Дисертації з теми "Boundary-Layer Instability"
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Nash, Emma Clare. "Boundary layer instability noise on aerofoils." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337698.
Повний текст джерелаImayama, Shintaro. "Studies of the rotating-disk boundary-layer flow." Doctoral thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-158973.
Повний текст джерелаQC 20150119
Imayama, Shintaro. "Experimental study of the rotating-disk boundary-layer flow." Licentiate thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95147.
Повний текст джерелаQC 20120529
Masad, Jamal A. "On subharmonic instability in boundary layers." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45783.
Повний текст джерелаThe subharmonic instability in two-dimensional boundary layer on a flat plate is analyzed using the parametric instability model and the resonant triad model. The problems arising from both models are solved numerically using the shooting technique and results are presented. It is found that in the presence of a strong interaction (e.g., large amplitude of the two-dimensional wave), results from the resonant triad model are inaccurate as compared with the experimental data and the t results from the parametric instability model. This is mainly because the resonant triad model is a weakly nonlinear model, and it does not account for the modification of the eigenfunctions of the interacting waves which really takes place as we find out from the experiments.
The parametric instability model is a powerful model, despite all the assumptions included. The model, however, does not introduce a clear understanding of how the subharmonic mode originates from the three-dimensional Tollmien-Schlichting modes.
For a weak interaction results from the resonant triad model and the parametric instability model get close to each other.
Master of Science
Appelquist, Ellinor. "The rotating-disk boundary-layer flow studied through numerical simulations." Doctoral thesis, KTH, Mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200827.
Повний текст джерелаQC 20170203
Savin, Deborah Jane. "Linear and nonlinear aspects of interactive boundary layer transition." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243306.
Повний текст джерелаAppelquist, Ellinor. "Direct numerical simulations of the rotating-disk boundary-layer flow." Licentiate thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146087.
Повний текст джерелаQC 20140708
Tyagi, P. K. "Linear Instability Of Laterally Strained Constant Pressure Boundary Layer Flows." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/265.
Повний текст джерелаStrange, Michael Edward. "The effect of surface cooling on compressible boundary-layer instability." Thesis, University of Hull, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296279.
Повний текст джерелаRoland, Hannah. "Instability and receptivity of subsonic flow in the boundary layer." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/64819.
Повний текст джерелаRobey, H. F. Liepmann H. W. Liepmann H. W. "The nature of oblique instability waves in boundary layer transition /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-05242007-150746.
Повний текст джерелаFinnis, M. V. "Centrifugal instability of a laminar boundary layer on a concave surface." Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332090.
Повний текст джерелаWang, Yaxing. "Instability and transition of boundary layer flows disturbed by steps and bumps." Thesis, Queen Mary, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404889.
Повний текст джерелаHosseini, Seyed Mohammd. "On stability, transition and turbulence in three-dimensional boundary-layer flows." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177617.
Повний текст джерелаQC 20151125
Wu, Jie [Verfasser]. "Boundary-layer Instability Experiments in a Tandem Nozzle Supersonic Wind Tunnel / Jie Wu." Aachen : Shaker, 2015. http://d-nb.info/106904864X/34.
Повний текст джерелаSamad, Abdul. "The convective instability of the boundary-layer flow over families of rotating spheroids." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/27576.
Повний текст джерелаAbdulameer, Mohammed Alaa. "The convective instability of BEK family of non-Newtonian rotating boundary-layer flows." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/42800.
Повний текст джерелаWu, Peng, Xiquan Dong, Baike Xi, Yangang Liu, Mandana Thieman, and Patrick Minnis. "Effects of environment forcing on marine boundary layer cloud-drizzle processes." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/624343.
Повний текст джерелаHögberg, Markus. "Optimal Control of Boundary Layer Transition." Doctoral thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3245.
Повний текст джерелаBrandt, Luca. "Numerical studies of bypass transition in the Blasius boundary layer." Doctoral thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3517.
