux et numériques aide à identifier les structures cohérentes clés, conduisant à une meilleure compréhension des phénomènes physiques mis en jeu et à appréhender l'augmentation de l'efficacité de refroidissement du film dans le système de trous auxiliaires par rapport à un trou cylindrique simple classique
Film cooling of aircraft gas turbine blades has been in use since a few decades now to improve the Turbine Inlet Temperature (TIT) and to extend the lifetime of the turbine blade. Additionally, stringent emission norms stipulate the improvement of overall efficiency of the gas turbine engine and hence the need to improve film cooling process. Film cooling is a technique where a cold jet is injected through discrete holes on the surface of the turbine blade, so as to form a layer of cool air over the surface of the blade, effectively protecting the blade from high temperature crossflows arising from the combustion chamber. This problem can be viewed as a Jet In Cross-Flow (JICF) phenomena where the interaction of the crossflow with a jet injected perpendicular or at an angle creates a system of vortices. One of the most important vortex systems in this arrangement is the Counter Rotating Vortex Pair arising from the shear forces at the sides of the ejecting jet with the crossflow primarily. The bending of the jet along the direction of the crossflow promotes the CRVP to ingest hot crossflow into the jet stream which reduces the effectiveness of the film cooling system. Hence, in this study, an auxiliary hole system is studied experimentally and numerically to reduce the intensity and the height of the CRVP which eventually helps in an augmented adiabatic film cooling effectiveness. The auxiliary holes placed upstream of the main film cooling hole reduces the intensity of the main hole CRVP due to the reduction in the shear forces experienced by the jet emanating from the main hole. In this thesis numerical analysis through RANS study using k-ω SST turbulence model to have a preliminary understanding of the auxiliary hole system and a detailed understanding of the flow structure using Large Eddy Simulation are performed. The highlight of this work is the development of single camera phosphor thermometry using the spectral intensity ratio method. This technique allows the measurement of the instantaneous and mean flow temperature non-intrusively. A detailed analysis of the emission properties of ZnO phosphor upon excitation by a 266nm laser is described. A calibration procedure for the intensity ratio method is defined and it is tested using a Rayleigh-Bénard natural convection process. This phosphor thermometry procedure with the validated code is implemented on the new BATH test Rig to study film cooling arrangements. Three different configurations are tested for their aero-thermal characteristics at penetration blowing ratio regime. Analysis of the experimental and numerical results help in identifying key vortex structures, leading to the better understanding of reasons for the augmentation of film cooling effectiveness in the auxiliary hole system compared to a classical simple cylindrical hole

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2

Lanitis, Nicolas. "The turbulent structure of the jet in cross-flow." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/246593.

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In this thesis the structure of the jet in cross flow in the far field was investigated experimentally using time-resolved, multi-scale and statistically independent Stereoscopic Particle Image Velocimetry measurements to reveal the mean and instantaneous three-dimensional (3D) structures. All of the measurements were performed in the Counter-rotating Vortex Pair (CVP) plane for a high velocity ratio and jet Reynolds number. Statistical measurements at various downstream locations and velocity ratios are presented. Probability density functions of the streamwise vorticity field showed that each CVP core is instantaneously made of a number of small vortex tubes rather than a single vortex core. The characteristic ‘kidney’ shape was illustrated in the rms velocity profiles and the Reynolds stress profiles exhibited a high level of organisation which showed an evolving shape with downstream distance and persisted well into the far field. Two point spatial correlations pointed to a common structure for all conditions whose mean shape generates the ‘kidney’ shape, as well as evidence of wake structures. Time-resolved measurements were carried out in a moving and stationary frame of reference, converted to 3D measurements via the use of Taylor’s hypothesis. The origin of the ‘kidney’ shape and large degree of spatial order in the far field was found to be a result of an organised ‘train’ of consecutive hairpin, roller and wake structures. Together, these structures provide a physical explanation that reconciles the statistical and instantaneous structure of the CVP.

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3

Ugrina, Sandra. "Experimental analysis and analytical modeling of synthetic jet-cross flow interactions." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6920.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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4

Freedland, Graham. "Investigation of Jet Dynamics in Cross-Flow: Quantifying Volcanic Plume Behavior." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/3314.

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Volcanic eruption columns inject high concentrations of ash into the atmosphere. Some of this ash is carried downwind forming ash clouds in the atmosphere that are hazardous for private and commercial aviation. Current models rely on inputs such as plume height, duration, eruption rate, and meteorological wind fields. Eruption rate is estimated from plume height using relations that depend on the rate of air entrainment into the plume, which is not well quantified. A wind tunnel experiment has been designed to investigate these models by injecting a vertical air jet into a cross-flow. The ratio of the cross-flow and jet velocities is varied to simulate a weak plume, and flow response is measured using particle image velocimetry. The plumes are characterized and flow data relative to the centerline is examined to measure the growth of weak plumes and the entrainment velocity along its trajectory. It was found that cross-flow recirculates behind the jet and entrainment occurs both up and downstream of the jet. Analysis of the generation of turbulence enhanced results by identifying the transition point to bending plume and the growth of the shear layer in a bending plume. This provides information that can be used to improve models of volcanic ash concentration changes in the atmosphere.

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5

Cameron, Andrew William. "Structure of a low-momentum elevated jet in a cross-flow." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/27960.

