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Добірка наукової літератури з теми "Laminar breakdown"

Автор: Grafiati

Опубліковано: 5 жовтня 2024

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Статті в журналах з теми "Laminar breakdown"

Li, Ning, and Qi Hong Zeng. "Direct Numerical Simulation on Transition of an Incompressible Boundary Layer on a Flat Plate." Applied Mechanics and Materials 268-270 (December 2012): 1143–47. http://dx.doi.org/10.4028/www.scientific.net/amm.268-270.1143.

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Direct Numerical Simulation(DNS) was carried out for laminar-turbulent transition of an incompressible boundary layer on a flat plate based on disturbance Navier-Stokes(N-S) equation in spatial mode with Massage Passing Interface(MPI) technology. Study on breakdown mechanism of laminar-turbulent transition was carried on. The effect of mean flow distortion on the process of breakdown in laminar-turbulent transition was investigated. Results indicate that change of instability characteristic of mean flow profile plays a key role during process of breakdown.

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Kadyirov, A. I., and B. R. Abaydullin. "Vortex Breakdown under Laminar Flow of Pseudoplastic Fluid." Journal of Physics: Conference Series 899 (September 2017): 022009. http://dx.doi.org/10.1088/1742-6596/899/2/022009.

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Zhou, Teng, Zaijie Liu, Yuhan Lu, Ying Wang, and Chao Yan. "Direct numerical simulation of complete transition to turbulence via first- and second-mode oblique breakdown at a high-speed boundary layer." Physics of Fluids 34, no. 7 (July 2022): 074101. http://dx.doi.org/10.1063/5.0094069.

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Complete transition to turbulence via first- and second-mode oblique breakdown in a high-speed boundary layer at Mach 4.5 is studied by direct numerical simulations (DNS) and linear stability theory (LST). The initial frequency and spanwise wavenumbers for both types of oblique breakdown are determined from LST. Then, DNS is employed to study the main features of the two oblique breakdown types in detail, which has rarely been discussed in previous studies. This includes the main flow structures and evolution of various modes during the linear, nonlinear, and breakdown stages, and both different and similar features for the two oblique breakdown types are summarized. Compared with only one type of low-speed streak existing for first-mode oblique breakdown, two types occur in the second-mode oblique breakdown, and the generation mechanism, evolution process, and role of the low-speed streaks are studied. Subsequently, the generation mechanism of both the heat transfer and skin-friction overshoot during both oblique breakdowns is illustrated with emphasis on the heat transfer overshoot for the second mode, which occurs at the laminar stage. Finally, both types of oblique breakdown are the likely path to a fully developed turbulent flow, although the unstable region for the second-mode oblique waves is short and for the first-mode oblique waves is amplified slowly.

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Seifi, Zeinab, Mehrdad Raisee, and Michel J. Cervantes. "Optimal flow control of vortex breakdown in a laminar swirling flow." Journal of Physics: Conference Series 2707, no. 1 (February 1, 2024): 012129. http://dx.doi.org/10.1088/1742-6596/2707/1/012129.

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Abstract In highly swirling flows, such as hydraulic turbines operating under part-load (PL) conditions, vortex breakdown occurs and performance is impaired. Consequently, it is imperative that mitigation measures are taken. In the present study, a laminar swirling flow with a vortex breakdown at a Reynolds number of 180 is investigated. At the inlet, a swirling velocity profile with a swirl number of 1.095 is set. A stability analysis is conducted to identify unstable modes based on the assumption that vortex breakdown is a global instability. The results indicate that spiral modes with wave number 1 are unstable. An optimal flow control method based on the Adjoint method is then utilized to mitigate vortex breakdown. In the present study, the control method targets vorticity using a minimization algorithm. Control variables include radial and axial body forces. According to the results, the method was effective in mitigating vortex breakdown. A stability analysis conducted during the control process revealed that as the vorticity decreased, the growth-rate of the eigenvalue decreased, indicating that the flow is stabilized.

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Kachanov, Yu S. "On the resonant nature of the breakdown of a laminar boundary layer." Journal of Fluid Mechanics 184 (November 1987): 43–74. http://dx.doi.org/10.1017/s0022112087002805.

