Dissertations / Theses on the topic 'Tourbillon de sillage'
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Sablon, Julien. "Dynamique des tourbillons de sillage stratifiés radialement." Electronic Thesis or Diss., Toulouse, ISAE, 2023. http://www.theses.fr/2023ESAE0070.
The aim of this PhD thesis is to study the stability of a flow representative of trailing vortices generated by aircraft. To this end, two methods of increasing complexity have been used to analyse the stability of the q-vortex model, an approximation of the Batchelor (1964) vortex with the addition of a variable density profile. The first one, the modal linear stability analysis, allows to find the most amplified modes by solving an eigenvalue problem. Given the stationarity and double spatial homogeneity of the base flow field, this method is computationally efficient, allowing a thorough exploration of the problem's parameter space. The second method, the non-modal linear stability analysis, deals with the potential for transient growth mechanisms using a direct-adjoint approach. The use of this methodology is justified by the non-normal character of the Navier–Stokes operator.In the first part, the three-dimensional modal linear stability analysis of the q-vortex is studied. This analysis shows that the vortex stability is substantially modified by the presence of a variable-density profile. When the vortex core is heavier than the external environment, the instability domain, limited to low swirl numbers (q <1.5) in the constant density case, is extended to high swirl numbers. The associated instabilities exhibit high amplification rates and are associated to the Rayleigh–Taylor instability (RTI) mechanism, already identified at infinite swirl numbers for the Lamb–Oseen vortex (Joly et al., 2005). Conversely, the presence of a light core stabilises the flow for large swirl numbers. The effect of the vorticity-to-density radius ratio Ɛ depends on the other parameters. At high Reynolds and swirl numbers, the amplification rate increases continuously with Ɛ. On the other hand, at low swirl numbers (for any Reynolds value) or at high swirl numbers only at low Reynolds, the response to the concentration of the density profile at the centre of the vortex is not monotonic, and there is an optimum value for this ratio close to Ɛ ≈ 2.The second part of the thesis is devoted to the non-modal linear stability analysis of the flow. As this type of analysis had not yet been carried out on a vortex flow with a radial variation of density, the code validation step involved the development of a modal code for determining the adjoint perturbations. These adjoint modes correspond to the optimal excitation leading to maximum energy gain at long times, they are presented briefly. The sensitivity of the optimisation problem to the choice of the energy norm, the initial conditions and the base flow field is studied. Considering the latter, an unsteady modelling of the base flow is conducted via nonlinear simulations initialised from the variable-density q-vortex. At very high Reynolds numbers, viscous diffusion is negligible and the flow can be considered stationary and correctly approximated by the initial analytical solution. However, this is no longer the case at moderate Reynolds numbers, where the base flow becomes unsteady. Approximation via the steady analytical q-vortex-like solution is therefore less suitable for this regime. Finally, the variation of the optimal perturbation at different flow parameters is analysed. In particular, the Orr mechanism for transient energy growth is identified as the main mechanism responsible for the increase in perturbation growth rate at short times
Coppens, Fabien. "Simulations numériques sur le développement de la turbulence dans un tourbillon." Toulouse, INPT, 1998. http://www.theses.fr/1998INPT014H.
Joly, Cécile. "Simulations numériques d'un jet rond turbulent et de son interaction avec un tourbillon de sillage." Université de Marne-la-Vallée, 2002. http://www.theses.fr/2002MARN0147.
The general context of this study concerns the impact of contrails, these famous white plumes frequently observed in the aircraft wake, on the atmosphere. From an aerodynamic point of view, the formation of the contrails is characterised by the interaction between a turbulent jet and a wing-tip vortex. The aim of this thesis is to contribute to a better understanding of the thermal and dynamic phenomena involved in this flow. This work is based on the numerical resolution of the three-dimensional, unsteady and compressible Navier-Stokes and energy conservation equations. Two approaches are considered: the direct numerical simulation and the large eddy simulation. A temporal simulation of the transition to turbulence of a non-isothermal jet is performed without accounting for the vortex flow field. A the end of this simulation, a vortex model is superimposed on the jet flow field. The first part of this thesis describes the two approaches, the different subgrid models chosen for the large eddy simulations, and the numerical techniques employed. The second part is devoted to the jet flow simulation, and here the objective is to determine the subgrid model appropriated to this flow configuration. The third part is dedicated to the simulation of interaction between the jet and the vortex. Results are compared to experimental data. The simulations have demonstrated the development of large scale structures all around the vortex core. The temperature field concentrates in the large scale structures
Nybelen, Laurent. "Etude numérique d'écoulements tourbillonnaires de sillage d'avion." Phd thesis, Université Paul Sabatier - Toulouse III, 2008. http://tel.archives-ouvertes.fr/tel-00450477.