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An elevated jet in a cross-flow is a free jet issuing orthogonally into a dominant cross-wind from a pipe extending above a ground-induced boundary layer. The present thesis is concerned with jets having low momentum-flux relative to the cross-flow. It presents flow visualization and velocity measurements conducted in a variable-speed, closed-circuit water channel. Four major types of coherent structures were identified: von Karman vortices, a pipe-end vortex, shear-layer vortices, and tendrils. The von Karman vortices are similar to those shed by a finite cylinder with a free end. The pipe-end vortex is a stationary vortex forming immediately downstream of the pipe-end. The shear-layer vortices are formed by the Kelvin-Helmholtz instability in the mixing layer between the cross-flow and the jet. Finally, the tendrils are evolutions of sections of the shear-layer vortices, formed under certain conditions as the latter are stretched by the pipe-end vortex and move downstream. The size of the pipe-end vortex is insensitive to the momentum-flux ratio as long as the latter is less than a critical value. For higher momentum-flux ratios, the pipe-end vortex grows in size and shifts beyond the free-end of the pipe. The Strouhal numbers of the shear-layer vortices and the tendrils increase drastically as the momentum-flux ratio decreases. The shear-layer vortices, marking the jet fluid, move away from the pipe exit upon their generation, then reverse direction as they pass over the pipe-end vortex, while accelerating in the streamwise direction until their velocities approach the cross-flow speed. A vorticity balance for each type of the vortices has been attempted. The von Karman vortices obtain their vorticity from the pressure gradient along the outer surface of the pipe. The pipe-end vortex acquires its vorticity from the shear-layer vortices and generates some vorticity in a pressure gradient on the outer surface of the pipe as well. The shear-layer vortices acquire their vorticity from the cross-flow fluid flowing over the edge of the upstream pipe tip as well as from the vorticity inside the pipe from the jet flow. The vorticity in the tendrils originates in the shear-layer vortices.

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6

Majeski, Adrian Jason. "Size and shape of low momentum jet diffusion flames in cross flow." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0004/MQ59841.pdf.

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7

Lawal, Mohammed Shariff. "Numerical modelling of jet flames in a cross-flow : application to flares." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539693.

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8

Toften, Terje HaÌŠkon. "Effects of free-stream turbulence on a jet in a cross-flow." Thesis, University of Hertfordshire, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241571.

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9

Carrotte, Jonathan F. "The mixing characteristics of dilution jets issuing into a confined cross-flow." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/32627.

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An experimental investigation has been carried out into the mixing of a row of jets injected into a confined cross-flow. Measurements were made on a fully annular test facility, the geometry of the rig simulating that found in the dilution zone of a gas turbine combustion chamber. A small temperature difference of 44°C between the cross-flow and dilution fluid allowed the mixing characteristics to be assessed, with hot jets being injected into a relatively cold cross-flow at a jet to cross-flow momentum flux ratio of 4.0. The investigation concentrated on differences in the mixing of individual dilution jets, as indicated by the regularity of the temperature patterns around the cross-flow annulus. Despite the uniform conditions approaching the dilution holes there were significant differences in the temperature patterns produced by the dilution jets around the annulus.

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10

Fernandez, Jorge Enrique Alvarez. "Calculation of the velocity and temperature fields in a jet in cross-flow." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389408.

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11

Huang, Shengcheng, and 黃晟程. "Effect of ambient turbulence on mixing of a round jet in cross-flow." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/209493.

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12

Nadeau, Patrice. "Study of the mixing with chemical reaction in a cross flow impinging jet aerosol reactor." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0029/NQ64625.pdf.

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13

Boutazakhti, Mohamed. "The effect of jet mixing on the combustion efficiency of a hot, fuel-rich cross-flow." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0015/MQ54105.pdf.

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14

Wu, Zhao. "Direct simulation of a low momentum round jet in channel cross-flow with conjugate heat transfer." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/direct-simulation-of-a-low-momentum-round-jet-in-channel-crossflow-with-conjugate-heat-transfer(53cd2317-917c-44ba-aa70-f4c796fbd6b3).html.

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Results of direct numerical simulations (DNS) of a jet in channel crossflow with conjugate heat transfer are presented. The hot laminar jet issues from a circular exit into the cold channel crossflow with a low jet-to- crossflow velocity ratio of 1/6. The steel channel wall has a finite thickness and its outer side is cooled under Robin type thermal boundary conditions for a realistic external environment, leading to a conjugate heat transfer system. The governing equations are solved by Incompact3d, an open-source code combining the high-order compact scheme and Poisson spectral solver. An internal recycling approach is used to generate the fully turbulent channel ow profile as the inflow conditions. The database is uploaded online for open access (http://dx.doi.org/10.17632/7nx4prgjzz.3). In the fluid domain, four main ow structures are identified: 1) a large recirculation immediately downstream of the jet-exit; 2) a contour-rotating vortex pair originated from the stretching and reorientation of the injection-ow vorticity; 3) a horseshoe vortex generated as a result of the stretching of the vorticity at the jet-exit windward side; and 4) shear layer vortices coming from the lifted and shed crossflow boundary layer vorticity. Proper orthogonal decomposition and dynamic mode decomposition are then used to study the energy and spectrum information of structures. The results show the horseshoe vortex is related to low-frequency modes, while the shear layer vortices are connected to the high-frequency ones. In the conjugate heat transfer problem, the above coherent structures lead to a complex convective and turbulent wall heat transfer pattern around the orifice. Finally, this study evaluates the capabilities of several turbulence models in predicting this type of ow and shows how the DNS database would help test, validate and improve the turbulence models.