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The first part of this paper (§2) briefly reviews the history of the idea of the resonant nature of laminar-boundary-layer breakdown. In the second part a new wave-resonance concept of the breakdown mechanism is proposed. The existing experimental data on the laminar boundary layer (and plane channel flow) breakdown are analysed from the viewpoint of this concept and are compared with the well-known local high-frequency secondary-instability concept. The results testify to the correctness of the proposed wave-resonant concept for the initial stages of breakdown, in particular for the K-regime of transition up to the spike formation and its doubling.Within the framework of the wave-resonance concept, before constructing the corresponding theory, many important features of the disturbance development can be qualitatively explained and understood. Concerning the understanding of the spike appearance, the wave-resonance concept complements the local high-frequency secondary-instability one and represents by itself a new fruitful viewpoint on this phenomenon. The development of the wave-resonance concept and its application to the analysis of numerical and physical experiments, together with the construction on this basis of the corresponding theory, can give an essential impetus towards the better understanding of the breakdown nature.

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Bottaro, Alessandro, Inge L. Ryhming, Marc B. Wehrli, Franz S. Rys, and Paul Rys. "Laminar swirling flow and vortex breakdown in a pipe." Computer Methods in Applied Mechanics and Engineering 89, no. 1-3 (August 1991): 41–57. http://dx.doi.org/10.1016/0045-7825(91)90036-6.

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Ozdemir, Celalettin E., Tian-Jian Hsu, and S. Balachandar. "Direct numerical simulations of instability and boundary layer turbulence under a solitary wave." Journal of Fluid Mechanics 731 (August 28, 2013): 545–78. http://dx.doi.org/10.1017/jfm.2013.361.

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AbstractA significant amount of research effort has been made to understand the boundary layer instability and the generation and evolution of turbulence subject to periodic/oscillatory flows. However, little is known about bottom boundary layers driven by highly transient and intermittent free-stream flow forcing, such as solitary wave motion. To better understand the nature of the instability mechanisms and turbulent flow characteristics subject to solitary wave motion, a large number of direct numerical simulations are conducted. Different amplitudes of random initial fluctuating velocity field are imposed. Two different instability mechanisms are observed within the range of Reynolds number studied. The first is a short-lived, nonlinear, long-wave instability which is observed during the acceleration phase, and the second is a broadband instability that occurs during the deceleration phase. Transition from a laminar to turbulent state is observed to follow two different breakdown pathways: the first follows the sequence of $K$-type secondary instability of a near-wall boundary layer at comparatively lower Reynolds number and the second one follows a breakdown path similar to that of free shear layers. Overall characteristics of the flow are categorized into four regimes as: (i) laminar; (ii) disturbed laminar; (iii) transitional; and (iv) turbulent. Our categorization into four regimes is consistent with earlier works. However, this study is able to provide more specific definitions through the instability characteristics and the turbulence breakdown process.

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ZAKI, TAMER A., JAN G. WISSINK, WOLFGANG RODI, and PAUL A. DURBIN. "Direct numerical simulations of transition in a compressor cascade: the influence of free-stream turbulence." Journal of Fluid Mechanics 665 (October 27, 2010): 57–98. http://dx.doi.org/10.1017/s0022112010003873.

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The flow through a compressor passage without and with incoming free-stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of free-stream disturbances. When exposed to free-stream forcing, the boundary layer remains attached due to transition to turbulence upstream of the laminar separation point. Three types of breakdowns are observed; they combine characteristics of natural and bypass transition. In particular, instability waves, which trace back to discrete modes of the base flow, can be observed, but their development is not independent of the Klebanoff distortions that are caused by free-stream turbulent forcing. At a higher turbulence intensity, the transition mechanism shifts to a purely bypass scenario. Unlike the pressure side, the suction surface boundary layer separates independent of the free-stream condition, be it laminar or a moderate free-stream turbulence of intensityTu~ 3%. Upstream of the separation, the amplification of the Klebanoff distortions is suppressed in the favourable pressure gradient (FPG) region. This suppression is in agreement with simulations of constant pressure gradient boundary layers. FPG is normally stabilizing with respect to bypass transition to turbulence, but is, thereby, unfavourable with respect to separation. Downstream of the FPG section, a strong adverse pressure gradient (APG) on the suction surface of the blade causes the laminar boundary layer to separate. The separation surface is modulated in the instantaneous fields of the Klebanoff distortion inside the shear layer, which consists of forward and backward jet-like perturbations. Separation is followed by breakdown to turbulence and reattachment. As the free-stream turbulence intensity is increased,Tu~ 6.5%, transitional turbulent patches are initiated, and interact with the downstream separated flow, causing local attachment. The calming effect, or delayed re-establishment of the boundary layer separation, is observed in the wake of the turbulent events.

