The Motion of Aircraft Trailing Vortices

Abstract

We use our new knowledge of the motion of turbulent vortex rings [1] to speculate upon the dynamical characteristics of the trailing vortex pair which forms the wake of a lifting surface. We present an interpretation of common observations which suggests that the gross features of the two systems are similar, at least before the aircraft wake distorts due, among other things, to a self-induced instability. The theory presented in [1] is extended to the two-dimensional case and predictions of the shape of aircraft trails are displayed in nondimensional form. As a special case we present a preliminary prediction for the wake shape of a 747, in cruise condition, for a set of parameters that are only approximately correct. Only comparison with actual observations can further refine these guesses. Unfortunately the required observations are not available for any aircraft type. However, the present work suggests a program of measurements which would help in narrowing the possible parameter range. Comments on the motion of vortex rings and vortex pairs in a stratified atmosphere complete the presentation.