Compressibility effects on vortex breakdown onset above a 75-degree sweep delta wing

Abstract

The effects of compressibility on the onset of vortex breakdown above a 75-deg sweep delta wing were explored numerically for both static and pitching conditions. The flows were simulated by solving the mass-averaged, three-dimensional, unsteady Navier-Stokes equations using an implicit, time-accurate Beam-Warming algorithm and the algebraic Bald win-Lomax turbulence model. Static computations were performed over the freestream Mach number range 0.2 < M^ < 0.95 and for a chord Reynolds number Rec = 2 x 10 6. Compressibility was found to have a pronounced effect on the flow structure for static conditions. The formation of several shocks and an embedded supersonic region in the vortex core (for M^ as low as 0.4) were encountered prior to the onset of vortex breakdown. Despite these drastic changes in the flow structure, the quasistatic breakdown onset angle varied only slightly. Compressibility effects on the transient onset of vortex breakdown were also investigated for a ramp-type pitch maneuver to high angle of attack with 0.2 < Mx ^ 0.6. Under dynamic conditions increasing Mv, resulted in a larger delay of breakdown and in the formation of a complex, three-dimensional shock structure at Mx = 0.6. Compressibility effects were found to be similar when comparing the results from laminar and turbulent pitching calculations, indicating that these effects are to a great extent in viscid in nature.