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Jost, Dominic, and Kai Nagel. "Probabilistic Traffic Flow Breakdown in Stochastic Car-Following Models." Transportation Research Record: Journal of the Transportation Research Board 1852, no. 1 (January 2003): 152–58. http://dx.doi.org/10.3141/1852-19.

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Whether traffic displays multiple phases (e.g., laminar, jammed, synchronized) has been much discussed. Computational evidence is presented that a stochastic car-following model can be moved from two phases (laminar and jammed) to one phase by changing one of its parameters. Models with two phases show three states. Two of them are homogeneous and correspond to the two phases. The third state consists of a mix of the two phases (phase coexistence). Although the gas–liquid analogy to traffic models has been widely discussed, no traffic-related model ever displayed a completely understood stochastic version of that transition. A stochastic model is important to the understanding of the potentially probabilistic nature of the transition. If indeed two-phase models describe certain aspects correctly, predictions for breakdown probabilities can be made. Alternatively, if one-phase models describe these aspects better, there is no breakdown. Interestingly, such one-phase models can still allow for jam formation on a small scale, which may give the impression of two-phase dynamics.

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Zang, Thomas A., and M. Yousuff Hussaini. "Multiple paths to subharmonic laminar breakdown in a boundary layer." Physical Review Letters 64, no. 6 (February 5, 1990): 641–44. http://dx.doi.org/10.1103/physrevlett.64.641.

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Більше джерел

Дисертації з теми "Laminar breakdown"

Brandt, Luca. "Study of generation, growth and breakdown of streamwise streaks in a Blasius boundary layer." Licentiate thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1256.

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Transition from laminar to turbulent flow has beentraditionally studied in terms of exponentially growingeigensolutions to the linearized disturbance equations.However, experimental findings show that transition may occuralso for parameters combinations such that these eigensolutionsare damped. An alternative non-modal growth mechanism has beenrecently identified, also based on the linear approximation.This consists of the transient growth of streamwise elongateddisturbances, mainly in the streamwise velocity component,called streaks. If the streak amplitude reaches a thresholdvalue, secondary instabilities can take place and provoketransition. This scenario is most likely to occur in boundarylayer flows subject to high levels of free-stream turbulenceand is the object of this thesis. Different stages of theprocess are isolated and studied with different approaches,considering the boundary layer flow over a flat plate. Thereceptivity to free-stream disturbances has been studiedthrough a weakly non-linear model which allows to disentanglethe features involved in the generation of streaks. It is shownthat the non-linear interaction of oblique waves in thefree-stream is able to induce strong streamwise vortices insidethe boundary layer, which, in turn, generate streaks by thelift-up effect. The growth of steady streaks is followed bymeans of Direct Numerical Simulation. After the streaks havereached a finite amplitude, they saturate and a new laminarflow, characterized by a strong spanwise modulation isestablished. Using Floquet theory, the instability of thesestreaks is studied to determine the features of theirbreakdown. The streak critical amplitude, beyond which unstablewaves are excited, is 26% of the free-stream velocity. Theinstability appears as spanwise (sinuous-type) oscillations ofthe streak. The late stages of the transition, originating fromthis type of secondary instability, are also studied. We foundthat the main structures observed during the transition processconsist of elongated quasi-streamwise vortices located on theflanks of the low speed streak. Vortices of alternating signare overlapping in the streamwise direction in a staggeredpattern.

Descriptors:Fluid mechanics, laminar-turbulenttransition, boundary layer flow, transient growth, streamwisestreaks, lift-up effect, receptivity, free-stream turbulence,nonlinear mechanism, streak instability, secondary instability,Direct Numerical Simulation.

QC 20100518

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Silva, Guilherme Araújo Lima da. "Transferência de calor e massa no escoamento bifásico em torno de aerofólios equipados com sistemas de antigelo aeronáuticos." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-27032009-082825/.