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Pinchak, Matthew D. "Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522319737952261.

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16

Recker, Elmar. "Numerical and experimental study of a hydrogen gas turbine combustor using the jet in cross-flow principle." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209733.

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Control of pollutants and emissions has become a major factor in the design of modern combustion systems. The “Liquid Hydrogen Fueled Aircraft - System Analysis” project funded in 2000 by the European Commission can be seen as such an initiative. Within the framework of this project, the Aachen University of Applied Sciences developed experimentally the “Micromix” hydrogen combustion principle and implemented it successfully in the Honeywell APU GTCP 36-300 gas turbine engine. Lowering the reaction temperature, eliminating hot spots from the reaction zone and keeping the time available for the formation of NOx to a minimum are the prime drivers towards NOx reduction. The “Micromix” hydrogen combustion principle meets those requirements by minimizing the flame temperature working at small equivalence ratios, improving the mixing by means of Jets In Cross-Flow and reducing the residence time in adopting a combustor geometry that provides a very large number of very small diffusion flames. In terms of pollutant emissions, compared to the unconverted APU, an essential reduction in emitted NOx was observed, stressing the potential of this innovative burning principle.

The objective of this thesis is to investigate the “Micromix” hydrogen combustion principle with the ultimate goal of an improved prediction during the design process. Due to the complex interrelation of chemical kinetics and flow dynamics, the “Micromixing” was analyzed first. Stereoscopic Particle Image Velocimetry was used to provide insight into the mixing process. A “simplified” set-up, that allowed to investigate the flow characteristics in great detail while retaining the same local characteristics of its “real” counterparts, was considered. The driving vortical structures were identified. To further investigate the physics involved and to extend the experimental results, numerical computations were carried out on the same “simplified” set-up as on a literature test case. In general, a number of physical issues were clarified. In particular, the interaction between the different vortical structures was looked into, and a kinematically consistent vortex model is proposed. After demonstrating the development of the mixing, the “cold flow” study was extended to a single injector. The double backward-facing step injector geometry was addressed experimentally and numerically. At design geometry, the flow appeared to behave single backward-facing like, with respect to the first gradation. In terms of varying step configurations, the flow was seen to be dependent on the periodic perturbation arising from the graded series of backward-facing steps. During the second part of the investigation, the “hot flow” was analyzed. Considering combustor similar operating conditions, a test burner was experimented on an atmospheric test rig. NOx emissions were traced by exhaust gas analysis for different working conditions. Particular flame patterns, such as a regular attached flame as well as lifted flames were observed. In parallel with the experimental work, numerical computations on a pair of opposite injectors, permitted to classify the combustion regime and the main factors involved in the NOx formation. Accordingly, NOx emission enhancing design changes are proposed. Finally, the demanding computational effort, worthy of acceptance for academic purposes, is found not agreeable as future design tool and improvements to speed up the design process are projected.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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El-Okda, Yasser Mohamed. "Jet/Wall Interaction: An Experimental Study with Applications to VSTOL Aircraft Ground Effects." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/32207.

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The flow field of a twin jet impinging on ground plane with and without free-stream and at low jet-height-to-diameter ratios was investigated using the Particle Image Velocimetry (PIV) technique. Detailed, time-averaged flow field data are obtained via the high-resolution and the high-sampling rate instantaneous velocity field that is made available via the PIV technique. A model of twin jet issuing from 0.245m circular plate, with 0.019m jet exit diameter, and with jet span to diameter ratio of 3.0 is placed in a water tunnel with the jets in tandem arrangement with respect to the free-stream. The recently upgraded PIV system, in the ESM department fluid mechanics laboratory at VA-Tech, allowed us to capture instantaneous velocity field images of about 0.076m x 0.076m, at 512(H)x512(V) frame resolution. Sampling rates of 1000 and 1200 fps were employed. Understanding the flow field at lower heights is of crucial significance to the VSTOL aircraft application. Huge jet thrust is required to initiate the take-off operation due to the high lift loss encountered while the airframe is in proximity to the ground. Therefore, jet-height-to-diameter ratios of 2 and 4 were employed in this study. Jet﷓to-free-stream velocity ratios of 0.12, 0.18 and 0.22 were employed in addition to the no-free-stream case. In the current study, only time-averaged flow field properties were considered. These properties were extracted from the available instantaneous velocity field data. In order to provide some details in the time-averaged velocity field, the data were obtained along several planes of interrogation underneath the test model in the vicinity of the twin jet impinging flow. Images were captured in a single plane normal to the free-stream and five planes parallel to the free-stream. A vortex-like flow appears between the main jet and the fountain upwash. This flow is found to experience spiral motion. The direction of such flow spirals is found to be dependent on the jet exit height above the ground, and on the jet-to-free stream, velocity ratios. The flow spirals out towards the vortex flow periphery and upon increasing the free-stream it reverses its direction to be inward spiraling towards the core of the vortex. The flow reversal at certain height of the jet above the ground depends on the free-stream velocity. In our discussion, more emphasis is given to the case of jet-height-to-diameter ratio of two. We also found that the largest turbulent kinetic energy production rate is found to be at the fountain upwash formation zone.
Master of Science

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18

Kolb, Michael [Verfasser]. "Influence of the Injector Geometry on Mixing and Lift-Off of Premixed Jet Flames in Hot Cross Flow / Michael Kolb." München : Verlag Dr. Hut, 2016. http://d-nb.info/1097817857/34.

