A study of jets in crossflow and its application on wingtip blowing

The objective herein is to study the flowfield associated with jets in crossflow and their applications to the flowfield near the tip of a wing. The study was both numerical and experimental. The flowfields of different shaped jets orientated in crossflow were studied numerically. The predicted flow features generally agreed well with measurements and observations. Qualitatively, most of the basic flow physics were captured numerically, particularly for circular jet cases where data is available for comparisons. Periodic vortex formations were captured both at the front and the rear bound shear layers of the jet plume. The well known counter-rotating vortex pair is symmetric for a symmetrically oriented jet but is asymmetric for asymmetric jet. The source of these vortices is the jet-pipe boundary-layer vorticity. For any shaped jet, a pair of vertical twin tornado-like wake vortices would always form behind the jet plume due to the lower pressure at that region. These wake vortices are asymmetric in position and different on size for an asymmetrically placed jet. The source of these vortices is the crossflow boundary-layer vorticity. An experimental investigation of discrete wingtip jets was also conducted in both water and wind tunnels as an important application. Careful flow visualization revealed that the local perturbation introduced by the wingtip jet closely resembles that of asymmetric jets blowing from a flat plate. All types of vortices observed in the latter flowfield were identified in the flow field generated by the wingtip jet. It was reconfirmed that the wingtip jets effectively dispersed the tip vortex and the individual jet location and blowing momentum are the major parameters. Wing surface pressure measurements indicated that wingtip jets affected the global surface pressure distribution over the wing and improved its lift.