Effects of an upstream triangular plate on the wing-body junction flow

Abstract

The use of a short triangular leading-edge plate at the base of a wing-body junction is experimentally evaluated as a passive control method to eliminate the horseshoe vortices or at least to subdue their strength. The impact of the plate geometry on the efficacy of the control is assessed by considering triangular plates that have a length of 1T, 2T, and 3T, a width of 0.1T and 0.2T, and a height of 1.5T, where T is the maximum thickness of the wing. The wing model is a NACA 0020 airfoil. The Reynolds number based on the chord length is varied from Rec = 25 000 to 75 000. The incoming boundary layer is laminar in all experiments. Particle Image Velocimetry is utilized to characterize the temporal behavior and circulation strength of horseshoe vortices. The λ2-criterion is used as the vortex identification method. All the triangular leading-edge plates investigated in this study are found to decrease the circulation strength of the horseshoe vortices in the symmetry plane, although by varying degrees, compared to the baseline configuration that has no plate control. An increase in the upstream reach of the leading-edge plate significantly mitigates the vortical organization, vorticity, size, and circulation strength of horseshoe vortices. Although all plate lengths in question achieve a regression in the horseshoe vortex regime and, at the lowest Reynolds number considered, they all reduce the number of horseshoe vortices compared to the uncontrolled case, as the Reynolds number increases, longer plates are needed for such an effect. On the other hand, an increase in the thickness of the leading-edge plate deteriorates the desired control by increasing the vortical organization, vorticity magnitude, size, and circulation strength of horseshoe vortices. At higher Reynolds numbers, a thicker plate performs even poorer, resulting in extra horseshoe vortices, which can be unsteady depending on the Reynolds number. Nevertheless, all the triangular plates considered in this investigation, including the thickest one, outperform the baseline case. Overall, the proposed method is found to be an effective way for the mitigation of horseshoe vortices at the wing-body junction. The longer and thinner the plate, the better the vortex mitigation.