Повний текст джерелаExperimental findings show that transition from laminar toturbulent ow may occur also if the exponentially growingperturbations, eigensolutions to the linearised disturbanceequations, are damped. An alternative non-modal growthmechanism has been recently identi fied, also based on thelinear approximation. This consists of the transient growth ofstreamwise elongated disturbances, with regions of positive andnegative streamwise velocity alternating in the spanwisedirection, called streaks. These perturbation are seen toappear in boundary layers exposed to signi ficant levels offree-stream turbulence. The effect of the streaks on thestability and transition of the Blasius boundary layer isinvestigated in this thesis. The analysis considers the steadyspanwise-periodic streaks arising from the nonlinear evolutionof the initial disturbances leading to the maximum transientenergy growth. In the absence of streaks, the Blasius pro filesupports the viscous exponential growth of theTollmien-Schlichting waves. It is found that increasing thestreak amplitude these two-dimensional unstable waves evolveinto three-dimensional spanwiseperiodic waves which are lessunstable. The latter can be completely stabilised above athreshold amplitude. Further increasing the streak amplitude,the boundary layer is again unstable. The new instability is ofdifferent character, being driven by the inectional pro filesassociated with the spanwise modulated ow. In particular, it isshown that, for the particular class of steady streaksconsidered, the most ampli fied modes are antisymmetric andlead to spanwise oscillations of the low-speed streak (sinuousscenario). The transition of the streak is then characterisedby the appearance of quasi-streamwise vorticesfollowing themeandering of the streak.
Simulations of a boundary layer subjected to high levels offree-stream turbulence have been performed. The receptivity ofthe boundary layer to the external perturbation is studied indetail. It is shown that two mechanisms are active, a linearand a nonlinear one, and their relative importance isdiscussed. The breakdown of the unsteady asymmetric streaksforming in the boundary layer under free-stream turbulence isshown to be characterised by structures similar to thoseobserved both in the sinuous breakdown of steady streaks and inthe varicose scenario, with the former being the mostfrequently observed.
Keywords:Fluid mechanics, laminar-turbulent transition,boundary layer ow, transient growth, streamwise streaks,lift-up effect, receptivity, free-stream turbulence, secondaryinstability, Direct Numerical Simulation.
Stewart, I. J. "A model for transition by attachment line contamination and an examination of cross-flow instability in three-dimensional boundary layers." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380625.
Повний текст джерелаHosseini, Seyed M., Ardeshir Hanifi, and Dan Henningson. "Effect of freestream turbulence on roughness-induced crossflow instability." KTH, Stabilitet, Transition, Kontroll, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-123192.
Повний текст джерелаQC 20130604
Khapko, Taras. "Transition to turbulence in the asymptotic suction boundary layer." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141344.
Повний текст джерелаQC 20140213
Alveroğlu, Burhan. "The convective instability of the BEK system of rotating boundary-layer flows over rough disks." Thesis, University of Leicester, 2016. http://hdl.handle.net/2381/37977.
Повний текст джерелаBrandt, 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.
Повний текст джерелаTransition 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
Cherubini, Stefania. "Linear and non-linear global instability of attached and separated boundary-layer flows over a flat plate." Paris, ENSAM, 2010. http://www.theses.fr/2010ENAM0012.
