Le projet e-MECA : electro-Mécanique Embarquée à Compacité Améliorée, dont l’objectif est de concevoir une machine ultra compacte et ultra rapide à une puissance utile de 12Kw, trouve son application dans les véhicules mild et full hybrides. Ce type de machine présente en effet un fort potentiel de déploiement industriel en très grandes séries à des prix abordables. Pour ces machines, les pertes de charge liées aux écoulements dans le jeu constituent des enjeux essentiels pour les constructeurs. La présente étude porte sur le moyen d’identifier de ces pertes des machines électriques ultra-compactes et ultra-rapides (50 000 rpm).Cette thèse a pour objet l’étude des pertes aérauliques dans l’espace entre le rotor et le stator d’une machine électrique ultra-rapide (≈ 250 m/s) et ultra-compacte (0,5mm - 2mm d’entrefer), en cherchant à répondre aux spécifications élaborées par nos partenaires dans le cadre du projet e-MECA. / The project e-MECA: electromechanical engineering Embarked in Improved Compactness, the objective of which is to design a machine with a small gap and high speed rotor with a useful power of 12Kw, finds its application in mild and hybrid vehicle. This type of machine indeed presents a high potential in the industrial deployment in very big series to affordable prices. The losses in these machines are linked to the flow in the gap has a significant importance for the manufacturers. This study aims to identify these losses for the ultra-compact and ultrafast electric machines (50 000 rpm).This thesis is a study of the air losses in the space between the rotor and the stator of an ultra-fast electric machine (≈ 250 m/s) and ultra-compact (0,5mm - 2mm of air-gap). This study was done to meet the specifications that had been elaborated by our partners in the e-MECA project.

The interaction of a liquid drop with a solid surface is being actively studied to understand practically encountered scenarios such as the impact of fuel spray droplets onto the walls of engine combustion chamber, the formation of thermal barrier coating on the surfaces of turbine blades, the process of ink-jet printing, etc. The surface topography of solid surface is one of the major parameters influencing the dynamics of drop-surface interaction process. Understanding the precise role of surface topography features such as micro asperities and grooves on the spreading and receding processes of impacting liquid drops is crucial for the improvement in abovementioned applications. Recent developments in the fabrication of micro- and nano-structures on solid surfaces provide fabulous opportunities to investigate the role of single/multiple micro asperities and grooves on the dynamics of impacting drops. The thesis deals with an experimental work on the impact of water drops on stainless steel surfaces comprising unidirectional parallel grooves. A group of six target grooved surfaces covering a wide range of surface wettability were considered. The target surfaces were prepared using the techniques of photolithography, electro discharge machining, and laser machining. Scanning electron microscope and optical surface profilometer were used to characterize the groove texture geometrical parameters of the target grooved surfaces. The experiments of drop impact were carried out in an experimental apparatus consisting of a liquid drop generator, a substrate table, and a digital video imaging system. Free-falling distilled water drops released from a certain height were allowed to impact normally on the target surfaces. The image sequences of drop impact dynamics were constructed from the images captured using the digital video imaging system. Majority of the drop impact experiments were captured using a high speed video camera operating with frame speed ranging from 3000 to 10000 fps. For the target grooved surfaces, the impact dynamics was analyzed for the impacting drop liquid oriented both in the direction perpendicular to the grooves ( ) and in the direction parallel to the grooves (||) via independent test runs. The captured digital frames were used to deduce the temporal variation of impacting drop parameters such as drop contact diameter, drop contact angle, and drop height at the center of impacting drop with the aid of image processing software. The impacting drops were characterized in terms of Weber number, We expressed in terms of drop impact velocity and drop diameter measured just before the start of impact process. The study covered We ranging from 1.8 to 170. In general, the groove texture on the solid surface influences the drop impact process for all We examined in the study. The effect is more pronounced for the receding of impacting drops. For high We drops, the groove texture enhances the perturbations seen at the periphery of spreading lamella. The study showed quantitatively that the drop impact process on a target grooved surface comprising unidirectional parallel grooves develops a non-axisymmetric drop flow on the grooved surface exhibiting different spreading and receding processes of impacting drop liquid in the directions perpendicular ( ) and parallel (||) to the grooves. The maximum spreading diameter reached immediately after the completion of early inertia-dominated spreading in is less than that obtained in || due to the loss of drop kinetic energy caused by the pinned motion of drop liquid in . The non- axisymmetric drop flow on the target grooved surface develops a difference between the frequencies of contact angle oscillation of impacting drop liquid in  and ||. The frequency difference in contact angle oscillation causes the beating phenomenon in the temporal variation of the contact angle anisotropy, Δθ and drop height at the center of impacting drop, Z. For a given target grooved surface, the experimental measurements suggested that the beat frequency is almost independent of We. The temporal variation of Δθ and Z do not show the traces of beating phenomenon for the impact of high We drops. Owing to the non-axisymmetric drop flow, the final equilibrium drop shape is eccentric for the impact of low We drops and approaches a circular shape for the impact of high We drops. The role of groove texture geometrical parameters is seen in the drop impact process via the surface wettability especially for the impact of low We drops. Larger surface roughness factor makes the target grooved surface to exhibit hydrophobic characteristics.