Active and passive vortex wake mitigation using control surfaces

Aircraft trailing vortices constitute a hazard to following aircraft and are therefore one of the main concerns for airport capacity constraints. At the Institute of Aerospace Engineering (ILR) experiments on wake vortices are conducted in a towing tank using particle image velocimetry. The motivation behind the presented investigations is the alleviation of the rolling moment induced on following aircraft using control surfaces of the preceding aircraft. An unstable vortex system is generated by the use of control surfaces. The instabilities lead to a mitigation of the vortex system. A variety of outboard flaps are used in preliminary studies to estimate the sizing and deflection of ailerons that lead to a vortex system with strong cooperative instabilities and thus to an alleviation of the rolling moment induced on following aircraft. In subsequent experiments a rectangular wing is equipped with preset ailerons, producing an unstable vortex system in its wake. The instabilities are excited by oscillating the ailerons. Each half-wing is equipped with two adjacent ailerons that oscillate in counter-phase in order to minimise fluctuations of the lift coefficient.