Повний текст джерелаLe but de cette thèse est de décrire en détail la dynamique linéaire et non linéaire d'une couche limite attachée sur une plaque plane à bas nombre de Reynolds. La dynamique linéaire, pilotée par les interactions entre les vecteurs propres non-orthogonaux, est étudiée à travers deux méthodes différentes d’instabilité globale : une analyse globale aux vecteurs propres et une optimisation directe-adjointe. Dans ces analyses globales, aucune structure spatiale n’est imposée à priori pour la perturbation, les effets convectifs dus au fort non parallélisme de l’écoulement sont pris en compte. Pour le cas de la couche limite décollée, le déclenchement des instationnarités a été clarifié : i) pour une forte amplification des perturbations de nature convective et bidimensionnelle ; ii) pour des effets de non normalité longitudinale engendrant le phénomène du flapping ; iii) pour une forte sensibilité vis-à-vis d’un forçage harmonique ; iv) pour un monde tridimensionnel globalement instable. Pour une couche limite attachée, le but a été d’identifier les perturbations localisées caractérisées par des fréquences multiples dans les directions longitudinales et transversales de l’écoulement, induisant une amplification de l’énergie des perturbations. Pour évaluer les effets les effets de la non linéarité dans les mécanismes d’instabilité identifiés par les analyses de stabilité globale, des simulations numériques directes ont été réalisées pour les écoulements de couche limite attachées ou décollées, bidimensionnelles et tridimensionnelles. La dynamique des perturbations permettant une plus rapide vers la turbulence a été étudiée. Différents scénarios de transition ont été observés, les différents mécanismes de transition ont été analysés
Pryce, David. "Receptivity of a boundary-layer subject to vertical vibrations and the secondary instability of spanwise modulated shear flows." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24907.
Повний текст джерелаGottmann, Matthias 1964. "Two-dimensional Navier Stokes simulations of instability waves in a flat plate boundary layer flow at M = 4.5." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278125.
Повний текст джерелаAdler, Michael C. "On the Advancement of Phenomenological and Mechanistic Descriptions of Unsteadiness in Shock-Wave/Turbulent-Boundary-Layer Interactions." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553543774661509.
Повний текст джерелаBrynjell-Rahkola, Mattias. "Studies on instability and optimal forcing of incompressible flows." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218172.
Повний текст джерелаQC 20171124
Yadala, Venkata Srikar. "Plasma-flow interfaces for instability control." Thesis, Poitiers, 2020. http://www.theses.fr/2020POIT2292.
Повний текст джерелаThe research presented in this thesis focuses on the design and use of dielectric barrier discharge (DBD) plasma actuators with thin and complex geometry electrodes to exert instability control on two flow configurations whose dynamics are governed by primary and/or secondary instability mechanisms.The case of a three-dimensional boundary layer as encountered on a swept wing is studied using two forcing strategies to manipulate the transition induced by a stationary instability phenomenon. Here, an array of discrete roughness elements (DRE) is installed upstream of the DBD forcing in order to lock the origin and evolution of the stationary cross-flow (CF) vortices in the boundary layer. The first forcing approach is upstream flow deformation (UFD). The second approach based on direct modification of the base flow is also introduced (BFM). Independent of the forcing applied, a transition delay is observed. However, as the CF vortices are strongly amplified due to the use of DRE, the action by UFD approach can lead both to a direct attenuation of the CF vortices as envisaged but also to an unintentional action on the inflectional nature of the base flow. The BFM method results in a direct attenuation of the CF velocity component, which is also confirmed by a theoretical study of instability under the effect of the DBD actuator through a simplified model. This is not only the first experimental demonstration of transition delay on a swept wing using plasma actuators, but also the first experimental proof of concept of the BFM strategy.The wake of a plane mixed layer with a thick edge and the primary and secondary instability phenomena responsible for the spatio-temporal expansion of the wake are also studied. Frequency and then spatial forcing conditions are successively tested and analysed by spectral approach (spectral proper orthogonal decomposition, SPOD) on experimental data from multi-field time-resolved particle image velocimetry. The primary instability is excited by a spatially uniform forcing pulsed at the naturally most amplified frequency. It is shown that the mean component of the flow is not modified while the spectral content of the mixing layer is largely affected. This forcing leads, in particular, to the inhibition of the pairing of vortical structures due to the attenuation of sub-harmonic instabilities. Conversely, direct forcing of sub-harmonic instabilities results in a reinforcement of the pairing phenomena, leading to a higher growth rate of the mixing layer. Finally, spatially modulated forcing results in a growth that varies according to the spanwise position, which reflects both the reinforcement and the spatial modulation of large-scale spanwise structures. The modulation of the forcing according to the scale of the mixing layer always allows the modification of the spanwise structures but in addition, the coalescence of the streamwise and spanwise structures is favoured.The research work carried out confirms the ability of DBD plasma actuators to exert a forcing modulated both temporally and spatially. The proposed actuators allow only a partial control of the instability phenomena in the three-dimensional boundary layer while the high receptivity of the initial region of a mixing layer has led to significant results both on the dynamics of spanwise and streamwise coherent structures. Thanks to a large reduction of the electrical power consumed in the case of spatially modulated forcing, the efficiency of the control system is greatly improved
北村, 圭一, Keiichi KITAMURA, 佳朗 中村 та Yoshiaki NAKAMURA. "極超音速衝撃波干渉流れにおける空力加熱の数値解析". 日本航空宇宙学会, 2008. http://hdl.handle.net/2237/13871.
