Identification of concentrated structures in slightly compressible flows

National audienceIn this paper, different vortex diagnostic methods are compared to obtain a better understanding of boundary layer influence on the transport of vortical structures involving a complete analysis of vorticity, the Vorticity Threshold Criterion (VTC), and the Weiss Criterion (WC). These three techniques are basically confronted to find a suitable understanding of all flow characteristics for a range of laminar to transitional Reynolds numbers. The computations on this dihedral plane are done using a 2D DNS method. The Weiss criterion, coming from the analysis of the incompressible Euler equations is validated and applied to low speed compressible flows (Mach number=0.2)

Active control of transitional channel flows with pulsed and synthetic jets using vortex methods

International audienceIn this work a vortex method is used to simulate and control an incompressible two-dimensional transitional flow over a backward-facing step. Two different control strategies are implemented to modify the shedding, the recirculation zone behind the step and the transport in the channel. The first technique consists in using a pulsing inlet velocity and the second one is based on local oscillating jets implemented on the step vertical wall. The influence of these controls on the flow behavior is carefuly investigated. Both, open-loop and closed-loop active control approaches are performed

Vortex penalization method for solid-porous-fluid media with application to passive flow control

International audienceIn this work, a coupling of vortex methods with penalization methods is proposed in order to accurately and easily handle solid-fluid-porous media. This immersed boundary approach in- deed maintains the efficiency and the robustness of vortex meth- ods and allows to model the three different media without pre- scribing any boundary condition. In this paper, we propose an application of this immersed boundary method to passive flow control around a semi-circular cylinder, realized adding a porous sheath on the obstacle surface in order to smooth the flow dynam- ics

Passive flow control around a semi-circular cylinder using porous coatings

International audienceIn this paper, the passive control of flow past a semi-circular cylinder is investigated. This control is achieved by adding a porous medium between the solid obstacle and the incompressible fluid in order to reduce drag forces and regularize the flow. A vortex-penalization method is chosen to easily model the flow in the different media. Several configurations of the porous layer are investigated and parametric studies are performed in order to determine the most efficient passive flow control devices. This control study can be considered as a first step to propose efficient strategies to regularize the flow around a side-view mirror

Double-diffusive sedimentation at high Schmidt numbers: Semi-Lagrangian simulations

International audienceWhen particle-laden freshwater is placed above clear saltwater, double-diffusive sedimentation can arise. Navier-Stokes direct numerical simulations by Burns and Meiburg showed that this process can be dominated by either Rayleigh-Taylor or double-diffusive fingering instabilities. Based on two-dimensional simulations, those authors identify a single dimensionless parameter that can be employed to distinguish between these regimes. Here we develop a high-performance semi-Lagrangian computational approach that enables us to extend these high Schmidt number simulations to three dimensions, and to confirm the validity of their proposed scaling law for three-dimensional flows

Modèles numériques pour le contrôle actif et/ou passif d'écoulements tourbillonnaires.

National audienc

Numerical simulation of active and passive control strategies for vortex flows.

International audienc