Assessment of a Wake Vortex Retrieval Method Using Large-Eddy Simulations and a Lidar Simulator

Abstract Wake vortex studies using light detection and ranging (lidar) measurements constitute a decisive element for determining appropriate and efficient aircraft separations. Algorithms for characterizing the position and strength of wake vortices within lidar scans are available, for example, the radial velocity (RV) method. However, due to the lack of a ground truth from field measurements, no reliable accuracy bound for these algorithms could be given so far. Thus, we perform virtual lidar measurements via large-eddy simulation (LES) lidar simulators (LLSs) employing high-fidelity LESs of landing aircraft, where the position and strength of vortices is fully known. Lidar measurements are simulated to realistic detail by including spatial averaging along a line-of-sight and flow field distortions caused by the measurement geometry. Previous studies either focused on the wake vortex simulation or the lidar simulation, but never both aspects in full detail. Through simulations under various atmospheric conditions, the accuracy of the RV method can be defined as a 4% strength overestimation and 6% dislocation for vortices within an altitude range of below 2.5 initial vortex separations. Within a highly turbulent atmosphere, the RV method performs worse. The main driver of RV method inaccuracy is revealed as the lack of modeling mirror vortices, i.e., imaginary vortices caused by walls. This work enables rating the accuracy of studies by employing the RV method realistically. Furthermore, the LLSs allow generating a labeled dataset for evaluating further algorithms and developing new ones which may increase the data accuracy and thus reduce the effort of costly field measurements. Significance Statement When employing algorithms for characterizing wake vortices in light detection and ranging (lidar) field measurements, the truth is not known, such that the accuracy of these characterizations remains highly speculative. In this work, we therefore simulate wake vortices through high-fidelity simulations of landing aircraft, where the state of the wake vortices can be determined with high accuracy at any point in time. By furthermore virtually installing true-to-life lidars, we are able to obtain simulated lidar scans with an available ground truth. For the first time, these high-quality simulated scans allow evaluating the accuracy of characterization algorithms for wake vortices. Additionally, the simulations deliver a comprehensive labeled dataset of lidar scans for future studies.