Review of real-time wake vortex prediction models

A major concern to the traveling public is increasing the capacity of airports while maintaining safe operating conditions. Therefore, understanding the transport and decay of aircraft wake vortices in all kinds of weather conditions is paramount to this objective. The goal of a recent NASA program was to demonstrate that increased terminal area productivity could be achieved by safely decreasing the separation time behind landing aircraft. This required the prediction of wake vortex strengths and positions as a function of aircraft type and weather conditions. Current spacing standards are based on aircraft weight (i.e., small, large, heavy) of the leading and following aircraft, and were chosen to minimize hazardous wake encounters. The current standards do not consider the affects from weather, such as the transport of the wake out of the flight corridor by strong cross winds.

Although wake vortex behavior has been studied many years, serious controversies existed regarding decay and transport, including Reynold's number effects and influence from weather. Measurements and analysis during NASA's Aircraft Vortex Spacing System (AVOSS) project emphasized the importance of weather on vortex transport and decay. It was clear that the intensity of atmospheric turbulence does affect the decay rate of a wake vortex, with the characteristics of this decay having little in common with the decay of low-Reynold's number vortices. A primary contribution during this program was the development of a real-time physics-based wake prediction model called the AVOSS Prediction Algorithm (APA), which is based on Sarpkaya's “out of ground effect” decay model. In a demonstration at DFW airport, the APA model predicted safe aircraft spacings between leading and following aircraft based on predictions of positions and strengths of aircraft wake vortices. This model has been a “jumping board” for the development of similar models, such as the TASS Derived Algorithms for Wake Prediction (TDAWP) and the Deterministic Two-Phase (D2P) model. This paper will describe these models and their intent of operation, as well as show comparisons with wake vortex measurements. Also described will be limitations to these models and future improvements.