Thomas, Olivier. "Simulations numériques de perturbations d’un tourbillon de Lamb-Oseen : application à l’éclatement tourbillonnaire dans les sillages des avions de transport." Paris 6, 2009. https://tel.archives-ouvertes.fr/tel-00814536.
This report synthesizes the works performed on the theme of end effects and vortex bursting observed in experimental facilities such as catapult wind tunnels or towing tanks, whose aim it is to characterize the wake vortices of civil aircraft. It includes a bibliographical synthesis, the post-processing of experimental campaigns performed in the B20 wind tunnel in ONERA Lille, the presentation of the Direct Numerical Simulation FLUDILES code, the modelling of the disturbances of a Lamb-Oseen vortex and the confirmation of DNS calculations upon the linear stability theory, the numerical and theoretical study of the nonlinear dynamics of a Lamb-Oseen vortex by means of DNS
Thomas, Olivier. "Simulations numériques de perturbations d'un tourbillon de Lamb-Oseen : application à l'éclatement tourbillonnaire dans les sillages des avions de transport." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00814536.
Bolnot, Hadrien. "Instabilités des tourbillons hélicoïdaux : application au sillage des rotors." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4825/document.
This thesis is devoted to the stability properties of helical vortices, which are of interest for applications such as helicopter and wind turbine wakes.In a first part, the spatio-temporal development of the pairing instability is characterised for an infinite array of vortex rings, using a pseudo-spectral numerical code. We show that this axisymmetric flow model is indeed a good approximation of the helical system in the limit of large helix radius and small pitch. Under these assumptions, and by using appropriate dimensionless variables, we also show that the theoretical result concerning the spatio-temporal growth rate for a double row of point vortices represents a good prediction for the helical case.In a second part, we describe how one or several helical vortices were generated in a carefully controlled way using small-scale rotor models in the water channel of the laboratory. Introducing perturbations with well-defined amplitudes and frequencies, the growth rate of the pairing instability could be measured experimentally and compared to theoretical predictions. The non-linear evolution of these perturbations, as well as other unstable modes of smaller wavelengths, were also observed experimentally for the first time.Finally, these results were applied to helicopter wakes for the prediction of the Vortex Ring State (VRS) regime and to the transition to turbulence in wind turbine wakes
Riera, William. "Evaluation of the ZDES method on an axial compressor : analysis of the effects of upstream wake and throttle on the tip-leakage flow." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0030/document.
The tip-leakage flow in axial compressors is studied with the Zonal Detached Eddy Simulation (ZDES). This study aims at evaluating the capability of hybrid URANS/LES methods to simulate the tip-leakage flow within a realistic axial compressor in order to better understand the involved physics, especially the behaviour of the flow near surge and the effects of stator wakes on the downstream rotor. Once the ZDES method is chosen, a numerical test bench is defined to simulate the first rotor of the research compressor CREATE. This bench takes into account the unsteady effects of the Inlet Guide Vane (IGV), such as its wake as well as vortices generated at the IGV hub and tip. It is based upon ZDES meshing criteria and is used to evaluate this method compared to classic RANS and URANS approaches. A method validation is carried out up to a spectral analysis compared to experimental data. The ZDES is capable to capture more accurately the intensity and position of the unsteady phenomena encountered in the tip region, especially the tip-leakage vortex. The power spectral densities highlight that this partly originates from a better capture of the energy transfer from large to small structures until their dissipation. The discrepancy between the methods is accentuated as the tip-leakage vortex crosses the shock. Near the surge line, the interactions between the shock, the tip-leakage vortex, the boundary layer developing on the shroud and the vortex generated by the IGV tip are amplified. The boundary layer on the shroud separates earlier and a local flow inversion occurs. Besides, the tip-leakage vortex widens and is deflected toward the adjacent blade. This strengthens the double leakage. At the design operating point, the interaction of the IGV tip vortex with the shock and the rotor tip vortex is studied. A vortex flutter is observed as the IGV tip vortex arrives on the rotor blade and stretches the rotor tip vortex. This phenomenon decreases the double leakage
Moet, Henri. "Simulation numérique du comportement des tourbillons de sillage dans l'atmosphère." Toulouse, INPT, 2003. http://www.theses.fr/2003INPT007H.
Meunier, Patrice. "Tourbilons et sillages dans les fluides géophysiques." Habilitation à diriger des recherches, Université de Provence - Aix-Marseille I, 2009. http://tel.archives-ouvertes.fr/tel-00426779.
Rivoalen, Elie. "Étude numérique et expérimentale de tourbillons de sillage proches d'une surface libre." Le Havre, 1994. http://www.theses.fr/1994LEHA0007.
