In-flight simulation of wake encounters using deformed vortices

Abstract

During the decay process the shape of wake vortices changes significantly which has an influence on the encounter characteristics, hence on the encounter hazard. In order to evaluate the influence of vortex deformation on the wake encounter hazard, in-flight simulations with the DLR research aircraft ATTAS were carried out. For a realistic analysis of wake encounters flow fields of matured vortices were generated with large eddy simulations. These flow fields were used for the determination of histories of induced forces and moments acting on the wake encountering aircraft. The force and moment histories were then fed into the equations of motions of the non-linear six degree-of-freedom in-flight simulation of the DLR research aircraft ATTAS. In order to compare different stages of vortex deformation, encounters were simulated in flight with wavy vortices and vortex rings. The most important benefit of the in-flight-simulation is the realistic environment, which enables a realistic assessment of pilots' encounter acceptance. The analysed scenario was of a wake encounter during final approach. The encounter conditions correspond to separation distances of about 4nm and 5nm behind an aircraft of the 'heavy' category. During the encounters the ATTAS was flown under manual control. Altogether 31 encounters were simulated in flight, 9 with wavy vortices and 22 with vortex rings.

How Plate Lines Influence the Hazard Perception of Pilots During Wake Encounters

“…This method was deemed feasible by Barrows [23], verified against wind tunnel tests by de Bruin [24], and further validated using real flight test data by Fischenberg [25] and Jategaonkar [26]. The method was applied in various studies in the past [27][28][29][30][31][32] and is accepted to provide vortex induced forces and moments of acceptable accuracy.…”

Simulation Study of Severity and Mitigation of Wake-Vortex Encounters in Ground Proximity

“…The method was applied in various studies in the past [33,[38][39][40] and is accepted to provide vortex induced forces and moments of acceptable accuracy.…”

“…For pilot-in-the-loop investigations with subjective pilot ratings as well as for offline simulation studies, jRCRj max has proven to be a suitable metric. Past studies showed that pilots accepted encounters below jRCRj max of 0.2 [38,39] during approach but out of ground effect. Below this value, the impact of the wake was not distinguishable from natural atmospheric turbulence.…”

Sensitivity Analysis of Aircraft Encounters with Deformed Wake Vortices (Invited)

“…In addition, the uncertainties in vortex modeling, i. e. whether to include wake deformation in safety assessments or to use a simple straight vortex pair, are assumed to be larger than the inaccuracies of highly sophisticated aircraft flight simulation models. Aircraft encounters with wavy vortices and vortex rings have been analyzed by means of offline simulations 12,13 and piloted tests in certified training and research flight simulators 14,15 or by in-flight simulation, 16 using either simplified models of the deformed vortices or three-dimensional fields of vortex-induced velocities from prior Large-Eddy Simulation (LES). Those studies indicate a reduced encounter severity for the vortex ring phase after linking.…”