Improved Unsteady RANS Models Applied to Jet Transverse to a Pipe Flow

An unsteady RANS model is developed in order to simulate the complex situations involving both free and bounded flows. This model tuned to catch coherent flow structures is developed both in the k-ε and k-l approaches. The full 3D geometry of a round jet exiting from a reservoir into a pipe has been computed. Periodic conditions are applied in order to compare with an experiments consisting of eight jets exiting in a cross pipe flow. Improvement has been obtained with this URANS turbulence model compared to RANS and good agreement compared with experiments has been obtained. Unsteady phenomena are reproduced by the model and provide more insight into the physical properties of the flow and of the transport of a passive scalar

Impact of the Automotive Aerodynamic Control on the Economic Issues

Sustainable development associated with the need to reduce the energy consumption and to offer more creative freedom to the automobile designers requires looking for new solutions of control without appendix added nor geometrical modification. Among these solutions, the active flow control by fluidic actuators constitutes an interesting alternative. Various configurations of control are thus tested in order to reduce the aerodynamic drag. The results show that protocols based on control by suction, blowing or intermittent jet allows reducing the aerodynamic drag and consequently the consumption and CO2 emissions

Mass entrainment-based model for separating flows

Recent studies have shown that entrainment effectively describes the behavior of natural and forced separating flows developing behind bluff bodies, potentially paving the way to new, scalable separation control strategies. In this perspective, we propose a new interpretative framework for separated flows, based on mass entrainment. The cornerstone of the approach is an original model of the mean flow, representing it as a stationary vortex scaling with the mean recirculation length. We test our model on a set of mean separated topologies, obtained by forcing the flow over a descending ramp with a rack of synthetic jets. Our results show that both the circulation of the vortex and its characteristic size scale simply with the intensity of the backflow (the amount of mass going through the recirculation region). This suggests that the vortex model captures the essential functioning of mean mass entrainment, and that it could be used to model and/or predict the mean properties of separated flows. In addition, we use the vortex model to show that the backflow (an integral quantity) can be estimated from a single wall-pressure measurement (a pointwise quantity). This finding encourages further efforts toward industrially deployable control systems based on mass entrainment.French National Research Agency (ANR) through the Investissements d’Avenir program, under the Labex CAPRYSSES Project (ANR-11-LABX-0006-01)

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

Massive separation control analysis of the pulsed jet actuators effects

The aerodynamic drag of simplified car geometry with small span and strongly separated wake can be reduced up 20% by using pulsed jet distributed along the rear window. Results show an enhancement of transversal wake size in the control region, a displacement of the mean positions of vortex wake structures, a decrease of velocities near the rear part and a reduction of vortex structure recirculation in the wake. These modifications produced by the control are analyzed, commented and model based on simple strategy to build efficient and suitable separation control strategy is proposed

Compressible effects on a temporal direct numerical simulation

Direct numerical simulation of a temporal compressible mixing layer has been performed through the mixing layer transition at convective Mach number 0.4 with massively parallel computer. Finite volume method has been used to solve the full time-dependent, compressible Navier-Stokes equations without turbulence models. Numerical simulation initialized by the most amplified linear instability waves is then presented. 1923 mesh size is used to describe full scales. Roll-up and pairing process have developed and have been described, showing the highly two dimensional feature of the mixing layer. The influence of the phase between the two- and three-dimensional initially pertubated waves has been revealed

Instability of canopy flows

International audienceHonami and monami waves are caused by large-scale coherent vortex structures which form in shear layers generated by canopies. In order to reach new insights on the onset of such waves, the instability of these shear layers is studied. Two different approaches are used. In the first approach, the presence of the canopy is modeled via a drag coefficient, taken to vary along the canopy as by experimental indications. The second approach considers the canopy as a porous medium and different governing equations for the fluid flow are deduced. In this second case, the anisotropy of the canopy, composed by rigid cylindrical elements,is accounted for via an apparent permeability tensor. The results obtained with the latter approach approximate better experimental correlations for the synchronous oscillations of the canopy