Повний текст джерелаDas, Shyama Prasad. "An Experimental Study Of Instabilities In Unsteady Separation Bubbles." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/290.
Повний текст джерелаMartínez, Germán Andrés Gaviria. "Towards natural transition in compressible boundary layers." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-24052017-114027/.
Повний текст джерелаNo presente trabalho, um código DNS (Direct Numerical Simulation) foi desenvolvido para abordar problemas de transição para turbulência em camada limite subsônica compressível em uma placa plana. Foram realizados testes de validação de código , nos regimes linear e não linear do processo de transição, nos regimes incompressível e compressível. O foco do presente trabalho é estudar transição natural modelada por meio de pacotes de onda em camada limite compressível subsônica, e realizar uma análise preliminar da transição induzida por ruído branco. Três assuntos principais foram considerados: uma simulação DNS e uma análise comparativa com o experimento (MEDEIROS; GASTER, 1999b) sobre a evolução de um pacote de ondas em camada limite incompressível, a influência da compressibilidade na evolução de pacotes de ondas no regime subsônico, e por último, um estudo preliminar da transição induzida por ruído branco em Mach 0.2 e Mach 0.9. As comparações realizadas entre a solução numérica e os dados experimentais mostram uma boa concordância, nos regimes linear e não linear, tanto no espaço físico quanto no espaço de Fourier. A simulação numérica deste experimento e a análise realizada neste trabalho, não são encontradas na literatura para o regime incompressível. A análise modal não linear aplicada aos resultados, permitiu identificar a presença das ressonâncias tipo H e tipo K no pacote de ondas. A influência da compressibilidade na evolução dos pacotes de onda foi estudada em Mach 0.7 e Mach 0.9. Na literatura não há trabalhos sobre pacotes de ondas no regime sub- sônico. No regime linear da transição, os modos oblíquos resultam ser os mais instáveis para Mach > 0.7, como era de esperar, de acordo com os resultados da literatura. No regime não linear, foram observadas estrias de moderada amplitude, associadas com modos de baixa frequência que acabam decaindo. O pacote de ondas em Mach 0.9 apresentou amplificação não linear somente na banda subharmônica, que pode ser associada com transição tipo H ou ressonância dessintonizada. No entanto, o comportamento geral neste regime é estabilizante. Por sua vez, a interação entre pacotes de ondas em Mach 0.9 mostrou um comportamento desestabilizante, pois a interação acaba gerando amplificação não linear em modos que decaem no pacote isolado. Os modos amplificados sugerem a presença do mecanismo de transição oblíqua. Finalmente, a evolução da mesma perturbação constituída por ruído branco em Mach 0.2 e Mach 0.9, resultaram ser completamente diferentes. Na camada limite incompressível foram observados vórtices tipo lambda, que poderiam ser gerados pela presença localizada das ressonâncias tipo H e/ou tipo K. No regime compressível foram observados vórtices distribuidos em todo o domínio, o que sugere a presença da transição oblíqua. Na transição gerada por ruído branco a compressibilidade teve uma influência maior que no pacote de ondas. Nas condições estudadas, a interação entre pacotes de ondas parece ser uma melhor representação do ruído branco no regime compressível.