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19

Feiz, Homayoon. "LES of Multiple Jets in Cross-Flow Using a Coupled Lattice Boltzmann-Navier-Stokes Solver." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14040.

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Three-dimensional large-eddy simulations (LES) of single and multiple jets in cross-flow (JICF) were conducted using the 19-bit Lattice Boltzmann Equation (LBE) method coupled with a conventional Navier-Stokes (NS) finite-volume scheme. In this coupled LBE-NS approach, the LBE-LES was employed to simulate the flow inside jet nozzles, while the NS-LES was used to simulate the cross-flow. The key application area was to study the micro-blowing technique (MBT) for drag control similar to recent experiments at NASA/GRC. A single jet in the cross-flow case was used for validation purposes, and results were compared with experimental data and full LBE-LES simulation. Good agreement with data was obtained. Transient analysis of flow structures was performed to investigate the contribution of flow structures to the counter-rotating vortex pair (CRVP) formation. It was found that both spanwise roller (at the lee side of the jet) and streamwise vortices (at the jet-side) contribute to the generation of the CRVP. Span-wise roller at the corner of the jet experiences high spanwise vortex compression as well as high streamwise vortex stretch. As a result, they get realigned, mix with the jet-side streamwise vortices, and eventually generate the CRVP. Furthermore, acoustic pulses were used to test the proper information exchange from the LBE domain to the NS domain, and vice-versa. Subsequently, MBT over a flat plate with porosity of 25 percent was simulated using nine jets in a compressible cross-flow at a Mach number of 0.4. Three cases with injection ratios of 0.003, 0.02 and 0.07 were conducted to investigate how the blowing rate impacts skin friction. It is shown that MBT suppressed the near-wall vortices and reduced the skin friction by up to 50 percent. This is in good agreement with experimental data.

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KISHORE, ARAVIND. "Numerical Modeling of Pollutant Dispersal from Watercraft Exhaust Systems." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1212173987.

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Almutlaq, Ahmed N. "Density-based unstructured simulations of gas-turbine combustor flows." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/13892.

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The goal of the present work was to identify and implement modifications to a density-based unstructured RANS CFD algorithm, as typically used in turbomachinery flows (represented here via the RoIIs-Royce 'Hydra' code), for application to Iow Mach number gas-turbine combustor flows. The basic algorithm was modified to make it suitable for combustor relevant problems. Fixed velocity and centreline boundary conditions were added using a characteristic based method. Conserved scalar mean and variance transport equations were introduced to predict scalar mixing in reacting flows. Finally, a flarnelet thermochemistry model for turbulent non-premixed combustion with an assumed shape pdf for turbulence-chemistry interaction was incorporated. A method was identified whereby the temperature/ density provided by the combustion model was coupled directly back into the momentum equations rather than from the energy equation. Three different test cases were used to validate the numerical capabilities of the modified code, for isothermal and reacting flows on different grid types. The first case was the jet in confined cross flow associated with combustor liner-dilution jetcore flow interaction. The second was the swirling flow through a multi-stream swirler. These cases represent the main aerodynamic features of combustor primary zones. The third case was a methane-fueled coaxial jet combustor to assess the combustion model implementation. This study revealed that, via appropriate modifications, an unstructured density-based approach can be utilised to simulate combustor flows. It also demonstrated that unstructured meshes employing nonhexahedral elements were inefficient at accurate capture of flow processes in regions combining rapid mixing and strong convection at angles to cell edges. The final version of the algorithm demonstrated that low Mach RANS reacting flow simulations, commonly performed using a pressure-based approach, can successfully be reproduced using a density-based approach.

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Duda, Benjamin Markus. "Étude et analyse numérique d’un jet chaud débouchant dans un écoulement transverse en utilisant des simulations aux échelles résolues." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0021/document.

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Des méthodes numériques sont présentées qui permettent la simulation de jets chauds débouchants dans un écoulement transverse aux grands nombres de Reynolds et aux rapports des vitesses faibles. Différentes approches pour la modélisation de turbulence, c'est-à-dire URANS, SAS, DDES et ELES, sont validées par comparaison à des données expérimentales pour une configuration générique, soulignant la nécessité de résoudre les différentes échelles turbulentes pour une prévision correcte du mélange thermique. L'analyse de la solution instationnaire permet l'identification de processus dynamiques intrinsèques ainsi que des phénomènes de mélange et l'application de l'analyse en composantes principales révèle l'ondulation latérale du sillage de jet. Du fait du caractère multi-échelles qui se manifeste dans la simulation d'un jet débouchant sur une configuration avion, l'approche séquentielle basée sur le modèle SAS est mise en place. Comme les résultats pour la sortie d'un système de dégivrage de nacelle sont en bon accord avec les données d'essai en vol, cette approche est finalement appliquée à la sortie complexe d'un système de pre-cooler, mettant en valeur sa capacité à être appliquée dans un processus industriel
Numerical methods for the simulation of hot jets in cross flow at high Reynolds numbers and small momentum ratios are presented. Different turbulence modeling strategies, i.e. URANS, SAS, DDES and ELES, are validated against experimental data on a generic configuration, highlighting the necessity of scale-resolution for a correct prediction ofthermal mixing. The analysis of transient flow simulations allows the identification of inherent flow dynamics as well as mixing phenomena and the application of the Proper Orthogonal Decomposition revealed the lateral wake meandering as being one of them. Due to the multi-scale problem which arises when simulating jets in cross flow on real aircraft configurations, the sequential approach based on the SAS turbulence model is introduced. As results for the exhaust of a nacelle anti-icing system comprising multiple jets in cross flow agree well with flight test data, the approach is applied in a last step to the complex exhaust of a pre-cooling system, emphasizing the capabilities of this methodology in an industrial environment

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23

Bocquet, Sébastien. "Modélisation de paroi et injection de turbulence pariétale pour la Simulation des Grandes Echelles des écoulements aérothermiques." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/10307/1/bocquet.pdf.

