Measurements of leading edge vortices in a supersonic stream

An experimental investigation of the leading edge vortices from a 75° sweptback, sharp edge delta wing has been carried out in a Mach 2.49 stream. Five-hole conical probe traverses were conducted vertically and horizontally through the primary vortices at the trailing edge and at one half chord downstream station for 7° and 12° angles of attack. The main objective was to determine the Mach number and pressure distributions in the primary vortex and to present comparisons of flow properties at different survey stations. In response to the continued interest in efficient supersonic flight vehicles, particularly in the missile arena, the motivation for this research has been to provide the quantitative details of supersonic leading edge vortices, the understanding of which up to now has been largely based on flow visualizations and presumed similarity to low speed flows.; As a prerequisite to the measurement campaign, the employed five-hole conical probe was numerically calibrated using a three-dimensional Thin Layer Navier-Stokes solver in order to circumvent the traditional experimental approach vastly demanding on resources. The pressure readings at the probe orifices were computed for a range of Mach numbers and pitch angles, and subsequently verified in wind tunnel tests. The calibration phase also demonstrated the profound influence of the probe bluntness on the nearby static pressure ports, its relevance to the ultimate modeling strategy and the resulting calibration charts. Flow diagnostics of the leading edge vortices included both qualitative flow visualizations, as well as quantitative measurements. Shadowgraphs provided information regarding the trajectory and relative size of the generated vortices while assuring that no probe-induced vortex breakdown occurred. Surface oil patterns revealed the general spanwise locations of leeward vortices, and confirmed topological similarity to their low speed counterparts.; The probe measurements revealed substantial Pitot, total and static pressure deficits in the vortex core. The magnitude of these deficits increase with increasing angle of attack for the same measurement plane and decrease with downstream distance from the model. Pressure deficits in the same survey station also grow spatially with the higher incidence angle. Very large swirl Mach numbers, at times reaching low supersonic values, were recorded and their distribution resembles that of the classical low speed Lamb-Oseen vortex. At the core edges, the presence of substantial radial flow directed towards the vortex center indicates the entrainment of the surrounding fluid. A decrease in the radial Mach number component confirms the change in vortex trajectory from a strong downward flow over the planform to a gradual return towards the free stream in the near-wake. The axial profiles follow the general trend exhibited in the total Mach number distribution thereby confirming the dominance of the streamwise flow. The axial Mach number profiles also demonstrated that the initially conical convection over the wing does not proceed in the wake as a uniform translation of the profiles found at the trailing edge. Most remarkably, contrary to its transonic and low speed counterparts, the axial Mach number profiles exhibit a strong wake-like behavior. Consistent with the shadowgraphs and other existing flow visualizations, measurements illustrated vortex shape adjustment in the near-wake. In the absence of the constraint from the wing surface, the primary vortices stretch in the vertical direction while convecting downstream where a more round shape is ultimately developed.