Numerical prediction of the interference drag of a streamlined strut intersecting a surface in transonic flow

Abstract

This paper presents the numerical evaluation of the interference drag produced by a streamlined strut intersecting a flat wall in transonic flow. The calculations were performed on unstructured grids using the FUN2D and FUNBD codes and the SpalartAllmaras turbulence model. The grids were generated with AFLR2 and VCRIDns. The impact of the thickness to chord ratio of the strut, the Reynolds number, and the effect of the angle made by the strut with the wall are studied for both inviscid and viscous flows. The interference drag is calculated as the drag increment of the arrangement compared to an equivalent two-dimensional strut of the same crosssection. The interference drag coefficient is based on a conveniently chosen reference area. The results show a rapid increase of the interference drag as the angle of the strut deviates from a position perpendicular to the wall. Separation regions appear for low intersection angles, but the viscosity generally provides a positive effect in alleviating the strength of the shock near the junction and thus the drag penalty. When the thickness-to-chord ratio of the strut is reduced, the flowfield is disturbed only locally at the intersection of the strut with the wall. This study provides an equation to estimate the int,erference drag of simple intersections in transonic flow. To better understand the Abw in the region where the strut and the wall intersect, the flowfield is analyzed in a detailed fashion for the thickest strut with contours plots and streamtraces.