Magneto-Mechanical MicroSystems (MMMS) for active flow control.
Microsystèmes Magnéto-Mécaniques (MMMS) pour le contrôle actif d'écoulements aérauliques.
Résumé
Situated at the intersection between the needs of the Aerospace industry and the possibilities of the MEMS community, the thesis dealt with the dimensioning, realization and characterization of flexible membrane microvalves producing pulsed jets for active flow control on one hand, and of integrated magnetostrictively actuated microactuators on the other hand. This work was supported by the CNRS; by both DASSAULT AVIATION and MBDA, and is part of the ADVACT European project.
A preliminary study of the physics of flow control and of the industrial needs in such a domain yield the definition of precise specifications for the management of detached flows in the case of aeronautical applications. Two characterization benches were subsequently built in order to measure the properties of millimetre sized pulsed jets by high speed shadowgraph and hot wire anemometry.
The microvalve, witch actuation principle is based on the pinching of a micofluidic channel by a flexible membrane was designed, fabricated and characterized. A theoretical study of the static and dynamical characteristics of the fluid-structure coupled system yield the identification of three actuation means and their characteristic bandwidth: electromagnetic actuation (0-600 Hz), assisted self-oscillation (400-1500Hz), and self-oscillation (1kHz – 2.5 KHz). The fabricated prototypes show an outlet speed superior to 100 m/s in each of these frequency ranges. A numerical simulation study was then undertaken in order to maximize the outlet speed via the optimization of the microchannel geometry. Microvalve arrays were finally packaged and installed in wind tunnel for further research on detached flows (ONERA).
An innovative microsystem design consisting in a cantilever covered with a nanostructured magnetostrictive film actuated in situ by two microcoils was also investigated. Using the huge sensitivity gain obtained by the induction of a magnetic instability in the magnetostrictive film (Spin Reorientation Transition, SRT), the magnetic field produced by two microcoils placed at each tip of the cantilever was shown sufficient to induce the vibration of the mechanical part. Moreover, such a system benefits from the highly non-linear properties of the magnetostrictive films near the SRT. A microvalve concept based on this type of actuation was finally proposed and fabricated.
A preliminary study of the physics of flow control and of the industrial needs in such a domain yield the definition of precise specifications for the management of detached flows in the case of aeronautical applications. Two characterization benches were subsequently built in order to measure the properties of millimetre sized pulsed jets by high speed shadowgraph and hot wire anemometry.
The microvalve, witch actuation principle is based on the pinching of a micofluidic channel by a flexible membrane was designed, fabricated and characterized. A theoretical study of the static and dynamical characteristics of the fluid-structure coupled system yield the identification of three actuation means and their characteristic bandwidth: electromagnetic actuation (0-600 Hz), assisted self-oscillation (400-1500Hz), and self-oscillation (1kHz – 2.5 KHz). The fabricated prototypes show an outlet speed superior to 100 m/s in each of these frequency ranges. A numerical simulation study was then undertaken in order to maximize the outlet speed via the optimization of the microchannel geometry. Microvalve arrays were finally packaged and installed in wind tunnel for further research on detached flows (ONERA).
An innovative microsystem design consisting in a cantilever covered with a nanostructured magnetostrictive film actuated in situ by two microcoils was also investigated. Using the huge sensitivity gain obtained by the induction of a magnetic instability in the magnetostrictive film (Spin Reorientation Transition, SRT), the magnetic field produced by two microcoils placed at each tip of the cantilever was shown sufficient to induce the vibration of the mechanical part. Moreover, such a system benefits from the highly non-linear properties of the magnetostrictive films near the SRT. A microvalve concept based on this type of actuation was finally proposed and fabricated.
Situé à l'intersection des besoins de l'industrie aéronautique et des possibilités offertes par les microtechnologies, le travail présenté dans ce mémoire concerne le dimensionnement, la réalisation et la caractérisation de micro-actionneurs à membrane souple permettant la fabrication de micro-jets pulsés pour le contrôle actif de décollement d'une part, et de micro-actionneurs à actionnement magnétostrictif intégré d'autre part. Ainsi, un cahier des charges précis est a d'abord été défini suite à l'analyse des phénomènes fluides liés au contrôle de décollement et à l'identification des besoins industriels dans ce domaine. Deux bancs de mesure ont ensuite été mis en place de manière à permettre la caractérisation complète des microjets pulsés, par ombroscopie ultra-rapide et anémométrie au fil chaud. Un prototype de microvalve dont le fonctionnement est fondé sur le pincement d'un canal microfluidique à l'aide d'une membrane souple a été dimensionné puis fabriqué. Une étude théorique du fonctionnement statique et dynamique du système couplé fluide-structure a permis d'identifier trois types d'actionnement et leur plage fréquentielle caractéristique : actionnement éléctromagnétique (0-600 Hz), auto-oscillation assistée (400-1500Hz) et auto-oscillation (1kHz – 2.5 KHz). Les prototypes fabriqués montrent quant à eux une vitesse de sortie supérieure à 100 m/s dans chacune de ces plages fréquentielles. L'optimisation de la géométrie des microvalves a ensuite été réalisée, ainsi qu'un premier packaging permettant la mise en place de barrettes d'actionneurs en soufflerie. Enfin, un microsystème innovant dont l'actionnement est fondé sur la vibration d'une micro-poutre recouverte d'un film magnétostrictif multicouche nanostructuré a été mis au point. Utilisant l'induction d'une instabilité magnétique de type Transition de Réorientation de Spin pour augmenter la sensibilité du système magnétique, nous avons montré qu'un couple de microbobines suffit à l'actionnement de ce type de structure mécanique, mettant ainsi en lumière de nouvelles méthodes d'actionnement tirant avantage des propriétés fortement non-linéaires des films magnétostrictifs au voisinage de la TRS.
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