Estimates of the Initial Vortex Separation Distance, b_0, of Commercial Aircraft from Pulsed Lidar Data

摘要

An aircraft in flight generates multiple wake vortices, the largest of which are a result of the lift on the wings. These vortices rapidly roll up into a counter-rotating Vortex pair behind the aircraft. The initial separation between the centroids of vorticity behind the aircraft, or the cores of the resulting Vortex pair, is commonly denoted as b_0. This separation distance is used to estimate the initial Vortex strength (circulation) and to nondimensionalize both time and circulation behind the aircraft. Thus, b_0 is an important parameter in nondimensionalizing aircraft wake measurements. For an elliptically loaded wing, b_0 = (π/4)s, where s is the wingspan of the generating aircraft. The initial descent velocity of the Vortex system behind the aircraft, V_0, is proportional to b_0~(-2). Thus, from estimates of V_0 from lidar measurements, we can estimate b_0. Estimates of V_0 from lidar measurements of Vortex altitude vs. time are presented in the Out of Ground Effect (OGE) region for aircraft arriving at Denver International Airport and San Francisco International Airport. Estimates of b_0 for these aircraft are then obtained. These measurements suggest that, while some estimates of b_0 from commercial aircraft are close to the value based on elliptical wing loading, some aircraft have distinctly nonelliptical values of b_0.