Vincent Chapin

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.

Global Self-Excited Oscillations in a Two-Dimensional Heated Jet: A Numerical Simulation

The aim of this work (Sers 1995) was to develop a numerical methodology to gain insight in the low-density jet spatially developing dynamic with a nonlinear approach. Numerical simulations are shown to differentiate convective and absolute instability regimes and to capture a self-excited global mode in an open flow: the 2D hot jet.

Influence of the air inlet configuration on the performances of a paraglider open airfoil

A finite volume flow solver was used to solve the Reynolds averaged Navier-Stokes equations for the 2D flow field on a paraglider open airfoil. The canopy was assumed to be smooth, rigid and impermeable. The parametric study performed concerns the position and the width of the air inlet at the leading edge. The range of values used covers the air inlet geometries from classical ram-air parafoil to sport paraglider airfoil, including transition toward the full closed baseline airfoil. Results are focused both on lift and drag coefficients for performance analysis and on the internal pressure coefficient which can be critical for a real flexible wing regarding the risk of collapse. Depending on the appearance of a separation bubble over the upper edge, two well separated behaviours can be observed. The first behaviour is more typical of ram-air parachutes and the second one corresponds to the design of performance paragliders. For paraglider configurations, it is shown that the aerodynamic coefficients of the open airfoil can be easily deduced from the pressure coefficients of the baseline airfoil without solving the internal flow.

Improvement of the Jet-Vectoring through the Suppression of a Global Instability

The behaviour of the near-field region of a vertical rectangular jet of aspect ratio 4:1 controlled by a rotating cylinder placed on the jet major-axis is investigated experimentally using a new design facility. The objective is to investigate flow control strategies of a rectangular jet based on instability manipulation. It is found experimentally that the controlled jet exhibits a similar behaviour to the one described theoretically and numerically by Hammond and Redekopp [1, 2] on bluff-body wakes with higher control efficiency when the global instability mode is suppressed.

Viscous Optimization of Interacting Lifting Surfaces

In this paper, the optimization of interacting lift ing surfaces based on design of experiments (DoE) and response surface technique (RSA) is investigated. Response surfaces of the considered problem are generated through the use of high-fidelity two-dimensional Reynolds Average Navier-Stokes simulations. The large number of simulations necessary to populate response surfaces is obtained by using a n ewly developed automated simulation platform named ADONF  . This platform integrate a RANS, URANS flow solver with an automated CAD and mesh generation algorithm and a panel of optimization tools which may be used to generate approximate response surfaces through design of experiments. To gain knowledge about the potential of these tools t o resolve non linear fluid flow optimization problems, we have used this simulation environment to study a sailing yacht problem. The aerodynamic performance optimization of complex rigs composed by multiple interacting masts and sails has been investigated. This problem is a well known by sailors because of its crucial importance for high speed sa iling yachts and has been a subject of debate and controversy since many years. A new look on this problem is proposed through viscous CFD with parametric and topological optimization. It is a preliminary twodimensional study with a moderate design space size which will be extended to three dimensional problems and a larger design space size.