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Анотація:

Lors du développement d’un nouvel avion, l’estimation des échanges d’énergie entre l’air ambiant et les parois est une donnée cruciale pour la conception aérothermique. Cette conception repose de plus en plus sur des simulations numériques mais certains phénomènes d’aérothermique externe, comme le jet débouchant du système de dégivrage des nacelles moteur, montrent les limites des modèles RANS classiques. La simulation des grandes échelles (LES) se révèle bien adaptée à ce type de phénomène mais se heurte à un coût de calcul extrêmement élevé pour ces écoulements pariétaux à très grand nombre de Reynolds. Pour lever cette limitation, cette thèse propose l’étude de deux briques fondamentales : la LES avec loi de paroi (WMLES) conjuguée à l’injection d’une couche limite turbulente à l’entrée du domaine. Pour une meilleure compréhension et une utilisation fiable de l’approche loi de paroi, on se concentre tout d’abord sur les sources d’erreur qui lui sont associées. Après les avoir identifiées, on propose une correction de l’erreur de sous-maille ainsi qu’une loi de paroi adaptée aux écoulements compressibles. Grâce à ces deux éléments, on obtient une estimation correcte du flux de chaleur pariétal sur des simulations WMLES de canal plan supersonique sur parois froides. Puis, pour préparer la transition vers des applications plus industrielles, on introduit un schéma numérique plus dissipatif ce qui nous permet d’étudier l’influence de la méthode numérique sur l’approche loi de paroi. Dans une seconde partie dédiée à l’injection de couche limite pour la WMLES, on sélectionne une méthode basée sur l’injection de perturbations combinée à un terme de contrôle volumique. On montre que des simulations WMLES utilisant cette méthode d’injection permettent d’établir une couche limite turbulente réaliste à une courte distance en aval du plan d’entrée, à la fois sur une plaque plane mais également sur un écoulement de jet débouchant à la géométrie plus complexe, représentative d’un cas avion.

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24

Borner, Sebastian. "Optimization and testing of a low NOx hydrogen fuelled gas turbine." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209471.

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A lot of research effort is spent worldwide in order to reduce the environmental impact of the transportation and power generation sector. To minimize the environmental pollution the role of hydrogen fuelled gas turbines is intensively discussed in several research scenarios, like the IGCC-technology or the application of hydrogen as large scale storage for renewable energy sources. The adaptation of the applied gas turbine combustion chamber technology and control technology is mandatory for a stable and secure low NOx operation of a hydrogen fuelled gas turbine.

The micromix combustion principle was invented at Aachen University of Applied Sciences and achieves a significant reduction of the NOx-emissions by the application of multi miniaturized diffusion-type flamelets. Based on the research experiences, gained during the two European hydrogen research programs EQHHPP and Cryoplane at Aachen University of Applied Sciences, the intention of this thesis was to continue the scientific research work on low NOx hydrogen fuelled gas turbines. This included the experimental characterization of the micromix combustion principle, the design of an improved combustion chamber, based on the micromix combustion principle, for industrial gas turbine applications and the improvement of the gas turbine’s control and metering technology.

The experimental characterization of the micromix combustion principle investigated the impact of several key parameters, which influence the formation of the NOx-emissions, and allows therefore the definition of boundary conditions and design laws, in which a low NOx operation of the micromix combustion principle is practicable. In addition the ability of the micromix combustion principle to operate at elevated energy densities up to 15 MW/(m2bar) was successfully demonstrated. The improved combustion chamber design concept includes the experiences gained during the experimental characterization and covers the industrial needs regarding scalability and manufacturability.

The optimization and testing is done with an Auxiliary Power Unit GTCP 36-300. The original kerosene fuelled gas turbine was modified for the hydrogen application. Therefore several hardware and software modifications were realized. The improved gas turbine’s control and metering technology enables stable and comparable operational characteristics as in kerosene reference. An improved hydrogen metering unit, which is controlled by the industrial Versatile Engine Control Box, was successfully implemented.

The combination of the micromix combustion technology and of the optimized control and metering technology allows a stable, secure and low NOx hydrogen fuelled gas turbine operation.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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25

Wang, S. M., and 王孝民. "Flow structure and mixing characteristics of combusting jet in cross-flow." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/82013928035992923485.

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碩士
國立臺灣科技大學
機械工程研究所
83
The characteristic flame modes and velocity structures of the combusting gas jet in cross air flow were experimentally investigated. The flame configurations in the stability domain of the wake-stablized flame were classified into six characteristic modes: down washed flame, flashing flame, developing flame, dual flame, flickering flame, and pre-blow- off flame. The flame and flow fields shone by the laser light sheet delineated the correlation between the positions of fuel and flames. The complex behavior of the coherent structure was found to heavily depend on jet-to-wind momentum flux ratio. A two-component laser-Dopper velocimeter was employed to measure the velocity structure. The stream line, jet trajectory, vorticity field, turbulence intensity, and shear stress field of this class of flames were substantially analyzed and discussed.

