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

Abstract

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 hazardous because the updraft velocities of a thermal may compensate the induced descent speed of the vortex pair such that the vortices stall in the flight path. The LES results illustrated that 1) the primary rectilinear vortices are rapidly deformed on the scale of alternating updraft and downdraft regions; 2) parts of the vortices stay on flight level but are quickly eroded by the turbulence of the updraft; 3) the longest living sections of the vortices are found in regions of relatively calm downward flow, which augments their descent. Strip theory calculations are used to illustrate the temporal and spatial development of lift and rolling moments experienced by a following medium weight class B-737 aircraft. Characteristics of the respective distributions are analyzed. Initially, the maximum rolling moments slightly exceed the available roll control of the B-737. After 60s the probability of rolling moments exceeding 50% of the roll control has decreased to 0.009% in a safety corridor around the glide path.