Prediction de l'Eclatement Tourbillonnaire sur les Ailes Delta d'Avions Militaires (CFD Prediction of Vortex Breakdown on Delta Wings for Military Aircraft)

摘要

If we want to control vortex breakdown on a delta wing of a military aircraft in order to create rolling moments or improve stability at high angle of attack. the use of CFD simulations may help us to improve our understanding of the flow mechanisms that occur with the use of specific control devices. The first step of such studies is to make sure that we can simulate properly and with accuracy vortex breakdown on a delta wing without any control device. At Dassault Aviation we have done some computations (both Euler and Navier-Stokes) on Mirage 2000 delta wing in a high angle of attack configuration (with deflection of the 2 slats). On such a complex industrial configuration the flow over the wing is a mixing of the vortices coming from the apex, the inner slat and the outer slat. Euler computations lead to unsteady convergence, but the average forces allowed a correct prediction of the occurrence of the maximum of lift coefficient versus incidence. Navier-Stokes computations for the maximum lift coefficient showed that the wing vortices were fully burst, though it was not the case on the experimental pressure distributions. Several ways of improvement are considered. The first one is to greatly improve the mesh discretization in the region of the vortex. A second one is to improve the turbulence model: one knows very well that classical kappa-epsilon models are unable to simulate properly turbulence in rotation, which is the case in the shear layers that build the vortex core.