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26

Hsuan, Chen，Yih, and 鄭憶萱. "Numerical simulation of buoyant jet in density - stratified cross flow." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/83338994239376932705.

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27

Juan, Wei-cheng, and 阮煒程. "On the Diffusion of a Round Jet in a Cross Flow." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/63400523747190951853.

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Анотація:

碩士
國立臺灣科技大學
機械工程系
93
Flow patterns and variations of pollutant concentration induced by a jet coming from a vertical round tube in a crossflow are numerically simulated in this study.Various flow patterns with respect to the momentum ratio R of jet to cross wind are investigated. There are four characteristic modes in the predicted flows, i.e.downwash, crossflow-dominated, transition and jet-dominated. A hovering vortex is observed in the vicinity of the exit of the round tube when R is less than 0.2. It shrinks due to a growing vertical jet when R increases. Furthermore, it is found that R dominates the concentration variation in the jet via the analysis of concentration fields. Pollutants are downwashed when R is less than 0.5, but pollutants are only found in the region above the exit of the round tube. A pair of counter-rotating vortices are found in the cross section of a jet in a cross flow. Those vortices induce the entrainment effect which mixes up fluids in jet and cross flow. It becomes the main mechanism of pollutant diffusion in the flow.

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28

Wun-Bin, Liu, and 劉文彬. "3-D numerical simulations of square tube jet in cross flow." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/3k7s58.

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碩士
國立臺灣科技大學
機械工程系
94
This study aims to investigate a jet coming from a square tube in a still environment or in a cross wind using an in-house numerical model. The cross sectional flow structure of a square jet in a still environment is similar to a steady radioactive shape. When the jet interacts with a cross wind, the flow structures can be categorized into four modes according to various momentum ratio of jet to cross flow $R$, i.e. downwash, cross wind dominated, transition, and jet dominated modes. This study reveals evolution of wakes behind the jet and the square tube at Re = 1,000 and 2,074. The downwash mode shows that jet momentum is not strong enough, so the jet is downwashed along the tube. In the cross flow dominated mode, a vortex behind the jet is found. In the transition mode, the jet begins to swing when traveling downstream. This phenomenon disappears in the jet dominated mode. The Counter-rotating Vortex Pair (CVP) is clearly shown in the cross sectional structure of the jet in a cross flow. Ambient fluids are entrained into the jet due to CVP. The numerical results also provide variations of jet height, angle of jet, shear stress and vorticity with respect to varying R.

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29

Yang, Ming Zhe, and 楊明哲. "Structure and characteristics of a never-lift combusting jet in cross-flow." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/44759281205735904006.

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30

Min, Change Chin, and 張俊民. "The Stability and Visualized Flame and Flow Structure of a Combustion Jet in a Cross Flow." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/77594024524133221795.

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Анотація:

碩士
國立臺灣科技大學
工程技術研究所
81
The blow-off stability and flame behavior of a combusting propane gas jet issuing from a well contoured burner per pendicularly to a cross air stream in a wind tunnel test section is studied experimentally. Across a certain range of Reynolds number of the wind stream the critical fuel jet Reynolds number which causes the flame blow off is found declined abruptly and hence categorizes the stability domain into three regimes: subcritical, critical,and supercritical regimes. The flame configurations in each stability regime are identified as few characteristic modes: circulating flame, flashing flame, developing flame, dual-flame, flickering flame, and the flame prior to blow-off. The schlieren photographs are presented to discuss the effects of the flow structures on the general behaviour of the flames in each characteristic mode and on the flame stability characteristics. The different flow structures correspond to the different appearance of the characteristic flame modes. The unsteady triggering of the vortex structures in the shear-layer keeps in phase with the flickering of the flames and hence dominates the process of the mixing in the down-stream area. The bisector of the eddy straveling avenue reasonably depicts the near-burner trajectory of the partially detached flame in cross flow.

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31

Ke, Zhao-Tang, and 柯照堂. "Numerical investigation on the near-exit flow characteristics of A ring jet with a cross flow." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/74671768039340120156.

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Анотація:

碩士
北台灣科學技術學院
機電整合研究所
97
This article is based on experimental observation and numerical simulation methods to investigate the ring-side jet vents like in the field in the cross-wind field under the effect of structural changes and the like. Cross-wind from an open loop wind tunnel provided by the high-pressure jet of air through the rectifier into a vertical wind tunnel layer, and the use of laser-light sheet visualization of the smoke flow field to obtain the flow field pattern.This study is aimed at the analysis and discussion on the flow structures near the wake region numerically as the fluids of annular jet are discharged in a cross flow. By altering the velocities of the crosswind and annular jet, the flow patterns present three flow modes of single-bubble, dual-bubble and symmetric-bubble. Flow with different crosswind conditions is simulated to make sure that the velocity ratio R is the factor to decide the flow mode. The flow structure and characteristic of the near wake will be different with the change of the velocity ratio. Only a single bubble exists behind the bluff-body in the single-bubble mode when the velocity ratio is less. The right bubble and a four-way saddle point appear in the dual-bubble mode when the velocity ratio increases to be above 1.75. But, two bubbles of two sides are not symmetric.

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32

Sheu, Dar Woei, and 許達偉. "The Experimental Investigation of Two-Dimensinoal Single Jet in a Uniform Cross Flow." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/58180996582710508351.

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33

Lee, Wen Cheng, and 李文正. "The Numerical Simulation of Two-Dimensinoal Single Jet in a Uniform Cross Flow." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/49543230858147453931.

