To be able to harness more power from the wind, wind turbine blades are getting longer. As they get longer, they get more flexible. This creates issues that have until recently not been of concern. Long flexible wind turbine blades can lose their stability to flow induced instabilities such as coupled-mode flutter. This type of flutter occurs when increasing wind speed causes a coupling of a bending and a torsional mode, which create limit cycle oscillations that can lead to blade failure. To be able to make the design of larger blades possible, it is important to be able to predict the critical flutter and post critical flutter behaviors of wind turbine blades. Most numerical research concerning coupled-mode wind turbine is focused on predicting the critical flutter point, and less focused on the post critical behavior. This is because of the mathematical complexities associated with the coupled, nonlinear wind turbine blade systems. Here, a numerical model is presented that predicts the critical flutter velocity and post critical flutter behavior for 3D airfoils with third order structural nonlinearities. The numerical model can account for the attached flow and separated flow region by using the ONERA dynamic stall model. By retaining higher-order structural nonlinearities, lateral and torsional displacements can be predicted, which makes it possible to use this model in the future to control wind turbine blade flutter. Furthermore, by using a dynamic stall model to simulate the flow, the solver is able to predict accurate limit cycle oscillations when the effective angle of attack is larger than the stall angle. The coupled, nonlinear equations of motion are two coupled nonlinear PDEs and are determined using Hamilton’s principle. In order to solve the equations of motion, they are discretized using the Galerkin technique into a set of ODEs. The motion of the airfoil is used as an input to ONERA. The airfoil is sectioned with the lateral position and angle of attack known as well as the velocity and acceleration of the section at an instance of time. This information is used by ONERA to calculate lift and moment coefficients for each section which are then used to calculate the total lift and moment forces of the airfoil. Then, a Fortran code solves the system by using Houbolt’s finite difference method. A theoretical NACA 0012 airfoil has been designed to define the parameters used by the equations of motion. Third bending and first torsional coupling occurs after the critical flutter point and dynamic lift and moment coefficients were observed. Dynamic stall was also observed at wind velocities farther away from the bifurcation point. Bifurcation diagrams, time histories, and phase planes have been created that represent the flutter behavior.

Ce travail porte sur l'étude de la cohérence entre champs triplets générés par interaction non linéaire d'ordre trois. Un protocole indirect, basé sur l'étude du champ issu de la somme de fréquences des champs triplets dans un cristal non linéaire a été envisagé. Une modélisation théorique en formalisme quantique de l'évolution des champs, de leur génération à leur recombinaison, a été développée, donnant lieu à une recherche exhaustive des signatures de corrélations susceptibles d'émerger de notre protocole. Les expériences menées, à savoir la génération non linéaire bi-stimulée et la recombinaison des champs ainsi générés, sont en accord avec notre modèle théorique et permettent de mettre en évidence le masquage des corrélations entre les champs dans ce régime fortement injecté, ces corrélations étant contenues dans les fluctuations quantiques, alors négligeables, des opérateurs champs. Le calcul théorique prédit une signature de corrélations fortes entre les photons triplets dans la cas d'un génération par fluorescence paramétrique, et plus faible dans le cas d'une génération mono-stimulée. / This work deals about the study of coherence between triple photon beams generated by a third order non linear interaction. A protocol, based on the study of the field arising from sum-frequency of the triplet fields in a non linear crystal, was proposed. A theoretical model, in the quantum formalism, was developed, leading to an exhaustive research of the potential signature of the correlations. All the possible schemes were studied : triple fields generation from parametric fluorescence or from stimulated interaction, and recombination of two or three of the triple fields. The experiments we led, i.e. the bi-stimulated non linear generation and the recombination of the so-born fields, agree with our theoretical model and put into light the correlations hiding in this highly stimulated regime, since these correlations lie in the quantum fluctuations of the fields operators. The theoretical calculations predicts a strong correlations signature when the fields are generated from parametric fluorescence, and a weaker one in the case of a generation mono-stimulated.

Depuis plusieurs années, le laboratoire SPCTS de Limoges a focalisé son attention sur l’étude des matériaux tellurates (à base de cations Te6+), dont les propriétés optiques non-linéaires du troisième ordre (χ(3)) doivent être encore supérieures à celles des matériaux tellurites (à base de cations Te4+) traditionnellement considérés. En effet, les calculs ab initio montrent que les propriétés non-linéaires d’ordre trois du composé tellurate TeO3-β sont environ 10 fois plus élevées que celles du composé tellurite TeO2-α. A ce titre, une étude théorique du système (1-x)TeO2+ xTeO3 a été entreprise afin de comprendre l’origine structurale de cette importante différence de propriétés. Les résultats de cette étude ont montré que cette différence était liée à l’augmentation du « degré de polymérisation » et à la diminution du gap énergétique associées à chacune des phases de ce système et ce, avec le taux croissant en cations Te6+. Ces conclusions ont ensuite été généralisées à travers une étude plus globale menée sur un grand nombre de composés oxydes de type MnOm et MnTepOm. Une attention particulière a été portée aux propriétés non-linéaires du composé TeO3-β. Une étude expérimentale puis théorique a permis de mettre en évidence que ses exceptionnelles propriétés non-linéaires étaient directement corrélées aux propriétés des liaisons chimiques le constituant. Compte tenu de l’ensemble de ces résultats, la synthèse de verres tellurates a été envisagée à travers l’étude du système TeO2-Mg3TeO6. Outre leurs forts intérêts pour l’optique, les matériaux tellurates sont aussi de bons candidats en vue d’une intégration dans des dispositifs de type « Low Temperature Cofired Ceramics ». C’est pourquoi, l’étude du composé Bi6Te2O15 a été entreprise. A cet égard, son protocole de frittage a été optimisé au moyen de la technologie « Spark Plasma Sintering » (SPS), et ses propriétés diélectriques mesurées se sont révélées prometteuses. / For several years, SPCTS laboratory of Limoges has focalized his attention to the study of tellurate materials (Te6+ cations-based compounds), whose third order non-linear optical properties (χ(3)) must be superior to those of tellurite materials (Te4+ cations-based compounds) traditionally considered. Indeed, ab initio calculations show those the third order non-linear optical properties of the TeO3-β tellurate compound are about 10 time higher than that of TeO2-α tellurite phase. In this connection, the theoretical study of the (1-x)TeO2+ xTeO3 system was undertaken in order to understand the structural origins of these properties. Results have shown that the increasing of the “polymerization degree” and the decreasing of the energetical gap associated to each structure of this system, with the increasing ratio of Te6+ cations were at the origin of this change of properties. These conclusions were generalized through the study of many oxide compounds such as MnOm and MnTepOm. A special attention was paid to the non-linear properties of the TeO3-β compound. Experimental and theoretical studies allowed highlighting that its exceptional properties were correlated to its chemical bonding properties. Taking into account all these results, the synthesis of tellurate glasses was investigated, through the study of the TeO2-Mg3TeO6 binary system. Besides their great interest for optical applications, tellurate materials are also good candidates for LTCC applications. Therefore the study of the Bi6Te2O15 compound was also managed in this work. Its sintering process was optimized using the “Spark Plasma Sintering” technology, and its dielectric properties measurements have evidenced very promising values.

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