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Há a necessidade de prevenir formação de gelo nas asas e nos estabilizadores de aeronaves, pois as formas de gelo podem causar a degradação do desempenho aerodinâmico, o aumento de peso, bem como dificuldades de controle e manobra que, em casos críticos, leva a uma diminuição da margem de segurança operacional. Quando as aeronaves atravessam nuvens com gotículas de água sub-resfriadas, ou seja, em equilíbrio metaestável, o crescimento de gelo ocorre nas superfícies não protegidas. Usualmente, os sistemas antigelo térmicos de aerofólios são projetados, desenvolvidos e certificados com o auxílio de programas de simulação numérica. O presente trabalho visa desenvolver e implementar um modelo matemático para prever a transferência de calor e massa no escoamento bidimensional bifásico em torno de aerofólios de uso aeronáuticos, equipados com sistema de antigelo térmico operando em regime permanente. Em condições de formação de gelo, é necessário aquecer o bordo de ataque e controlar a temperatura da região protegida para que não ocorra formação de gelo. O sistema de aquecimento compensa os efeitos do resfriamento imposto principalmente pelos mecanismos acoplados de evaporação e transferência de calor por convecção, que são causados pelo escoamento do ar carregado de gotículas sub-resfriadas e pelo escoamento da água líquida residual. O modelo deverá estimar a distribuição de temperaturas de superfície e o coeficiente de transferência de calor com precisão ao uso em aplicações aeronáuticas. O presente trabalho implementou novos submodelos para: 1) estimar a molhabilidade da superfície do aerofólio por meio de um modelo matemático para caracterizar o escoamento da água líquida residual na padrão de filme e de filetes; 2) avaliar o comportamento dinâmico e térmico da camada-limite laminar e turbulenta por meio de análises integral e diferencial, que considera efeitos do gradiente de pressão, da transição laminar-turbulenta, da transpiração e da não uniformidade de temperatura da superfície e 3) estimar o início e o término da região de transição laminar-turbulenta. O presente trabalho seguiu um processo de desenvolvimento de código numérico que: verificou os resultados de cada submodelo separadamente para depois implementados no modelo do antigelo; validou os resultados da simulação de desempenho do sistema antigelo com os novos submodelos implementados. Os resultados obtidos foram considerados satisfatórios para o modelo do antigelo que utilizou os submodelos de ruptura de filme e formação de filetes pelo critério da Energia Mecânica Total Mínima, de camada-limite diferencial compressível e de previsão da transição laminar-turbulenta por correlações algébricas, que consideraram efeitos do gradiente de pressão e do nível de turbulência ao longe.
It is required to prevent ice accretion on wings and horizontal stabilizers because it may cause aerodynamic performance degradation, weight increase, flight control difficulties and, in critical cases, may lead to operational safety margins reduction. When aircraft flies through clouds containnig supercooled water droplets, which are in metastable equilibrium, ice will form in all non-protected surfaces. Usually, anti-ice protection systems are designed, developed and certified with a support from a numerical tool. The present describes the development and implementation of a mathematical model for prediction of heat and mass transfer in two-phase flow around airfoils, which are equipped with thermal anti-ice system and operating in steady state regime. Under icing conditions, it is necessary to heat and control the temperature of the airfoil surface at leading edge region to prevent ice formation. The heating system balances the evaporative cooling effects, which are caused by the coupled heat and mass convection transfer, imposed by the air flow loaded with supercooled water droplets and the runback water flow around the airfoil. The present work implemented submodels to: 1) estimate airfoil surface wetness factor by adopting a liquid water film flow model as well as a rivulet formation and flow model; 2) evaluate laminar and turbulent boundary layers with pressure gradient and laminar-turbulent transition over nonisothermal and permeable airfoil surface by implementing differential boundary layer analysis and 3) predict the onset position and length of laminar-turbulent transition region. The present paper followed a validation and verification process during the numerical code development. All sub-models results were verified separately against experimental data before their inclusion in anti-ice model.The results of anti-ice model with selected submodels were validated against reference cases. The results were considered suficiently accurate when solving the film breakdown and rivulets formation by total mechanical energy method, compressible boundary layer by differential analysis and laminar-turbulent transition prediction by algebraic correlations, which considered pressure gradient and freestream turbulence level.