Peerhossaini, Hassan. "L'instabilite d'une couche limite sur une paroi concave : les tourbillons de gortler." Paris 6, 1987. http://www.theses.fr/1987PA066023.
Повний текст джерелаSiddiqui, Muhammad Ehtisham. "Experimental study of natural and forced instabilities and transition of a rotating-disk boundary-layer flow." Thesis, Ecully, Ecole centrale de Lyon, 2011. http://www.theses.fr/2011ECDL0006/document.
Повний текст джерелаThis dissertation concerns experimental work on the instability and transition of the rotating-disk boundary-layer flow. In the case of the natural flow (i.e. without forcing), measurements of mean-flow profiles, frequency spectra and phase-locked averages of the velocity time series allow us to distinguish different flow regimes as a function of nondimensional distance, R, from the disk axis. As R increases, the mean-velocity profiles initially follow the von Kármán solution. At higher R, departures arise and increase with R. These departures are due to the spatial growth of boundary-layer instability modes (cross-flow vortices), whose radial growth rates are found to match linear-theory predictions. The flow becomes transitional at R ≈ 530 and fully turbulent by R ≈ 600. The profiles in the fully turbulent region follow the log law of turbulent boundary layers and the velocity spectra exhibit Kolmogorov-type power laws. To study the response to forcing, an experimental apparatus has been designed which allows the excitation of stationary (in thelaboratory frame of reference) disturbances or disturbances which rotate with a frequency which can be varied independently of the disk rotation rate. The flow response to both types of forcing and two forcing-element geometries was studied. Stationary forcing produces a wake which decays with distance from the element, in agreement with theory. Forcing due to rotating elements can generate growing wavepacket-like disturbances, which although nonlinear, follow trajectories close to linear-theory predictions
Passaggia, Pierre-yves. "Instabilités d'écoulements décollés et leur contrôle." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4790/document.
Повний текст джерелаThe dynamics and control of a separated boundary-layer flow have been investigated. Separation is triggered by a bump mounted on a flat plate and the transition dynamics has been investigated experimentally. For a certain parameter range, the recirculation region is subject to self-sustained low-frequency oscillations, and results from the numerical simulation for the same geometry are recovered. These results show that low frequency oscillations, observed mainly in compressible flow regimes, are inherent to elongated recirculation bubbles.The control of this low-frequency instability has been investigated using modern control theory based on two complementary approaches. Feedback control of the linear perturbation dynamics is first considered. Global instability modes are used to build reduced-order estimators. This model reduction gives rise to low-dimensional compensators capable of controlling the unstable dynamics. Once coupled to the unstable linearised Navier-Stokes system, the compensator is seen to succesfully control the unstable dynamics. The control of the nonlinear dynamics is then investigated using adjoint-based optimisation procedures. This method is used to compute control laws based on a complete knowledge of the nonlinear dynamics. Although the low-frequency instability is clearly attenuated, it seems difficult to control the flow towards its steady state, using only a few blowing/suction actuators localized on the wall
Siddiqui, Muhammad. "Experimental study of natural and forced instabilities and transition of a rotating-disk boundary-layer flow." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00589797.
Повний текст джерелаFadla, Fawzi. "Caractérisation expérimentale de la dynamique du décollement de couche limite induit par un gradient de pression adverse et un effet de courbure." Thesis, Valenciennes, 2014. http://www.theses.fr/2014VALE0022/document.
