78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V027: Shaping Up: Delta Wing Flows from Thin to Thick

The flow over triangular wings called delta wings has been studied for at least a century. Such wings have a characteristic pair of vortices that form from the wing leading edge. Similar vortex flows exist over a wide variety of shapes (like boxfish) that look less like delta wings and more like bluff bodies. In this study, we compare the flow over a flat delta wing (which has been well studied), and a boxy delta wing that has a large, smooth bump on its leeward surface. Dye injected at the apex of the wings renders the leading edge vortices visible, and a laser and traverse enable us to reconstruct the dye flow over the wing in three-dimensions. On the boxy wing, the vortices are moved outward relative to the flat wing, and the secondary vortex is no longer visible. On the back of the boxy wing a critical behavior occurs in which the flow is detached at both 10° and 35° angles of attack, but attached at the intermediate angle of 20°. A similar flow phenomenon was first discovered in wind tunnel tests of hatchback cars in the 1970s.