Experimental Investigations on Fluidic Control Over an Airfoil

International audienceThis study presents the development of two fluidic actuators − namely, microjets and tangential blowing actuator (TBA), designed for flow separation control. The developed actuators are compact enough to fit inside an ONERA D profiled wing with a chord of 0.35 m. Test bench experiments showed that the microjets (resp. TBA) were able to produce exit velocities up to 330 m/s (resp. 60 m/s). These actuators were placed in the model and were tested in wind tunnels for various blowing rates. The investigations included the use of force balance measurements, on-surface flow visualization with pigmented oil, off-surface flow visualizations with smoke, surface pressure distribution measurements, and Particle Image Velocimetry (PIV). Most of the tests were performed at free-stream velocities between 20 m/s (for PIV) and 40 m/s, corresponding to Reynolds numbers in the range 0.47 × 10^6−0.93 × 10^6 . The angle of attack varied from −2 to 20 degrees. Experiments were conducted using the naturally occurring laminar boundary layer as well as for a turbulent boundary layer. In such a case, rough strips were used in the vicinity of the leading edge. The present tests show the efficiency of these devices to delay separation and improve aerodynamic performances of the wing: for example, a maximum of 30% gain in CL has been reached using the microjets. Both actuators tend to increase the lift coefficient CL after stall and areas of separated flow have been eliminated by applying control, as suggested by flow visualizations and PIV velocity fields

The periodic pulse photothermal radiometry technique within the front face configuration

The front face photothermal radiometry technique has been improved in order to estimate the thermal conductivity of thin films with better accuracy compared to existing techniques. The experimental pro- cedure is based on the front face response to a nanoseconds laser pulse repeated periodically at high fre- quency, i. e., a Dirac comb waveform. Averaging the thermal response by considering thousands successive pulses allows improving largely the signal noise ratio. The unknown thermal properties and related experimental parameters are identified by minimizing the gap between the measured signal and the theoretical response that accounts with the pulse waveform, the repetition frequency and the detector transfer function. Minimization is first achieved by implementing first a simplex technique that gives an initial set of values to start the Metropolis–Hastings algorithm in a second step. Application of the proposed methodology is done considering amorphous GeTe film deposited on a Si wafer. It is shown that this experimental method as well as the implementation of the Bayes minimization technique allows to identify the thin film intrinsic thermal conductivity with high accuracy considering some uncertainty on the other parameters assumed to be known

Signal noise ratio improvement technique for bulk thermal diffusivity measurement

International audienc

Au-delà du conflit et de la négociation ?

National audienceDepuis la création de Sociologie du travail, les conflits et les négociations ont changé d'importance et de forme. Ils ne portent pas non plus nécessairement sur les mêmes enjeux. En raison de l'apparition de nouveaux acteurs sur les scènes de la contestation et de l'émergence de nouvelles stratégies de lutte sociale, les notions de "conflit" et de "négociation" méritent d'être revisitées au regard des formes de circulation en différents univers (État, syndicat, patronat, associations). Même si elle fait débat, la place du droit dans les relations de travail d'aujourd'hui suscite à ce sujet un intérêt tout particulier