Measurements of wake vortices interacting with the ground

Abstract

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.

Wake Vortex Effects on Parallel Runway Operations

“…Although not shown here, the A-300, A-310, A-319, and A-320 showed the same results. (A review of previous data collection efforts 3,7,19 showed a similar result.) NonDimensional Units Vortex Survival Probability…”

“…This works well for vortices at altitude and has been used with some success for vortices near the ground. 7,19 However, because of the presence of the ground, the inertial subrange concept might be inadequate.…”

“…19 Recall that Figure 17 shows that half of the vortices have decayed after about 5 times the non-dimensional lifetime. Figures 9 and 11 show that the vortex survival probability has both an exp(-αD 2 ) distance dependence and an exp(-βt 2 ) time dependence.…”

Suppression of vorticity in vortex and pipe flow interactions

“…However, most of the previous work has been based on vortex flow in the free-stream and the interaction of vortices and boundary layers has been less discussed. The development of vortices in the wake of an aircraft at take-off and landing involves the interactions with the ground surface and has important safety applications [8]. The vortices are forced into the ground surface owing to the downwash effect, subsequently inducing boundary layer separation and the generation of secondary vortices with opposite vorticity [11].…”

Ultrasonic Method for Aircraft Wake Vortex Detection

“…Behavior of wake vortices is widely shown to be altered by proximity to the ground [5][6][7], as well as by various atmospheric conditions [8,9]. A numerical simulation by Corjon and Poinsot [5] finds that ground proximity and resulting viscous flow produce a secondary pair of vortices that induce the original wake vortices to move upward; experimental studies confirm formation of secondary vortices as a result of proximity to the ground [6].…”