Observations of Atmospheric Effects on Vortex Wake Behavior

Smoke-marked trailing vortices were generated by a light aircraft under a hierarchy of measured atmospheric stability and turbulence levels, and their motion and decay were recorded photographically. Decay from both sinuous vortex interaction and core bursting type instabilities occurred, with bursting being the dominant mode. Turbulence had a strong effect on wake life, with time-to-breakup for both modes varying as epsilon to the one-third power where epsilon is the turbulent dissipation rate. Observed lifetimes ranged from 6 sec in light-to-moderate turbulence to more than 80 sec in calm, stable air. One exceptionally long-lived solitary vortex was observed for more than 3 min. Atmospheric stratification had a weak influence on wake life, and its effect on wake descent could not be determined, since descent was often stopped by a rolling of the plane of the vortices. The observed data correlate well with a new theory for time-to-breakup.