Liu, Zhongxun. "Modélisation des signatures radar des tourbillons de sillage par temps de pluie." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0015/document.
Nvestigation on radar monitoring of wake vortices in rainy weather is of both scientific and practical interests. This topic hasbeen tackled through three successive steps during this thesis.Firstly, the motion of raindrops in wake vortices has been modeled and simulated. The equation of the motion has been derived and the methodology to compute the raindrops' trajectory and distribution in the flow induced by the wakevortices has been proposed. Secondly, two simulators have been developed for evaluating the radar signatures of raindropsin wake vortices. Those simulators have been used to reproduce experimental configurations and the comparison betweenmeasured and simulated signature has shown an interesting agreement at X and W band. Lastly, the interpretation of radarsignatures of raindrops in wake vortices has been presented. The dependence of radar signatures on rain rate, vortexcirculation and radar parameters has been studied. A wake vortex detection method based on the analysis of Dopplerspectrum width of raindrops and a methodology to estimate the wake vortex characteristics have been proposed.The radar signatures of wake vortices in rainy weather have been modeled and analyzed in this thesis. The simulationresults have demonstrated the capability of radar to detect wake vortex in rainy weather. The methodologies developed inthis thesis can be further exploited for designing new wake vortex radar systems
Fabre, David. "Instabilité et instationnarités dans les tourbillons : Application aux sillages d'avions." Paris 6, 2002. http://www.theses.fr/2002PA066520.
The trailing wake generated by an aircraft is composed of persistant vortices wich pose a danger to following aircrafts. This thesis is concerned with the instabilité and instationaritymechanisms characterising these vortices. Emphasis is laid on the properties of realistic trailingwakes and the possible contribution of these mechanisms to wake dissipation. The first part of the thesis is devoted the properties of trailing wakes, and is based on analyses of wind tunnel experiments. Several "realistic" vortex models are described. In the second part the linear mechanisms affecting an isolated vortex are studied using a spectral collocation method. The Kelvin waves (or inertial waves) are first cconsidered, and it is shown that in "realistic" vortices most of these waves become damped. The properties of the short-wave Widnall instabilities are then described for the same "realistic vortices. A family of viscous instabilities existing in high-Reynolds vortices in the presence of axial flow is then considered. In a third part the long-wave cooperative instabilities in systems of parallel vortices are studied using a vortex filament method. The case of two vortices is first considered ; counter-rotating pairs are affected by the long-wave Crow instability while corotating pairs are stable. The stability of an aircraft wake model composed of two pairs is then considered. An optimal perturbation analysis is used and allows to emphasize the interest of counter-rotating configuration and the necessity of a long wavelength forcing in order to achieve a rapid wake dissipation. In the fourth part the Crow and Widnall insatbilities are reconsidered in the framework of spatial theory, and the convective or absolute nature of these instabilities are evaluated
Fabre, David. "Instabilités et instationnarités dans les tourbillons : application aux sillages d'avions /." [Châtillon] : ONERA, 2002. http://catalogue.bnf.fr/ark:/12148/cb38839378d.
Laporte, Florent. "Simulation numérique appliquée à la caractérisation et aux instabilités des tourbillons de sillage d'avions de transport." Toulouse, INPT, 2002. http://www.theses.fr/2002INPT003H.
Ali, Mohamed. "Caractérisation et instabilités des tourbillons hélicoïdaux dans les sillages des rotors." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4708/document.
This present work is aimed to study helical vortices encountered in the wakes of rotating elements. For this, the generation of a helical wake of a one-bladed-rotor in a laminar velocity field, is simulated by the actuator line method. This method is a coupling of a Navier-Stokes (NS) solver with the Actuator Line Method where the blade is replaced by the body forces. This method has been implemented in a finite difference code, that we have written in parallel to solve the 3D incompressible NS equations written in cylindrical coordinates. The order of accuracy of the method is two both in time and space. The NS solver was validated comparing growth rates of an unstable jet, found numerically, and those of linear instability theory. A good agreement was found. A good agreement was also found comparing numerical results to analytical formulations and experimental data. It was shown that the method predicts well the blade aerodynamics . Then, the helical tip vortex is characterized for different Reynolds numbers and Tip Speed Ratios. The vorticity and the azimuthal velocity were found self-similar and the vortex core follows asymptotically the linear 2D diffusion law. A simple model for the helical vortex core was proposed. The presence of an axial velocity inside the vortex core was highlighted. Then, a stability study of the helical tip vortex was done using an angular velocity dependent on time to perturb the flow. The largest growth rates were found in good agreement with those of the (2D) pairing instability. Three types of modes were identified based on the perturbation frequency. The results are similar to those found in previous analytical and experimental works
Duplantier, Stéphane. "Etude expérimentale d'un sillage confiné se développant en aval d'un corps d'arrêt : influence de la combustion sur la structure du sillage." Poitiers, 1995. http://www.theses.fr/1995POIT2323.