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Sharma, Sushank. "Transition laminaire turbulent dans les couches limites supersoniques : différents scénarios et contrôle possible Control of oblique-type breakdown in a supersonic boundary layer employing streaks Turbulent flow topology in supersonic boundary layer with wall heat transfer Laminar-to-turbulent transition in supersonic boundary layer : : Effects of initial perturbation and wall heat transfer Effect of thermo-mechanical non-equilibrium on the onset of transition in supersonic boundary layers." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMIR16.

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Les simulations numériques directes (DNS) des couches limites supersoniques adiabatiques et isothermes (chauffées et refroidies) sont effectuées. Deux différents scénarios de transition, à savoir la décomposition de type oblique et la transition de type 'by-pass', sont présentés en détail. Pour le scénario de transition de type oblique, les résultats montrent que les modes contrôles avec un nombre d'onde quatre à cinq fois supérieur au nombre fondamental se révèlent être bénéfiques pour contrôler la transition. Dans la première région après le forçage du mode de contrôle, la distorsion de flux moyenne (MFD) bénéfique générée en induisant le mode de contrôle est uniquement responsable de l'entrave à la croissance du mode fondamental. Globalement, le MFD et la partie tridimensionnelle du contrôle contribuent également à contrôler la rupture oblique. Les effets de paramètres physiques tels que la température de paroi, l'intensité de la perturbation et le 'baseflow' sont étudiés pour la transition de 'By-pass'. Les résultats concernant le scénario de by-pass révèlent que l'augmentation de l'intensité de la perturbation déplace le début de la transition en amont et augmente également la longueur de la région de transition. De plus, en dessous de 1 % des niveaux de perturbation, le refroidissement de la paroi stabilise le flux, tandis que l'inverse se produit à des valeurs plus élevées. L'existence d'un non-équilibre thermomécanique avance le début de la transition pour les cas chauffés alors que la paroi refroidie se comporte dans le sens opposé. Les analyses de la couche limite turbulente montrent que les facteurs thermiques influencent la topologie et l'inclinaison des structures tourbillonnaires. De plus, en ce qui concerne le flux de chaleur, un processus de transfert différent est dominant dans la région proche paroi pour la paroi refroidie
Direct numerical simulations (DNS) of both adiabatic and isothermal (heated and cooled) supersonic boundary layers are performed. Two different transition scenarios, namely the Oblique-type breakdown and the By-pass transition are presented in detail. For the oblique-type transition scenario, the results show that the control modes with four to five times the fundamental wavenumber are beneficial for controlling the transition. In the first region, after the control-mode forcing, the beneficial mean-flow distortion (MFD) generated by inducing the control mode is solely responsible for hampering the growth of the fundamental-mode. Globally, the MFD and the three-dimensional part of the control contribute equally towards controlling the oblique breakdown. Effects of physical parameters like wall-temperature, perturbation intensity and baseflow are investigated for the By-pass transition. The results regarding the by-pass scenario reveal that increasing the perturbation intensity moves the transition onset upstream and also increases the length of the transition region. Additionally, below 1% perturbation levels, wall-cooling stabilizes the flow while inverse happens at higher values. The existence of the thermo-mechanical non-equilibrium advances the onset of transition for the heated cases while the cooled wall behaves in the opposite sense. The analyses of the turbulent boundary layer show that the thermal factors influence the topology and inclination of the vortical structures. Moreover, regarding the heat flux, different transfer process is dominant in the near-wall region for the cooled wall

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Celep, Muhittin. "Τransitiοn dans les cοuches limites supersοniques : simulatiοns numériques directes et cοntrôle par stries". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMIR15.