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34

Stander, Arjan. "The effects of pulsing and blowing ratio on a 45�� inclined jet in cross flow." Thesis, 2002. http://hdl.handle.net/1957/31689.

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The effect of jet flow pulsing and blowing ratio on a jet in cross flow has been investigated. Preliminary jet flow studies were performed without cross flow and an extensive study of jet with cross flow was done for a total of nine test cases. The effect of velocities ratios of 0.85 and 3.4, as well as pulsing the jet flow at 20Hz, was investigated in the near and far field of the jet. A comparison between the jet in cross flow and an inclined cylinder in cross flow was also performed. Hot film measurements were taken within a grid of the flow field in the jet symmetry plane and out of the symmetry plane. Instantaneous velocities were generated at each location and mean velocity, RMS values, Reynolds stresses and mean vorticity were calculated and compared for each case. The higher velocity ratio case (VR=3.4) caused the jet flow to lift up from the wall penetrating into the cross flow compared to the lower velocity ratio case (VR=0.85) where the jet fluid remained attached to the wall and no lift off was observed. The higher velocity ratio case resulted in increased mean velocities, RMS values, Reynolds stresses and mean vorticity throughout the flow field compared to the low velocity ratio case. Secondary turbulent structures were discovered in the wake region of the inclined cylinder. Similar structures were absent in the downstream flow region during the jet in cross flow experiments. There was no significant effect on the jet trajectory as a result of jet pulsing. For both velocity ratio cases the jet trajectory remained similar to the steady cases. Jet pulsing increased the instantaneous velocity RMS levels and Reynolds stresses in the near field of the jet, but did not seem to affect the RMS levels and Reynolds stresses beyond x/d=4. Jet pulsing had a significant effect on the distribution of spectral energy. Distinct energy peaks are generated at the pulsing frequency and its harmonics. The distinct spectral peaks were largest close to the jet exit and within the jet flow, but were detectable throughout the entire flow field.
Graduation date: 2003

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35

Tsai, Bo-chin, and 蔡博欽. "An experimental study of a round tube jet in a stationary environment and a cross-flow environment." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/827w6q.

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碩士
國立臺灣科技大學
機械工程系
100
The research studies the features of round tube jets in a stationary environment and the trajectory analysis of round tube jets in a cross-flow environment. The experiments were carried out in a vertical closed-loop water tunnel. Flow structures were observed by using flow visualization and Particle Image Velocimetry(P.I.V.) techniques respectively. For round tube jets in a stationary environment, the characteristics of the flow rate and the maximum axial velocity are different for the round tube jets having different Reynolds numbers. Particle Image Velocimetry uses two interrogation cells to analyze captured images. A finer cell has results approaching to the theoretical model. Experimental results show that, the vortex ring formation changes the flow rate and the velocity field of the jet significantly. The velocity profile of the jet is closer to that of Schlichting theory after the vortex ring formation. For the trajectory analysis results of round tube jets in a cross-flow environment, three different trajectories determined by streamline, velocity and vorticity are notably different when the velocity ratio is less than 3 or larger than 9. This research uses streamline trajectory to analyze a round tube jet in a cross-flow environment. Experimental data are analyzed under two specific conditions of the same velocity ratio and the same cross-flow velocity. Experimental results show that Reynolds number is an important index for jet trajectory for these two conditions. When the Reynolds number of the jet is in the transition region, the trajectory of the jet shows some changes, especially the maximum axial distance which the jet can reach. When the Reynolds number is in the turbulent region, the jet trajectory is similar to those reported in the previous literature.

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36

Rashad, Muhammad Aqeel [Verfasser]. "CFD simulation of jet and vortex actuators (JaVA) with and without cross flow boundary layer / by Muhammad Aqeel Rashad." 2010. http://d-nb.info/100838013X/34.

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37

Rickmers, Peter [Verfasser]. "Experimental investigation of the spray autoignition of n-heptane in a jet in cross flow configuration and comparison to single droplet ignition simulations / von Peter Rickmers." 2010. http://d-nb.info/1008216763/34.

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38

Almeida, Celso Oliveira. "Simulação CFD de jatos em espaços confinados." Master's thesis, 2013. http://hdl.handle.net/1822/28172.

