Engine Jet/Vortex Interaction in the Near Wake of an Airfoil

Abstract

*† ‡ Experimental results concerning the engine jet/vortex wake interaction will be presented. A method is described that improves the evaluation of unsteady vortex measurements and allows to analyze the effect of unsteady vortex movement. The results indicate that the engine jet modifies the stability properties of the wake flow. Depending on the engine position and operation mode the mean wandering amplitudes and the velocity fluctuations in the vortex wake are different and the topology of the vortex is affected. The current results suggest that for high-lift configurations the preferable engine position is closer to the wingtip if the focus is on the stability properties of the vortex wake. I. Introduction IRCRAFT separation rules in international aviation are a growing handicap for the ongoing rise in passenger numbers. To reduce the distance between following aircraft the physics of trailing vortices needs to be investigated. It is still a matter of scientific research to understand the mechanisms that can lead to a rapid decay of the vorticity strength. Since three decades in international civil air transportation the separation distances between flying aircraft are prescribed by rules, which divide the air fleet into different weight categories. The ICAO rules, for example, are based on three categories, below 7 tons maximum take-off weight, between 7 and 136 tons take-off weight, and more than 136 tons. The definition of these rules reaches back to flight tests in the early seventies, when the problem of wake vortex hazard first became apparent with the introduction of the Boeing B747. Since then the passenger numbers are continuously rising and forecasts from IATA, Boeing, or Airbus predict that this rise will go on. Major airports are reaching their capacity limits and this causes delays for airlines and passengers. The economic drawback of these delays urges to raise airport capacities by increasing the number of take offs and landings per time. However, this necessitates a revision of the current vortex wake related separation standards. That is, new aircraft separation rules have to be derived that at least keep or even improve the current safety level of international air transportation. This corresponds to the question, which safety margins exist in the current spacing. The answer to this question needs to be based on detailed knowledge about the physics of aircraft wakes, since even under today’s conditions there are nearly daily vortex encounters 1