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Dans les écoulements à haute vitesse, une traînée visqueuse élevée et des charges thermiques importantes sont des conséquences inhérentes sur les corps aérodynamiques. Ces effets augmentent de manière significative pendant la phase de transition lorsque la couche limite devient turbulente. Afin de réduire les risques de dommages mécaniques et de défaillances liées à la fatigue, des systèmes de protection thermique sont intégrés aux véhicules, ajoutant de la complexité aux aspects techniques et économiques de la conception. La solution réside dans l’acquisition d’une compréhension approfondie des mécanismes de transition et le développement de systèmes de contrôle pour prolonger la couche limite laminaire le long de la surface du véhicule. De nombreuses techniques de contrôle actives et passives peuvent être utilisées pour le contrôle de la transition, parmi lesquelles la méthode de l’emploi de stries émerge comme une approche particulièrement prometteuse. Cette méthode consiste à générer des stries étroitement espacées dans la direction de l’envergure, créant des zones alternées de haute et basse vitesse dans le champ d’écoulement. Bien que la méthode ait été testée récemment dans des écoulements supersoniques, démontrant son efficacité pour retarder la transition, sa pertinence doit être évaluée plus avant. Dans ce travail de recherche, des cas de DNS sont réalisés dans des régimes supersoniques et près-hypersoniques. Les stries sont introduites à l’aide d’une bande de soufflage/aspiration placée sur la paroi avant celle de la perturbation qui est utilisée pour déclencher la transition de manière “contrôlée”, forcée par une perturbation à une seule fréquence et longueur d’onde. L’enquête à Mach 2.0 confirme que les stries avec cinq fois la longueur d’onde fondamentale sont les plus bénéfiques pour le contrôle de la transition. De plus, le refroidissement améliore l’efficacité de la méthode, tandis que le chauffage détériore considérablement la capacité de contrôle des stries. La condition murale isotherme n’altère pas l’impact stabilisateur comparable de la déformation du flux moyen (DFM) et de la partie 3D du contrôle à Mach 2.0. Cependant, à Mach 4.5, tant le type d’instabilité que les caractéristiques des stries changent de manière significative. L’impact stabilisateur de la DFM devient presque absent, et la partie 3D du contrôle prédomine, les caractéristiques des stries n’étant plus considérées comme indépendantes de leur amplitude de perturbation initiale
In high-speed flows, elevated viscous drag and thermal loads are inherent outcomes over aerodynamic bodies. These effects escalate substantially during the transition phase when the boundary layer becomes turbulent. To mitigate potential mechanical damage and fatigue-related failures, thermal protection systems are integrated into vehicles, adding complexity to the technical and economic aspects of design. The solution lies in gaining a comprehensive understanding of transition mechanisms and developing control systems to prolong laminar boundary layer along the vehicle’s surface. Numerous active and passive control techniques can be employed for transition control, with the streak employment method emerging as a particularly promising approach. This method involves generating narrowly spaced streaks in the spanwise direction, creating alternating high and low-speed regions in the flow field. Although the method has only recently been tested in supersonic flows, demonstrating its effectiveness in delaying transition, its suitability needs to be assessed further. In this research work, direct numerical simulations are performed in supersonic and near-hypersonic regimes. Streaks are introduced through a blowing/suction strip placed at the wall prior to that of the perturbation which is used to trigger transition in a “controlled” fashion, forced by a single frequency and wavenumber disturbance. The investigation at Mach 2.0 confirms that streaks with five times the fundamental wavenumber are most beneficial for transition control. Additionally, cooling enhances the method’s effectiveness, while heating severely deteriorates the capability of control streaks. The isothermal wall condition does not alter the comparable stabilizing impact of the mean flow deformation (MFD) and the 3-D part of the control at Mach 2.0. However, at Mach 4.5, both the type of instability and the characteristics of the streaks change significantly. The stabilizing impact of the MFD becomes nearly absent, and the 3-D part of the control predominates, with the characteristics of the streaks no longer considered independent of their initial disturbance amplitude

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Gikas, Zacharias Z. "Effect of small pressure disturbances on the breakdown of round laminar and turbulent jets." Thesis, 1985. http://hdl.handle.net/10945/21295.

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Книги з теми "Laminar breakdown"

Zang, Thomas A. Multiple paths to subharmonic laminar breakdown in a boundary layer. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1989.

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Yousuff, Hussaini M., and Langley Research Center, eds. Multiple paths to subharmonic laminar breakdown in a boundary layer. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1990.

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United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., ed. Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1993.

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United States. National Aeronautics and Space Administration. Scientific and Technical Information Program, ed. Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling. [Washington, DC]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1993.

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United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., ed. Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling. [Washington, D.C.]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1993.

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El-Hady, Nabil M. Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling. Hampton, Va: Langley Research Center, 1993.

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United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., ed. Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling. [Washington, D.C.]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program, 1993.

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Gikas, Zacharias Z. Effect of small pressure disturbances on the breakdown of round laminar and turbulent jets. 1985.

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Частини книг з теми "Laminar breakdown"

Herbert, Thorwald, and Jeffrey D. Crouch. "Threshold Conditions for Breakdown of Laminar Boundary Layers." In Laminar-Turbulent Transition, 93–101. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84103-3_7.

