Closed-loop separation control over a sharp edge ramp using Genetic Programming

We experimentally perform open and closed-loop control of a separating turbulent boundary layer downstream from a sharp edge ramp. The turbulent boundary layer just above the separation point has a Reynolds number $Re_{\theta}\approx 3\,500$ based on momentum thickness. The goal of the control is to mitigate separation and early re-attachment. The forcing employs a spanwise array of active vortex generators. The flow state is monitored with skin-friction sensors downstream of the actuators. The feedback control law is obtained using model-free genetic programming control (GPC) (Gautier et al. 2015). The resulting flow is assessed using the momentum coefficient, pressure distribution and skin friction over the ramp and stereo PIV. The PIV yields vector field statistics, e.g. shear layer growth, the backflow area and vortex region. GPC is benchmarked against the best periodic forcing. While open-loop control achieves separation reduction by locking-on the shedding mode, GPC gives rise to similar benefits by accelerating the shear layer growth. Moreover, GPC uses less actuation energy.Comment: 24 pages, 24 figures, submitted to Experiments in Fluid

CC9 Livestock-Associated Staphylococcus aureus Emerges in Bloodstream Infections in French Patients Unconnected With Animal Farming

We report 4 bloodstream infections associated with CC9 agr type II Staphylococcus aureus in individuals without animal exposure. We demonstrate, by microarray analysis, the presence of egc cluster, fnbA, cap operon, lukS, set2, set12, splE, splD, sak, epiD, and can, genomic features associated with a high virulence potential in human

Effects of Super-Hydrophobic Coatings on Free Falling Spheres

International audienceThe present work deals with a joint experimental investigationof free falling super-hydrophobic spheres in pure water at rest.The results derive from a collaboration between the Universityof Orl ́eans (France) and the Monash University (Australia). Thesuper-hydrophobic coatings have the ability, once immersedinto water, to reduce the contact area between the liquid andthe solid surface by entrapping an air layer in the surface rough-ness. We thus investigate a possible effect of this feature onthe hydrodynamic drag of spheres, focusing on the terminal ve-locity region. Surprisingly, the hydrodynamic performance ofsuper-hydrophobic coatings depends on the analysed Reynoldsnumber regime. The drag increase evidenced for the small di-ameter spheres tends progressively to turn into a drag attenu-ation for the largest diameters spheres. A possible connectionbetween the hydrodynamic performance and the deformation ofthe air layer encapsulating the coated spheres is proposed

Effects of Super-Hydrophobic Coatings on Free Falling Spheres

International audienceThe present work deals with a joint experimental investigationof free falling super-hydrophobic spheres in pure water at rest.The results derive from a collaboration between the Universityof Orl ́eans (France) and the Monash University (Australia). Thesuper-hydrophobic coatings have the ability, once immersedinto water, to reduce the contact area between the liquid andthe solid surface by entrapping an air layer in the surface rough-ness. We thus investigate a possible effect of this feature onthe hydrodynamic drag of spheres, focusing on the terminal ve-locity region. Surprisingly, the hydrodynamic performance ofsuper-hydrophobic coatings depends on the analysed Reynoldsnumber regime. The drag increase evidenced for the small di-ameter spheres tends progressively to turn into a drag attenu-ation for the largest diameters spheres. A possible connectionbetween the hydrodynamic performance and the deformation ofthe air layer encapsulating the coated spheres is proposed

Active flow control using pulsed micro-jets on a full-scale production car

This paper presents experimental flow control results obtained on a full-scale production car in a wind tunnel. The aim of this paper is to demonstrate the feasibility of controlling the separated flow over the rear part of the car by using pulsed micro-jets. Pulsed micro-jets are produced by hybrid actuators mixing both standard and MEMS (Micro Electro Mechanical Systems) technology. Both actuation frequency and injected momentum are studied. Experiments show a small influence on the drag force (less than 1% reduction), but a stronger one on the lift force (up to 9% reduction). Wall pressure coefficients measurements highlight the suppression of the recirculation bubble over the rear window, along with a reinforcement of the longitudinal C-pillars vortices. Spectral measurements in the shear layer above the rear window show that most efficient control frequencies match the shear layer instability frequency, and that the actuation suppresses the energetical contribution associated with the recirculation bubble frequency. Additional measurements demonstrate that a minimum threshold value of the momentum coefficient is needed for the flow actuation to be efficient. This is the first experimental evidence of the efficiency of micro perturbations (380$μ$ m thick micro-nozzles) to control flow separation on a full- scale production car. This is a very important step in the perspective of future applications of flow control in automotive industry to improve aerodynamics performances and reduce CO2emissions