Interaction of a Three-Dimensional Counter-Rotating Vortex Pair with a Dynamically Perturbed Ground Plane

Counter-rotating vortex pairs (CRVPs) are unavoidably produced by fixed-wing aircraft during flight. The pressure difference between the underside and topside of the wing drives flow around the wingtips, which roll up into discrete vortices behind the aircraft. This CRVP then descends downwards due to its self-induced velocity. The steep velocity gradients present in the vortex cores may impose unexpected rolling moments on, or even damage, following aircraft. This hazard is especially dangerous in terminal phases of flight such as takeoff and landing, as pilots often have insufficient altitude to recover. Currently, this hazard is mitigated by the FAA through operational separation guidelines, which rely on known aircraft weights and wingspans. In contrast to commercial airports, naval aircraft operating off aircraft carriers must also contend with a dynamic oceanic free surface featuring high-amplitude waves. Understanding how this dynamic environment interacts with CRVPs is therefore crucial to improving the safety of aircraft carrier operations. To investigate this experimentally, a CRVP is generated in a quiescent towing tank facility via a towed delta wing. This CRVP, which features a non-zero angle of descent and both axial and circumferential flow, descends towards a dynamically actuated ground plane (DGP). This DGP is capable of generating controlled dynamic standing-wave perturbations, representative of the oceanic free surface. Particle Image Velocimetry (PIV) is used to quantify the rate of CRVP decay and track the trajectory of the vortex cores, while laser-induced dye fluorescence renders visible the 3D topological changes and secondary vortex structures (SVS) resulting from the wall interaction. An exploration of ground-perturbation amplitudes and frequencies is performed to identify potential interaction regimes as well as identify optimal disturbance frequencies, with the aim of promoting CRVP decay. This increased understanding of how dynamic perturbations induce topological changes and alter decay rates will inform future aircraft carrier operations.