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Kachanov, Yury S. "Nonlinear Breakdown of Laminar Boundary Layer." In Nonlinear Instability of Nonparallel Flows, 21–51. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-85084-4_2.

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Tso, Jin, Shing-Ing Chang, and Ron F. Blackwelder. "On the Breakdown of a Wave Packet Disturbance in a Laminar Boundary Layer." In Laminar-Turbulent Transition, 199–214. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84103-3_17.

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Kachanov, Yu S., V. V. Kozlov, V. Ya Levchenko, and M. P. Ramazanov. "On Nature of K-Breakdown of a Laminar Boundary Layer. New Experimental Data." In Laminar-Turbulent Transition, 61–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-82462-3_7.

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Boiko, A. V., V. V. Kozlov, V. V. Syzrantsev, and V. A. Scherbakov. "Experimental Study of Secondary Instability and Breakdown in a Swept Wing Boundary Layer." In Laminar-Turbulent Transition, 289–95. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-79765-1_34.

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Matsubara, M., A. A. Bakchinov, J. H. M. Fransson, and P. H. Alfredsson. "Growth and breakdown of streaky structures in boundary layer transition induced by free stream turbulence." In Laminar-Turbulent Transition, 371–76. Berlin, Heidelberg: Springer Berlin Heidelberg, 2000. http://dx.doi.org/10.1007/978-3-662-03997-7_55.

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Kachanov, Y. S. "Secondary and Cascade Resonant Instabilities of Boundary Layers. Wave-Resonant Concept of a Breakdown and its Substantiation." In Laminar-Turbulent Transition, 65–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84103-3_5.

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Asai, Masahito, Masayuki Minagawa, and Michio Nishioka. "Instability and Breakdown of the Three-Dimensional High-Shear Layer Associated with a Near-Wall Low-Speed Streak." In Laminar-Turbulent Transition, 269–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 2000. http://dx.doi.org/10.1007/978-3-662-03997-7_39.

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Zang, Thomas A. "Aspects of Laminar Breakdown in Boundary-Layer Transition." In Instability, Transition, and Turbulence, 377–87. New York, NY: Springer New York, 1992. http://dx.doi.org/10.1007/978-1-4612-2956-8_37.

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Ji-sheng, Luo, Wang Xin-jun, and Zhou Heng. "INHERENT MECHANISM OF BREAKDOWN IN LAMINAR-TURBULENT TRANSITION." In Fluid Mechanics and Its Applications, 267–73. Dordrecht: Springer Netherlands, 2006. http://dx.doi.org/10.1007/1-4020-4159-4_36.

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Тези доповідей конференцій з теми "Laminar breakdown"

STETSON, KENNETH, and ROGER KIMMEL. "On the breakdown of a hypersonic laminar boundary layer." In 31st Aerospace Sciences Meeting. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-896.

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PRUETT, C., and T. ZANG. "Direct numerical simulation of laminar breakdown in high-speed, axisymmetric boundary layers." In 30th Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1992. http://dx.doi.org/10.2514/6.1992-742.

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Adams, N., and L. Kleiser. "Numerical simulation of fundamental breakdown of a laminar boundary-layer at Mach 4.5." In 5th International Aerospace Planes and Hypersonics Technologies Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-5027.

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Watmuff, Jonathan H. "Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45685.

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Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.

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Ikeda, Yuji, Atsushi Nishiyama, Nobuyuki Kawahara, Eiji Tomita, and Takashi Nakayama. "Local equivalence ratio measurement of CH4/Air and C3H8/air laminar flames by laser-induced breakdown spectroscopy." In 44th AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-965.

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Eaves, L. "Quantum Hall Effect Breakdown Steps due to an Instability of Laminar Flow against Electron-Hole Pair Formation." In Proceedings of Nobel Symposium 116. WORLD SCIENTIFIC, 2001. http://dx.doi.org/10.1142/9789812811004_0029.

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Kro¨ner, Martin, Jassin Fritz, and Thomas Sattelmayer. "Flashback Limits for Combustion Induced Vortex Breakdown in a Swirl Burner." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30075.