Belahadji, Brahim. "Cavitation dans le sillage turbulent d'un obstacle." Université Joseph Fourier (Grenoble), 1993. http://www.theses.fr/1993GRE10101.
Puel, Florent. "Intéraction de tourbillons avec une paroi." École nationale supérieure de l'aéronautique et de l'espace (Toulouse ; 1972-2007), 1999. http://www.theses.fr/1999ESAE0005.
Moldoveanu, Cristian-Emil Boisson Henri-Claude Moraru Florentin. "Simulation aux Grandes Échelles de tourbillons longitudinaux soumis à une turbulence extérieure intense." Toulouse : INP Toulouse, 2008. http://ethesis.inp-toulouse.fr/archive/00000696.
Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. 120 réf.
Bouchet, Eric. "Étude du bruit d'interaction pale-sillage d'un rotor principal d'hélicoptère." Le Havre, 2002. http://www.theses.fr/2002LEHA0011.
Understanding the mecanisms responsible for the BWI noise of helicopter main rotor which occures during perpendicular blade-vortex interaction. An extensive analysis of the blade pressure is performed to get a deeper insight of the BWI mecanism. A stability analysis of modelization of the incident flow (two rectilinear and parallel filaments) is undertaken. The numerical and theoritical results are found to be in good agreement and consistent with the proposed instability hypothesis
Chkir, Saïd. "Contribution àl'étude aérodynamique d'une éolienne par une méthode de sillage libre." Paris, ENSAM, 2010. http://www.theses.fr/2010ENAM0025.
This thesis presents a method for calculating the unsteady three-dimensional flow around a wind turbine rotor. The real flow is replaced by a free stream past a vortex model of the rotor. This model consists of lifting vortex lines which replace the blades and a trailing free vorticity. For simplicity the vorticity shed from the blade trailing edge is concentrated in two vortices issued from tip and root. To compute the resulting flow and to evaluate the unsteady forces exerted on the rotor, a free wake method is used. This method consists of a Lagrangian representation of the flow field. The evolution of the wake downstream of the rotor is obtained by tracking the markers representing the vortices issued from the blade tips and roots. To solve the wake governing equation and to obtain the marker positions, a time-marching method is applied and the solution is obtained by a second order predictor-corrector scheme. The free wake methods are usually inviscid, but in the present approach, the viscous effects are taken into account. It is supposed that the induced velocity on vortex line is limited by a maximum velocity in the viscous vortex core. The diffusion of the vortex lines and the vortex core growth are supposed to depend on vortex age. All constants needed to represent the viscosity effects are extracted from experiments. To validate the proposed method a comparison is made with experimental data obtained in the case of a model of wind turbine where the flow field immediately behind the rotor is measured by means of particle image velocimetry (PIV). It is shown that the numerical simulation captures correctly the near wake development
Ahd, Mohamed. "Etude expérimentale du développement du sillage d'un cylindre circulaire placé en amont d'un corps d'arrêt." Poitiers, 1994. http://www.theses.fr/1994POIT2294.
Tschümperlé, Denis. "Étude numérique de l'interaction tourbillons-onde acoustique." Le Havre, 2000. http://www.theses.fr/2000LEHA0002.
De, Souza Fenella. "Etude expérimentale de l'interaction sillage/paroi dans une couche limite turbulente manipulée par un cylindre circulaire." Poitiers, 1996. http://www.theses.fr/1996POIT2388.
Leweke, Thomas. "Etude expérimentale et modélisation du sillage d'un tore à bas nombre de Reynolds." Aix-Marseille 1, 1994. http://www.theses.fr/1994AIX11028.
Berenger, Thierry. "Contribution à l'étude expérimentale et numérique du sillage tourbillonnaire d'un rotor d'hélicoptère en vol d'avancement." Aix-Marseille 2, 1994. http://www.theses.fr/1994AIX22092.
Bonnier, Marion. "Sillage d'une sphère en milieu linéairement stratifié : caractérisation des structures tourbillonaires." Toulouse, INPT, 1999. http://www.theses.fr/1999INPT023H.
Cruz, Marquez Rolando. "Impact du chargement alaire sur les propriétés et la dynamique des tourbillons de sillage, une analyse en bassin hydrodynamique." Electronic Thesis or Diss., Centrale Lille Institut, 2023. http://www.theses.fr/2023CLIL0037.
