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 hazardousbecausetheupdraft velocitiesofa thermalmay compensatetheinduceddescent speed ofthevortex pair such that the vortices stall in the e ight path. The LES results illustrate 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 e ight level but are quickly eroded by the turbulence of the updraft; 3 )the longest living sections of the vortices are foundinregionsofrelativelycalmdownwarde ow,which augmentstheirdescent.Striptheory calculationsareused 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 theavailableroll controloftheB-737. After60 sthe probability ofrolling moments exceeding 50% of the roll control has decreased to 0.009% in a safety corridor around the glide path. Nomenclature b = aircraft span b0 = initial vortex spacing c = section chord cl = section lift coefe cient dP = probability difference g = gravitational acceleration k = wave number