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Flame flashback from the combustion chamber into the mixing zone limits the reliability of swirl stabilized lean premixed combustion in gas turbines. In a former study, the combustion induced vortex breakdown (CIVB) has been identified as a prevailing flashback mechanism of swirl burners. The present study has been performed to determine the flash-back limits of a swirl burner with cylindrical premixing tube without centerbody at atmospheric conditions. The flashback limits, herein defined as the upstream flame propagation through the entire mixing tube, have been detected by a special optical flame sensor with a high temporal resolution. In order to study the effect of the relevant parameters on the flashback limits, the burning velocity of the fuel has been varied using four different natural gas-hydrogen-mixtures with a volume fraction of up to 60% hydrogen. A simple approach for the calculation of the laminar flame speeds of these mixtures is proposed which is used in the next step to correlate the experimental results. In the study, the preheat temperature of the fuel mixture was varied from 100 °C to 450 °C in order to investigate influence of the burning velocity as well as the density ratio over the flame front. Moreover, the mass flow rate has been modified in a wide range as an additional parameter of technical importance. It was found that the quenching of the chemical reaction is the governing factor for the flashback limit. A Peclet number model was successfully applied to correlate the flashback limits as a function of the mixing tube diameter, the flow rate and the laminar burning velocity. Using this model, a quench factor can be determined for the burner, which is a criterion for the flashback resistance of the swirler and which allows to calculate the flashback limit for all operating conditions on the basis of a limited number of flashback tests.

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Watmuff, Jonathan H. "Sinuous Streak Instability and Breakdown in a Blasius Boundary Layer." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-31322.

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A narrow low-speed streamwise streak is deliberately introduced into an otherwise extremely spanwise uniform Blasius boundary layer. The streak shares many of the characteristics of Klebanoff modes known to be responsible for bypass transition at moderate Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream (u/U1 < 0.05%), the layer remains laminar to the end of the test section (Rx = 1.4 × 106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A harmonic disturbance is used to excite a sinuous form of instability, which grows over a considerable streamwise distance before breakdown of the streak occurs, which leads to the formation of a turbulent wedge. Detailed measurements show that new streaks are formed on either side during the breakdown process. The characteristics of the wedge are examined over a considerable streamwise distance. A similar mechanism appears to be responsible for the spanwise growth of the wedge since a span-wise succession of new streaks is observed in the early stages of its development.

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Schmidt, Jacob, and Biswa Ganguly. "Transition from stable laminar to highly unstable behavior in premixed propane/air flame with sub-breakdown electric field." In 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2012. http://dx.doi.org/10.2514/6.2012-377.

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Abraham, J. P., E. M. Sparrow, J. C. K. Tong, and W. J. Minkowycz. "Intermittent Flow Modeling: Part I—Hydrodynamic and Thermal Modeling of Steady, Intermittent Flows in Constant Area Ducts." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22858.

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A model for predicting fluid flow and convective heat transfer in all flow regimes has been implemented for steady mainflows in pipes and ducts of constant cross section. The key feature of the model is its capability to predict transitions between purely laminar and purely turbulent flow, while the latter flows are also predicted with high accuracy. The flow regime need not be specified in advance but is determined automatically as the flow evolves during its passage along the pipe or duct. Intermittently in the transition regime is fully accounted. It was shown that fully developed flows are necessarily restricted to either the laminar regime or the turbulent regime, but that a fully developed intermittent regime exists. The effects of the flow conditions at the inlet of the pipe or duct, velocity profile shape and turbulence intensity, on the subsequent transitions were quantified. To facilitate the heat transfer analysis, the turbulent-Prandtl-number concept, widely used to inter-relate the turbulent viscosity and thermal conductivity, was extended to encompass both intermittent and laminar flows. The presented results include all-flow-regime fully developed friction factors and fully developed Nusselt numbers. The locations where laminar-flow breakdown occurs and where fully developed begins are also presented.

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Звіти організацій з теми "Laminar breakdown"

Nayfeh, Ali H. Laminar Boundary-Layer Breakdown. Fort Belvoir, VA: Defense Technical Information Center, July 1992. http://dx.doi.org/10.21236/ada254489.

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Glezer, A., Y. Katz, and I. Wygnanski. On the Breakdown of the Wave Packet Trailing a Turbulent Spot in a Laminar Layer. Fort Belvoir, VA: Defense Technical Information Center, January 1986. http://dx.doi.org/10.21236/ada179607.

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