The impact that span-wise shape modifications on a wing haveon the dynamics of trailing vortices is studied using towing tank experiments. The focusis on understanding if wake hazard can be reduced through intelligent wing design. Thebaseline wing is rectangular, variations in wing-loading configurations are then examined,including high-lift loading, trailing edge disturbances and wings that generate multiple vor-tices. Stereo PIV measurements track vortex wake development from the roll-up stage up to300 spans downstream. The mean chord-based Reynolds number is Rec = 105.The essential properties of the vortices are presented and analyzed to provide physicalmeaning. Trailing edge shape modifications result in enlarged trailing vortices with con-sistent circulation. High-lift wing-load configurations, generating co-rotating vortex pairs,show a fusion phenomenon and a subsequent diffusive effect on the fused vortex core com-pared to the baseline. An increase in circulation,up to 20%, is observed due to closer vortexproximity. Conversely, configurations with counter-rotating vortices exhibit a viscous diffu-sion process, reducing the circulation of the wing-tip vortex.Overall, the present work shows that wing loading has an important impact on the spe-cific position, strength and size of vortices in the wake
Santa, Cruz Bustamante Alina. "Contrôle par plaque séparatrice du proche sillage à l'aval d'un cylindre semi-circulaire." Poitiers, 2001. http://www.theses.fr/2001POIT2293.
Brunet, Stéphane. "Etude numérique et expérimentale du mélange des jets de moteurs dans les tourbillons de sillage d'un avion de ligne." Aix-Marseille 1, 1999. http://www.theses.fr/1999AIX11048.
Jaouani, Nassim. "Modelling of installation effects on the tonal noise radiated by counter-rotating open rotors." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC002.
Les hélices contrarotatives constituent une alternative possible aux turboréacteurs pour les avions moyens- courriers. Réduisant significativement la consommation de carburant et les émissions de gaz à effet de serre, ils peuvent néanmoins conduire à un rayonnement sonore accru de par l'absence de carénage. Prédire correctement le rayonnement sonore de telles motorisations est donc indispensable pour réduire les mécanismes sources propres au moteur isolé ou assurer une solution d'installation acoustique optimale. Un tel objectif est abordé dans cette thèse en deux temps. Dans un premier temps, l’étude vise à prédire le bruit tonal rayonné par la première hélice d'un moteur monté à l'arrière du fuselage (configuration dite en pousseur), en considérant les effets du sillage du pylône supportant le moteur et de l'écoulement moyen. Partant du formalisme de Ffowcs Williams & Hawkings, trois sources sonores sont identifiées à cet effet. La charge instationnaire, tout d'abord, est calculée en s'appuyant sur une méthodologie similaire à celle utilisée pour la prédiction du bruit d'interaction de sillages entre les deux rotors. Le déficit de vitesse dans le sillage du mât est décomposé localement en rafales bidimensionnelles dans un repère attaché au rotor amont. La portance instationnaire induite par chaque rafale sur un segment de pale est calculée en utilisant une fonction de réponse analytique linéarisée considérant une géométrie réaliste. Deuxième contribution, la charge stationnaire est évaluée au moyen d'un logiciel s'appuyant sur la théorie de la ligne portante mais également via des simulations numériques pour différentes surfaces sources de référence. Enfin, le bruit d'épaisseur associé au déplacement du volume de la pale est inclus dans l'analyse à partir de la formulation d'Isom. D'après les hypothèses de l'acoustique linéaire, toutes ces sources modélisées comme des dipôles acoustiques tournant dans une atmosphère uniforme en mouvement sont ensuite sommées pour calculer le bruit en champ lointain. L'ensemble de la méthodologie est comparé à des données d'essai et des prédictions d'un logiciel de référence. Une étude paramétrique considérant plusieurs positionnements du pylône et des configurations avec soufflage est effectuée afin de bien mettre en évidence les contributions relatives des trois sources sonores. Dans un deuxième temps, le bruit d'interaction de sillages étant reconnu comme la contribution majoritaire en configuration isolée, sa modélisation est complétée en introduisant la dynamique du tourbillon se développant au voisinage du bord d'attaque du rotor aval. Une méthodologie semi-analytique est développée pour déterminer un tourbillon attaché au-dessus d'une plaque plane plongée dans un écoulement uniforme avec incidence. Appliquée au cas d'une pale aval traversant le sillage du rotor amont, elle fournit une première estimation de la contribution sonore du tourbillon
Hallermeyer, Alexandre. "Traitement du Signal d’un LIDAR Doppler scannant dédié à la surveillance aéroportuaire." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC007/document.
