Active control of a stalled airfoil through steady or unsteady actuation jets

The active control of the leading-edge (LE) separation on the suction surface of a stalled airfoil (NACA 0012) at a Reynolds number of 106 based on the chord length is investigated through a computational study. The actuator is a steady or unsteady jet located on the suction surface of the airfoil. Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations are solved on hybrid meshes with the Spalart–Allmaras turbulence model. Simulations are used to characterize the effects of the steady and unsteady actuation on the separated flows for a large range of angle of attack (0<a<28 deg). Parametric studies are carried out in the actuator design-space to investigate the control effectiveness and robustness. An optimal actuator position, angle, and frequency for the stalled angle of attack a¼19 deg are found. A significant increase of the lift coefficient is obtained (+84% with respect to the uncontrolled reference flow), and the stall is delayed from angle of attack of 18 deg to more than 25 deg. The physical nonlinear coupling between the actuator position, velocity angle, and frequency is investigated. The critical influence of the actuator location relative to the separation location is emphasized

Cours : Rendu Expressif

National audienceIntroductory course on Expressive Rendering.Cours d'introduction au rendu expressif

Relevance Of Reduced Tillage Practices On Soil Biological, Chemical And Physical Quality And Ecosystem Services Under Organic Farming Context In Britany

Avoiding or limiting ploughing under organic farming management remains a big challenge for organic farmers. By developing an holistic approach, the aim of this study was to evaluate the impact, under organic farming management, of different tillage techniques on soil biological, physical and chemical quality and ecosystem services. In an experimental site located in Britany (France) four tillage techniques were compared: conventional ploughing (CP), agronomic ploughing (AP), superficial non-inversed tillage (C15) and very superficial non-inversed tillage (C8). Results, obtained during 10 years (from 2003 to 2013), showed a strong temporal variability between years, however some results appeared consistent. Positive impact of reduced tillage on hydraulic conductivity and organic matter content was limited to the 0-5 cm depth. No-inversed tillage (C15, C8) and agronomical ploughing (AP) significantly improved microbial biomass. C8 is the only technique which significantly decreased nematofauna. Earthworm biomass significantly decreased under conventional ploughing (CP) due to the decrease of anecic species while ploughing techniques (CP, LA) preserved total earthworm abundance due to endogeic species. Endogeic species had a negative impact on hydraulic conductivity whereas anecic enhanced the conductivity and Carbon and Phosphorus contents. No-inversed tillage techniques (C8, C15) leaded to a decrease of the crop yield, due to an increase of weeds which increased water and nutritive competition. This study highlighted the interests and limits of no-inversed techniques and agronomical ploughing applied in organic farming management for enhancing soil quality and crop yield

Pourquoi les stars du sport sont-elles aussi bien payées ?

La rémunération des meileurs joueurs de football peut paraître excessive, elle obéit pourtant à un calcul économique classique, celui du marginalisme. Dans cette logique, l'introduction d'une limitation au niveau des salaires serait une mesure risqué

Le château de Neuville-sur-Ailette (Aisne) : état des recherches

International audienceLe site du château de Neuville a fait l’objet de deux diagnostics complétés par des recherches documentaires et des observations de surface en dehors de l’emprise des deux opérations archéologiques.Les vestiges imposants d’un bâtiment médiéval ont été dégagés. Cette construction aux caractéristiques monumentales appartient au château de Neuville. Réoccupé pendant la Première Guerre mondiale par l’armée allemande, ce bâtiment a fait l’objet d’un réaménagement intérieur et un dessin y a été peint. Pilonné pendant ce conflit, il a ensuite en grande partie été remblayé.Une restitution du tracé de l’enceinte castrale a été proposée. La confrontation des différents résultats nous a également amené à réfléchir à l’implantation du château construit au lendemain des guerres de Religion en remplacement de l’ancienne forteresse médiévale.L’emprise du cimetière qui s’étendait dans l’espace situé entre l’église et le château a enfin été partiellement circonscrite. L’une des tombes fouillées indique une occupation relativement précoce de cet espace funéraire dans les années 1170-1268