Wind Impact on Single Vortices and Counterrotating Vortex Pairs in Ground Proximity

Abstract

Wall-resolved large eddy simulations are employed to investigate the behaviour of wake vortices and single vortices in ground proximity at a variety of wind conditions. The six considered strengths of wind, ranging between 0.5 and 4 times the initial wake vortex descent speed, w 0 , include practically and theoretically significant wind speeds. A crosswind of 0.5 w 0 may lead to windward stall posing a potential hazard to subsequently landing aircraft, whereas theoretical considerations predict that at 4 w 0 the rebound of the luff vortex is completely suppressed. The same range of wind speeds is also used to investigate the effects of headwind and diagonal wind in order to discriminate between effects of environmental turbulence increasing with wind speed and the direction of the wind shear. The study has been complemented by a number of single vortex computations in order to differentiate between effects related to the mutual interaction of the vortex pair and the individual vortices with the turbulent boundary layer flow. It is shown that vortex ascent, descent, rebound and decay characteristics are controlled by (i) the interaction of the vortices with secondary vorticity detaching from the ground, (ii) the redistribution of vorticity of the boundary layer which is altering the path of the primary vortices by mutual velocity induction, and (iii) the interaction of the vortices with the environmental turbulence.

Simulation Study of Severity and Mitigation of Wake-Vortex Encounters in Ground Proximity

“…The significant reduction of the maximum jRCRj is in accordance with the results of the WakeOP flight campaign [24] mentioned in Sec. II.B, where lidar measurements showed a reduction of the vortex circulation due to the plate line.…”

“…Lidar measurements confirm the functionality of the plate line [24]. The benefits of the plate line are obvious if the most safetyrelevant, long-lived, and strongest vortices are considered, whose lifetime can be reduced by one third.…”

“…Numerical simulations [24] and lidar measurements conducted at Frankfurt Airport [14] indicate that a crosswind of about half the initial vortex descent speed roughly compensates the vortex-induced propagation speed of wake vortices generated at a height of about one initial vortex separation. The initial vortex descent speed is the self-induced initial sink rate of the vortices in free air (out of ground effect).…”

“…First, the crosswind shear vorticity supports the formation of the secondary vorticity at the lee (downwind) vortex, due to the same sign as the crosswind shear, and attenuates it at the luff (upwind) vortex, due to the opposite sign of the crosswind shear. Second, the primary vortices redistribute vorticity of the crosswind shear, with which they mutually induce transport velocities [24]. These effects lead to an earlier and higher rebound and a more rapid decay of the lee vortex.…”

Multimodel Ensemble Methods for Prediction of Wake-Vortex Transport and Decay

“…In addition, the vortices undergo complex interactions with the ground. Substantial effort has been made in the past to understand the governing physics of vortex dynamics [2][3][4][5][6][7][8] and to develop wakevortex prediction models [9][10][11][12][13][14][15][16][17] to enhance the capacity of the airspace while maintaining the safety.…”