An algorithm was developed to estimate precisely wake vortices parameters (positions and circulations) using spectral data provided by a LIDAR. It is articulated in 3 main stages: The first one allows to detect the presence of vortices and to make a rough localization thanks to the method of the velocity envelopes. The second step is to refine the estimation of vortex positions using an optimization of the least squares criterion. This step also permits to make an first estimation of the vortices circulation. The third and final step focuses on estimating vortex circulations by maximizing the likelihood criterion. Estimates are becoming finer and more focused on the most critical parameters. The development of this algorithm required the use of several models (LIDAR, wake vortices, atmosphere) and to formulate a number of simplifying assumptions in order to reach a reasonable computational cost. The proposed algorithm was then subjected to a performance evaluation, the interest being focused on the robustness with respect to the different noises altering the measurement, particularly the one related to the atmospheric turbulence, and with respect to the model errors. This evaluation was carried out both on simulated data using simplified parametric models, and on Large Eddy Simulations.The instrumental parameters of LIDAR are potential degrees of freedom to improve the performance of the estimator, in particular for the most critical quantities, that is to say the circulation values. The calculation of the performance of the estimator requiring a significant computational cost, it lends itself poorly for optimization purposes. This is why a study of the influence of the LIDAR parameters on the Cramér-Rao Bound (CRB) was carried out. This study allowed to understand the influence of the instrumental parameters and to reach an optimal configuration for the CRB
Moldoveanu, Cristian-Emil. "Simulation aux Grandes Échelles de tourbillons longitudinaux soumis à une turbulence extérieure intense." Toulouse, INPT, 2007. http://ethesis.inp-toulouse.fr/archive/00000696/.
The aim of this thesis is to study the behavior of the vortices under the influence of an external turbulence. We present the main mechanisms of instability, which is the basis of the counter-rotating vortices longitudinal decay. For the simulations we have selected the software JADIM developed by IMFT, adapted for Large Eddy Simulation of the turbulent flows. The validation of the numerical methods and of the software used, is made by comparing the theoretical and the numerical results of a single longitudinal vortex flow, in absence of external disturbances. We studied the behavior of a perturbed flow to the interior or to the exterior of a vortex. The study of the effect of the external turbulence on a counter-rotating longitudinal vortices pair highlighted the competition between elliptical and Crow instability. The simulation of the vortices pair in ground effect highlighted the generation mechanism of a vorticity layer and the generation of the secondary vortices
Michaux-Leblond, Nathalie. "Étude du comportement dynamique du sillage à l'aval d'un cylindre chauffé en régime mixte." Le Havre, 1994. http://www.theses.fr/1994LEHA0006.
Rehimi, Férid. "Caractérisation expérimentale des structures tourbillonnaires derrière un cylindre en milieu confiné par la PIV et la polarographie." Nantes, 2006. http://www.theses.fr/2006NANT2023.
This work deals with the experimental characterization of the vortex shedding from a circular cylinder between parallel walls. Two experimental measurement techniques were used for the investigation of the wake downstream the cylinder : the PIV (Images Particles Velocimetry) and the polarographic method, with circular probes mounted flush on one of the two parallel walls of the channel downstream from the obstacle. In parallel to this work, one developed a computational code for the inversion of the convection-diffusion equation, which is based on the sequential Beck algorithm, in order to determine the wall shear stress from the limiting current delivered by the probes. Its validation was carried out beforehand by measurements in a cone-plate rheometer. Thereafter, one studied the vortex shedding behind the circular cylinder by synchronized measurements between PIV and polarography. Measurements of PIV were used to characterize the various flow regimes, and to show the main differences between this case of the confined wake (for a blockage ratio of 1/3) and the case of the non-confined wake. Then, one studied the dynamic of vortex structures downstream the cylinder. The decomposition of the instantaneous velocity fields obtained by PIV in Proper Orthogonal Modes (POD) made it possible to follow their energetic distribution for the studied range of Reynolds numbers ( 50 ≤ Re ≤ 300 ). With this decomposition, it is possible to make an inhomogeneous filtering and to reconstitute filtered fields solved in time. Finally, a comparison between the results of PIV and of electrochemistry was carried out
Brajon-Socolescu, Laura. "Étude numérique de l'instabilité de Bénard - Von Karman derrière un cylindre chauffé." Le Havre, 1996. http://www.theses.fr/1996LEHA0005.
Michea, Bertrand. "Etude des sillages de rotors d'helicoptere en vol d'avancement et de leur influence sur les performances du rotor (interaction pale-tourbillon)." Paris 6, 1992. http://www.theses.fr/1992PA066255.
Jugier, Rémi. "Stabilité bidimensionnelle de modèles de sillage d’aéronefs." Thesis, Toulouse, ISAE, 2016. http://www.theses.fr/2016ESAE0021/document.
