Near-field wingtip vortex characteristics of a rectangular wing in ground effect

The aerodynamics and near-field wingtip vortex characteristics of a rectangular wing with NACA4412 section in ground effect (GE) are studied in this paper. The steady compressible Reynolds-Averaged Navier-Stokes (RANS) equations with the Spalart-Allmaras (SA) turbulence model are discretized using the finite volume method. Based on the pressure and lift variations in GE, a 3D rectangular wing can be divided into two parts along the span-wise direction: the quasi-2D inner part of the wing (away from wing tip) in which the lift increases monotonously, and the second part near the wingtip in which the lift decreases. In GE, the wingtip vortex moves outward along the span-wise direction due to the ground mirror effect, and rebounds in the vertical direction due to the induction from the secondary vortex generated from the ground boundary layer. In GE, the strength of the near-field wingtip vortex along the flow direction depends not only on the initial vortex strength and the shear layer developing from the trailing edge of the wing, but also due to the generation of secondary vortex in the ground boundary layer, and the interaction between the wingtip vortex and the secondary vortex.