Compact differences scheme applied to simulation of low-sweep delta wing flow

Computational simulations are presented of the flow over a 50-deg sweep delta wing for angles of attack a 5, 10, and 15 deg. The full Navier-Stokes equations are solved using a sixth-order compact differencing scheme coupled with an eighth-order low-pass spatial filter to provide numerical stability. For the 5-deg angle-of-attack case, a dual primary vortex system develops. over the wing. At the higher angles of attack, this dual vortex. structure diminishes and is replaced by a more classic primary, secondary, tertiary vortex structure. For alpha = 10 and 15 deg, the flow becomes increasingly unsteady with vortex breakdown occurring over the wing. For this low-sweep angle, the vortex core does not exhibit the distinct spiral winding normally present in vortex breakdown for higher sweep angles. A transition from jetlike to wakelike flow does occur in the vortex core with the corresponding switch in sign of azimuthal vorticity. No actual flow reversal is observed in the mean flow, despite isolated pockets of reversed axial flow being present in the instantaneous flow. The onset of breakdown is le ss abrupt than that observed over slender delta wings, with the breakdown region having. a more conical shape. These breakdown features make it more difficult to, define a specific location for the vortex breakdown point. Upstream of breakdown, a periodic wandering of the vortex core is observed, which results from the formation and shedding of vortical structures in the shear layer emanating from the leading edge of the delta wing and from the eruptive response of the secondary flow.