Aircraft wake vortex control allows for reducing of their dangerousness and consequently improve airport take-off / landing requencies. Contrails and artificial cirrus clouds formation could also be influenced through this control of wake vortices and allow for reducing of terrestrial radiative forcing generated by aviation. Brion (2014) have shown by a modal stability analysis that the Lamb-Chaplygin dipole, often used as a far-field model for aircraft wake vortices, is unstable to two-dimensional perturbations at Iow Reynolds numbers. We first extend this twodimensional modal stability analysis to more realistic dipole models, for a Wide range of aspect ratios, and obtain, for Iow Reynolds numbers, instabilities of the same nature (displacement modes) as for the Lamb-Chaplygin dipole. However, we show that the growth of those modes depends greatly on the dipole aspect ratio, and that this growth is greatly diminished hen the dipole diffusion is taken into account. We then study two-dimensional transient growth for far-field models (dipoles) and near-field models (vorticity sheets), in homogeneous and stratified atmospheres. ln all cases, optimal perturbations are vorticity spirals oriented against shear and located at the periphery of the vortices, which eventually lead to development of the instabilities described in the modal analysis through a contamination mechanism of the vortex cores, initially identified by Antkowiak & Brancher (2004) for an isolated vortex
Hoinville, Eric. "Etude du sillage de rotors d'hélicoptère en configuration de Vortex Ring." Phd thesis, Orléans, 2007. http://www.theses.fr/2007ORLE2070.
Bouchet, Jean-Paul. "Etude de l'influence d'un jet pariétal sur les mécanismes de déposition en paroi de culot ; application à l'encrassement des véhicules automobiles." Poitiers, 1999. http://www.theses.fr/1999POIT2319.
Perrin, Rodolphe Braza Marianna. "Analyse physique et modélisation d'écoulements incompressibles instationnaires turbulents autour d'un cylindre circulaire à grand nombre de Reynolds." Toulouse : INP Toulouse, 2006. http://ethesis.inp-toulouse.fr/archive/00000120.
Hamma, Laurence. "Etude de la diffusion de la chaleur en aval d'un cylindre chauffé à faible nombre de Reynolds (40." Rouen, 1988. http://www.theses.fr/1988ROUES031.
Jermann, Cyril. "Eclatement tourbillonnaire dans le sillage turbulent d'un véhicule générique." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4340/document.
This thesis is a contribution to the study of the longitudinal vortices developing in the near wake of ground vehicles, with the general purpose of reducing the aerodynamic drag by triggering the vortex breakdown phenomenon. We present a new data acquisition system called A-SPIV, allowing to reconstruct a 3D turbulent time-averaged velocity field from stereo-PIV planes measured by translation of the whole cameras-laser system, with no need to recalibrate. We also propose a method to reconstruct the mean pressure in the bulk from the A-SPIV data and from a dedicated wall static pressure measurement. This new overall experimental protocol is applied to a standard aerodynamic test-case, the 25° Ahmed body, all results being compared and validated at high turbulent Reynolds number against existing data from the literature. A thorough analysis of the longitudinal vortices suggests the occurrence of a spontaneous vortex breakdown in the near-wake, although there exist no stagnation point in the experimental data. Such vortex breakdown is therefore evidenced using two different theoretical criteria considering the phenomenon as the consequence of either a reorganization of the vorticity, or an accumulation of inertial waves propagating along the vortex core. The underlying analyses are carried out in a cylindrical system attached to the vortex axis and predict a single breakdown position, in good agreement with the singular position initially inferred from the A-SPIV data. The thesis ends with a global stability analysis of the turbulent mean flow suggesting a possible connection between the occurrence of vortex breakdown and a global instability of the longitudinal vortex
Johnson, Holly. "Nonlinear dynamics of wake vortices." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX101/document.
Aircraft wakes have been the subject of extensive research for several decades as it poses economic, safety and environmental issues. The wake is composed of powerful counter-rotating vortices that persist long after the aircraft has passed. In this thesis, the nonlinear dynamics of aircraft wake vortices is investigated through Direct Numerical Simulation. The aim is to explore the nonlinear effects on wake vortex behaviour and evaluate the potential for the anticipated destruction of the vortices through optimal perturbation. First the disruptive potential of the linear optimal perturbation of the flow is evaluated by applying it with increasing initial amplitude and observing the nonlinear response of the flow. With sufficient yet reasonable initial amplitude the linear optimal perturbation halves the life-span of the vortex pair by accelerating the loss of coherence of the vortices after the linking phase. Next the nonlinear gradient-based optimisation tool that was developed during the thesis is validated by reproducing existing results concerning a simple vortical flow: an isolated two-dimensional vortex. In doing so new nonlinear optimisation results are obtained and analysed. In particular it is shown that the 2D nonlinear optimal perturbation of an isolated vortex can induce considerably greater transient growth than the linear optimal. In some cases the nonlinear optimal causes a transition to a quasisteady asymmetric state, bypassing the natural axisymmetrisation process. The effect of the vortex vorticity profile on the optimal perturbations is also studied. Vortices with sharper profiles experiencefar greater linear perturbation growth, however the nonlinear growth is significantly inferior. Finally the nonlinear optimal perturbation analysis of the isolated vortex is extended to three dimensions. Although the 3D nonlinear optimals produce less growth than their linear counterparts, they can lead to quasi-permanent high energy states
Parezanovic, Vladimir. "Experimental study of the sensitivity of global properties of turbulent bluff body wakes using steady disturbance methods." Palaiseau, Ecole polytechnique, 2011. https://theses.hal.science/index.php?halsid=uofsba7dj5fa0catc3i9mh00v0&view_this_doc=tel-00670537&version=1.
