Extension of the Analytic Vortex Ring State Model for eVTOL Application

The engineering model determining the onset of Vortex Ring State (VRS) was applied to eVTOL aircraft, and the effect of different landing trajectories and aircraft drag was investigated. Next, the new model to compare the VRS susceptibility according to the different blade geometries and trajectories is proposed by extending Ahlin & Brown's model to incorporate the two-dimensional thrust and inflow distribution on the rotor disc. For validation, two different trajectories crossing the boundary of the onset of the VRS were simulated, and the results were compared with the Vorticity Transport Method (VTM). Furthermore, the disturbance distribution of moderately and highly twisted blades are compared. The extended model can capture the physical phenomena by the distribution of the disturbances and reflect the effect of blade geometries and trajectories. It is essential to investigate the model further through a correlation analysis using experiments or numerical analysis.