Measurements of Wake Vortices Interacting with the Ground

Although wake vortices are known to decay more rapidly near the ground than away from the ground, the details of the ground interaction are not well understood. Propeller anemometer arrays located under the approach path have been used to study vortex transport and provide some information about the vortex interaction with the ground, such as the generation of secondary vortices via boundary-layer detachment. A propeller anemometer array at John F. Kennedy International Airport using 8.5-m poles was augmented with 1) a sonic anemometer measuring three-dimensional wind and temperature at 10 Hz and 2) a vertical array of vertical wind and crosswind anemometers, mounted at four additional levels (4.2, 3.2, 1.05, and 0.5 m). The sonic anemometer gave 1) measurements of turbulence inside the vortex flowfield and 2) indications of vertical variations in the ambient headwind and temperature, which were brought down to the measurement level by the descent of the vortex recirculation oval. In general, under conditions of low to moderate turbulence, the turbulence level inside the wake vortex flowfield is greater than that in the ambient wind. The vertical anemometer array showed that the crosswind profile under a wake vortex in ground effect has a very thin boundary layer, much thinner than that of the ambient wind. It also provided some details concerning the wind profile of the secondary vortex.