The sensitivity of the global properties of a turbulent wake behind a D-shaped bluff cylinder is investigated experimentally by introducing a much smaller control cylinder of various shapes and diameters as a local disturbance. Hot-wire anemometry and particle image velocimetry are used to obtain local and global measurements of the turbulent wake. Aerodynamic forces acting on the main cylinder are derived from pressure measurements around its perimeter. The results are presented in the form of sensitivity maps of the Strouhal number and base pressure. The sensitivity of global properties is interpreted on the basis of the ability of the control cylinder to change the size of the formation region of the Kármán vortex street mainly through the turbulent properties modification of the perturbed detached shear layer. The corresponding physical mechanisms are discussed with regard to the origins of drag reduction and global frequency modification. The impact of the perturbation on the 3D properties of the wake is investigated through two-point velocity correlation and wake visualization. Bi-stable flow configurations for some positions of the control cylinder are examined
Merle, Axel Legendre Dominique. "Intéraction d'une bulle sphérique avec un écoulement turbulent ou tourbillonnaire." Toulouse : INP Toulouse, 2005. http://ethesis.inp-toulouse.fr/archive/00000088.
Laurent, Jacques. "Contribution a l'etude des ecoulements tridimensionnels decolles a grand nombre de reynolds." Paris 6, 1988. http://www.theses.fr/1988PA066348.
Gosse, Kevin. "Etude expérimentale de la dispersion d'un scalaire passif dans le proche sillage d'un corps d'Ahmed." Phd thesis, Université de Rouen, 2005. http://tel.archives-ouvertes.fr/tel-00012128.
Les caractéristiques des champs de vitesse mesurées pour les trois angles d'inclinaison a ont montré que le champ dynamique dans le sillage proche dépend très fortement de cet angle lorsque le nombre de Reynolds augmente. Ces mesures ont mis en évidence pour a=25° l'existence d'une transition 2D-3D à un nombre de Reynolds ReLc=2,7.104. L'étude des champs thermiques a mis en évidence une complexité importante liée à la fois au caractère complexe du champ dynamique et à l'injection décentrée. Nous avons décrit les différents scénarios de transport et de mélange du scalaire en fonction de l'angle a de la lunette arrière. Le problème du mélange a été abordé en étudiant successivement les variations de l'écart de la température moyenne maximale, de l'intensité maximale des fluctuations de température et du taux de dissipation de ces fluctuations. Les résultats obtenus dans cette étude ont permis de déterminer le temps de mélange et d'estimer les ordres de grandeur des concentrations de polluants émises reçues par des récepteurs particuliers (piéton au bord d'une route lors du passage d'un véhicule automobile ou automobiliste dans le sillage d'une voiture).
Gosse, Kévin. "Etude expérimentale de la dispersion d'un scalaire passif dans le proche sillage d'un corps d'Ahmed." Rouen, 2005. http://www.theses.fr/2005ROUES044.
This experimental work concerns the diffusion of heat downstream of a point source located at the Ahmed body base for slant angles " of 5°, 25° or 40°. This study has been carried out in air and in water at different Reynolds numbers. Laser Doppler velocimetry (LDV), hot wire anemometry and cold wire thermometry have been used to measure velocity and temperature in the near wake ( ). Characteristics of the velocity fields have been found to be strongly dependent on " when the Reynolds number increase. For "=25°, temperature and velocity measurements show in evidence the existence of a transition 2D-3D at a Reynolds number ReLc=2,7. 104. Thermal fields revealed a high degree of complexity linked both to the complex nature of the dynamic field and the off axis location of injection. Scalar transport and mixing are analysed as a function of the rear slant angle ". The mixing problem has been studied by considering successively variations of maximum values of temperature excess, maximum intensity of the temperature variance and dissipation rate of temperature variance. These results allowed to determine the mixing time and to estimate the pollutant concentrations received by particular receptors (pedestrian close to a road or car driver)