Повний текст джерелаThese investigations concern the characterization of unsteady phenomena associated to the boundary layer separation induced by both an adverse pressure gradient and a curvature effects. This kind of separation is very usual, particularly in the transport field. This study, essentially based on an experimental approach, is carried out in an hydrodynamic channel using non intrusive measurement techniques. They respect the very sensitive dynamics of the boundary layer separation phenomenon. The separation is, in our case, induced by a 2d obstacle without sharp corner. The studied flow regime is mainly turbulentand the analyzed Kármán number ranges from 60 to 730. The main aim of this study is to estimate the Reynolds number effects on the boundary layer separation length and even on the existence of such phenomenon, but also on the instabilities dynamics, identified in the literature especially for laminar flow regime. The measurements made within the framework of these works allowed, first to built a large experimental database, and secondly to establish that the boundary layer separation and also the associate instabilities, identified for laminar flow, persist even for higher Kármán number. The frequencies associated to the instabilities phenomena have been also identified as well as the characteristic parameters driving their dynamics. The instabilities space-time dynamic, in particular those of the flapping phenomenon were detailed using stochastic analysis. Finally, the large scales distribution associated with the unstable mechanisms (underlined by their spectral broadband frequency range) were also highlighted, as well asothers secondary dynamic phenomena. All these results, especially the identification of the key parameters driving the boundary layer separation, will turn out very useful to design afterward simplified models reproducing as faithfully as possible the separation dynamics and to be able to control them better
Lucas, Jean-Michel. "Étude et modélisation du phénomène de croissance transitoire et de son lien avec la transition Bypass au sein des couches limites tridimensionnelles." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0033/document.
Повний текст джерелаLe passage du régime laminaire au régime turbulent s’accompagne d’importantes modifications despropriétés physiques de la couche limite. La détermination précise de la transition est donc crucialedans de nombreux cas pratiques. Lorsque la couche limite se développe dans un environnementextérieur faiblement perturbé, la transition est gouvernée par l’amplification du mode propre le moinsstable. Lorsque l’intensité des perturbations extérieures augmente, des interactions multimodalesentraînent une amplification transitoire des perturbations. Ce phénomène peut conduire à unetransition prématurée, appelée transition Bypass. Les perturbations prennent alors la forme destries longitudinales de vitesse appelées modes de Klebanoff.L’objectif de cette thèse est d’étudier ce mécanisme linéaire de croissance transitoire et soninfluence sur l’amplification modale classique des perturbations. Cela passe par la déterminationdes perturbations les plus amplifiées au sein de la couche limite, appelées perturbations optimales.Ces perturbations optimales sont d’abord calculées pour des couches limites bidimensionnelles etcompressibles se développant sur des surfaces courbes. En particulier, on montre que les modes deKlebanoff évoluent vers les tourbillons de Görtler qui se forment sur des parois concaves. Le cas plusgénéral de couches limites tridimensionnelles est ensuite envisagé. Pour de telles configurations, lacroissance transitoire fournit une amplitude initiale aux instabilités transversales. Enfin, l’applicationdes outils développés dans cette thèse fournit de nouveaux résultats pour des cas d’écoulementsautour de géométries réalistes comme une aile en flèche
Desvigne, Damien. "Bruit rayonné par un écoulement subsonique affleurant une cavité cylindrique : caractérisation expérimentale et simulation numérique par une approche multidomaine d'ordre élevé." Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00589006.
Повний текст джерелаZeng, Yi Zhen, and 曾以真. "Ocean Boundary Layer instability." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/83370795733136126103.
Повний текст джерелаParziale, Nicholaus J. "Slender-Body Hypervelocity Boundary-Layer Instability." Thesis, 2013. https://thesis.library.caltech.edu/7808/1/Parziale_Thesis.pdf.
Повний текст джерелаWith novel application of optical techniques, the slender-body hypervelocity boundary-layer instability is characterized in the previously unexplored regime where thermo-chemical effects are important. Narrowband disturbances (500-3000 kHz) are measured in boundary layers with edge velocities of up to 5~km/s at two points along the generator of a 5 degree half angle cone. Experimental amplification factor spectra are presented. Linear stability and PSE analysis is performed, with fair prediction of the frequency content of the disturbances; however, the analysis over-predicts the amplification of disturbances. The results of this work have two key implications: 1) the acoustic instability is present and may be studied in a large-scale hypervelocity reflected-shock tunnel, and 2) the new data set provides a new basis on which the instability can be studied.
Downs, Robert 1982. "Environmental Influences on Crossflow Instability." Thesis, 2012. http://hdl.handle.net/1969.1/148060.
