Wake vortices in convective boundary layer and their influence on following aircraft

The decay of three wake vortex pairs of a B-747 aircraft in an evolving and convectively driven atmospheric boundary layer is investigated by means of large-eddy simulations (LES). Convective boundary layers are considered ha zardous because the updraft velocities of a thermal may compensate the indu ced descent speed of the vortex pair such that the vortices stall in the fl ight path. The LES results illustrate that 1) the primary rectilinear vorti ces are rapidly deformed on the scale of alternating updraft and downdraft regions; 2) parts of the vortices stay on flight level but are quickly erod ed by the turbulence of the updraft; 3) the longest living sections of the vortices are found in regions of relatively calm downward how which augment s their descent. Strip theory calculations are used to illustrate the tempo ral and spatial development of lift and rolling moments experienced by a fo llowing medium weight class B-737 aircraft. Characteristics of the respecti ve distributions are analyzed. Initially, the maximum rolling moments sligh tly exceed the available roll control of the B-737. After 60 s the probabil ity of rolling moments exceeding 50% of the roll control has decreased to 0 .009% in a safety corridor around the glide path.