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Dissertação de mestrado integrado em Engenharia Mecânica
A presente tese tem por objetivo o estudo da interação de um jato num escoamento livre. Com este objetivo efetuou-se a modelação do escoamento usando o software de Computação em Dinâmica dos Fluidos – CFD – ANSYS FLUENT. Este baseia-se na utilização da técnica de volumes finitos para a solução das equações de conservação de um fluido: massa, momentum e energia. Neste estudo foram consideradas três situações: interação de um jato com um fluido em repouso; interação de um jato com um fluxo perpendicular e a interação de 13 jatos com um fluxo perpendicular. Neste estudo foram avaliados vários modelos de turbulência e a influência de gradientes térmicos entre os dois fluxos. Os dados obtidos foram comparados com resultados experimentais obtidos por Nunes (2003) num túnel de vento subsónico. De entre os vários modelos de turbulência o k-e mostrou ser o mais adequado. A convergência da solução exigiu um elevado refinamento da malha na região de interação dos fluxos. Os resultados mostram que a injeção cruzada de caudais relativamente pequenos pode provocar o estabelecimento de extensas regiões de interação com a corrente principal, acompanhadas da criação de vórtices, os quais contribuem, eficazmente, para a rápida mistura das duas correntes. A simulação CFD de temperatura para um jato mostrou que a 30D ocorre um alargamento da pluma que abrange quase metade da secção transversal e uma boa homogeneização, então a 120D ocorre o alargamento da pluma que abrange quase a totalidade da secção transversal e uma óptima homogeneização. A simulação CFD de temperatura para 13 jatos mostrou que já a partir de 30D, ocorre um alargamento toroidal da pluma e uma boa homogeneização. Verifica-se que quer para 1 e 13 jatos, quanto menor a temperatura do jato, mais alta é a posição da pluma a 120D a jusante da injeção, tal situação deve-se ao fenómeno da conveção natural.
This thesis aims to study the interaction of a jet in a free-flowing. With this aim was carried out by modeling the flow field using the software on Computational Fluid Dynamics - CFD – ANSYS FLUENT. This is based on the use of the finite volume technique for solving the conservation equations of fluid: mass, momentum and energy. In this study, three cases were considered: interaction with a jet of a fluid at rest; interaction of a single jet with a cross-flow and the interaction of 13 jets in cross flow. In this study, various turbulence models and the influence of thermal gradients between the two streams were evaluated. The data obtained were compared with experimental results obtained by Nunes (2003) in a subsonic wind tunnel. Amongst the various turbulence models the k-e proved to be the most suitable. The convergence of the solution required a high mesh refinement in the region of interaction flows. The results show that the injection of relatively small cross-flow rates can cause the establishment of large regions of interaction with the main flux, accompanied by the creation of eddies, which contribute effectively to rapid mixing of the two streams. A CFD simulation of temperature showed that a jet 30D is an extension of the plume covering almost half of the cross section and a good homogeneity, then the extension of the plume 120D which covers almost the entire cross section and an optimum mixing occurs. The CFD simulation temperature to 13 jets showed that a toroidal extension of the plume and a good homogenization starting 30D downstream of the injection point, occurs.

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39

Joarder, Ratan. "Demonstration Of Supersonic Combustion In A Combustion Driven Shock-Tunnel." Thesis, 2009. http://hdl.handle.net/2005/1005.

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For flights beyond Mach 6 ramjets are inefficient engines due to huge total pressure loss in the normal shock systems, combustion conditions that lose a large fraction of the available chemical energy due to dissociation and high structural loads. However if the flow remains supersonic inside the combustion chamber, the above problems could be alleviated and here the concept of SCRAMJET(supersonic combustion ramjet) comes into existence. The scramjets could reduce launching cost of satellites by carrying only fuel and ingesting oxygen from atmospheric air. Further applications could involve defense and transcontinental hypersonic transport. In the current study an effort is made to achieve supersonic combustion in a ground based short duration test facility(combustion driven shock-tunnel), which in addition to flight Mach number can simulate flight Reynolds number as well. In this study a simple method of injection i.e. wall injection of the fuel into the combustion chamber is used. The work starts with threedimensional numerical simulation of a non-reacting gas(air) injection into a hypersonic cross-flow of air to determine the conditions in which air penetrates reasonably well into the cross-flow. Care is taken so that the process does not induce huge pressure loss due to the bow shock which appears in front of the jet column. The code is developed in-house and parallelized using OpenMp model. This is followed by experiments on air injection into a hypersonic cross-flow of air in a conventional shock-tunnel HST2 existing in IISc. The most tricky part is synchronization of injection with start of test-flow in such a short duration(test time 1 millisecond) facility. Next part focuses on numerical simulations to determine the free-stream conditions, mainly the temperature and pressure of air, so that combustion takes place when hydrogen is injected into a supersonic cross-flow of air. The simulations are two-dimensional and includes species conservation equations and source terms due to chemical reactions in addition to the Navier-Stokes equations. This code is also built in-house and parallelized because of more number of operations with the inclusion of species conservation equations and chemical non-equilibrium. However, the predicted conditions were not achievable by HST2 due to low stagnation conditions of HST2. Therefore, a new shock-tunnel which could produce the required conditions is built. The new tunnel is a combustion driven shock-tunnel in which the driver gas is at higher temperature than conventional shock-tunnel. The driver gas is basically a mixture of hydrogen, oxygen and helium at a mole ratio of 2:1:10 initially. The mixture is ignited by spark plugs and the hydrogen and oxygen reacts releasing heat. The heat released raises the temperature of the mixture which is now predominantly helium and small fractions of water vapour and some radicals. The composition of the driver gas and initial pressure are determined through numerical simulations. Experiments follow in the new tunnel on hydrogen injection into a region of supersonic cross-flow between two parallel plates with a wedge attached to the bottom plate. The wedge reduces the hypersonic free-stream to Mach 2. A high-speed camera monitors the flow domain around injection point and sharp rise in luminosity is observed. To ascertain whether the luminosity is due to combustion or not, two more driven gases namely nitrogen and oxygen-rich air are used and the luminosity is compared. In the first case, the free-stream contains no oxygen and luminosity is not observed whereas in the second case higher luminosity than air driver case is visible. Additionally heat-transfer rates are measured at the downstream end of the model and at a height midway between the plates. Similar trend is observed in the relative heat-transfer rates. Wall static pressure at a location downstream of injection port is also measured and compared with numerical simulations. Results of numerical simulations which are carried out at the same conditions as of experiments confirm combustion at supersonic speed. Experiments and numerical simulations show presence of supersonic combustion in the setup. However, further study is necessary to optimize the parameters so that thrust force could be generated efficiently.

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Дисертації з теми "Jet In Cross-Flow (JICF)"

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