Unsteady Aerodynamic Loads on a High-Agility Aircraft due to Wake Vortex Encounter

Abstract

The presented investigation focuses on the determination of unsteady aerodynamic loads for different kinds of wake vortex encounters. The wake-generating aircraft is a delta–canard configuration, whereas for the penetration, just a delta wing is considered. Based on extensive experimental and numerical investigations of the wake vortex system of a preceding aircraft, the wake-induced angle of attack on an encountering aircraft is determined. Therefore, the induced flowfield of the wake-generating aircraft is transformed into the coordinate system of the penetrating aircraft. Because the unsteadiness results on the one hand from the velocity fluctuations inside the wake, and on the other hand from the relative movement of the two aircraft, the wake problem is split into a discrete and a continuous wake problem. Both problems lead to an unsteady distribution of the angle of attack, which is variable in the chord and spanwise directions. The resulting lift and pitching moment distribution is calculated by an alternative approach to the unsteady lifting surface method. For the discrete wake problem, the resulting loads depend on the heading and bank angle of the penetrating aircraft relative to the vortex axes. In general, negative lift, rolling, and pitching moments can be observed. Their magnitude varies with the encounter maneuver. The continuous wake problem refers to the unsteady loads due to velocity fluctuations inside the wake on an aircraft following the wake-generating aircraft. Thereby, high-frequency forces and moments act upon the following aircraft.