Risk Assessment Method for Encounters with Perturbed Wake Vortices

• Applicant: Professor Dr.-Ing. Robert Luckner
• Subject Area: Fluid Mechanics ; Traffic and Transport Systems, Intelligent and Automated Traffic
• Term: from 2010 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 179299766

With a few exceptions, risk analyses and severity assessments of aircraft wake vortex encounters have applied the simplified model of two counter-rotating straight vortices. In reality, aging vortices develop a wavy deformation that can lead to a breakup into vortex rings depending on the atmospheric conditions. Up to now, the consequences of this effect were usually neglected. However, in order to assess reduced minimum separation requirements and new concepts for a more efficient use of airspace, all mechanisms affecting the potential wake vortex hazard of trailing aircraft have to be regarded. The objective of this project is to investigate the impact of wake vortex deformation on the potential hazard for an encountering aircraft and to develop a methodology by which the deformation can be considered in wake turbulence related safety analyses. The central hypothesis is that wake deformation reduces the wake vortex risk and may contribute to a revision of today's separation minima that are considered conservative under many conditions. Thus, the activities of this project contribute to current research objectives to provide solutions for the growing capacity problem at major airports.Several important milestones were achieved during the previous project phase. Using 3D velocity fields, which were derived from large-eddy simulations (LES) of wake decay, real- and fast-time simulation models of deformed vortices were developed. They currently offer the highest modelling fidelity for wake vortex encounter simulations. They were used in flight simulators to investigate the impact of wake deformation on pilot's assessment of encounter severity as well as for initial Monte-Carlo Simulations (MCS) of wake encounters during landing approach. The results show that the axial encounter location has to be considered as an additional parameter to assess the impact of wake deformations. The project extension aims to finalize these activities with an assessment of the stated hypotheses. Current results show, that the wake deformation is well represented by the simplified analytical models. Research is still needed regarding the adaption of the vortex strength with increasing vortex age, as state-of-the-art wake vortex models only cover a 'global' circulation, whereas the 'local' circulation is required here. Encounters simulated with the high-fidelity LES velocity fields are used as reference for the validation of the vortex simulation models. The core of the analysis are MCS with considerably higher sample sizes that serve to answer the central question: Are deformed wake vortices less hazardous than straight vortices?

• DFG Programme: Research Grants