Повний текст джерелаRobey, Harry Francis III. "The Nature of Oblique Instability Waves in Boundary Layer Transition." Thesis, 1986. https://thesis.library.caltech.edu/2023/1/Robey_HF_1986.pdf.
Повний текст джерелаAn experimental study of both the weakly non-linear as well as the three-dimensional nature of boundary layer transition is conducted using the active surface heating technique of Liepmann et al. In the present study, this technique is extended to provide a means for controllably and repeatably introducing three-dimensional disturbances into a laminar boundary layer. A review of the surface heating technique is presented along with a discussion of some peculiarities encountered in extending this technique to three-dimensional geometries. A thorough description of the design and operation of a programmable 32-element heater array and the supporting instrumentation are given as well.
The heater array is first used to study the effect of weak nonlinearity on boundary layer transition. By keeping the forced disturbances as two-dimensional as possible, it is shown that the effects of weak non-linearity are relatively benign. The growth rates are seen to follow the linear theory up to perturbation amplitudes (τ'wτ̅w) of nearly twelve percent. The only deviation from the linear theory arises in the form of non-linearly generated harmonics phase-locked to the fundamental. It is concluded that although these non-linearly generated harmonics do alter the wave behavior to some extent, they are by themselves not sufficient to explain the transition from small linear oscillations to the large amplitude, broad-band, three-dimensional oscillations characteristic of a fully turbulent boundary layer.
The effect of three-dimensionality on boundary layer transition is then investigated through an analytical and experimental study of single oblique instability waves. This subject has remained largely unexplored, as such disturbances were generally thought to be more stable and therefore less dangerous than their two-dimensional counterparts. Through a series of experiments, however, it is shown that certain conditions exist for which oblique waves are observed to be more unstable than any two-dimensional wave. It is shown that oblique waves exhibit a non-stationary period-doubling behavior that is not seen in two-dimensional disturbances. A vortex pairing mechanism is proposed to explain this behavior, and is shown to occur in a manner consistent with the Biot-Savart law for the induced velocity field.
Denissen, Nicholas Allen. "Roughness-induced Transient Growth: Continuous-spectrum Receptivity and Secondary Instability Analysis." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9192.
Повний текст джерела(8793053), Gregory R. McKiernan. "Instability and Transition on a Sliced Cone with a Finite-Span Compression Ramp at Mach 6." Thesis, 2020.
Знайти повний текст джерела(6196277), Elizabeth Benitez. "Instability Measurements on Two Cone-Cylinder-Flares at Mach 6." Thesis, 2021.
Знайти повний текст джерелаA cone-cylinder-flare geometry was then selected to study the instabilities related to an axisymmetric separation bubble at Mach 6. The sharp cone had a 5-degree half-angle, while flare angles of 10 degrees and 3.5 degrees were tested to compare axisymmetric compression with and without separation, respectively. Under quiet flow, laminar separation and reattachment was confirmed by schlieren and surface pressure-fluctuation measurements. Coherent traveling waves were observed. These were attributed to both the second-mode instability, as well as a shear-generated instability from the separation bubble. The symmetry of the bubble was found to be highly sensitive to angle of attack. Additionally, by introducing controlled disturbances on the cone upstream of the separation, larger-amplitude shear-generated waves were measured while the second-mode amplitudes remained unchanged. Therefore, the shear-generated waves were amplified moving through the shear layer, while the second mode remained neutrally stable. These appear to be the first measurements of traveling waves that are generated in the shear layer of a separation bubble in hypersonic flow.
ZHANG, WEN-ZHENG, and 張文政. "The flow and vortex instability of natural convection boundary layer flow in porus media." Thesis, 1988. http://ndltd.ncl.edu.tw/handle/65032377536121377436.
Повний текст джерелаBergstedt, Josefine. "Cloud Streets. A Study of the Instability Mechanisms Giving Rise to Boundary Layer Rolls." Thesis, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-424449.
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