Numerical Study on Jet-Like Outwash Induced by Multi-Rotor eVTOLs and Engineering Approaches for Outwash Mitigation

Abstract

This study presents a comprehensive computational investigation of outwash phenomena generated by electric vertical takeoff and landing (eVTOL) aircraft, with particular emphasis on how rotor geometry and alignment shape hazardous airflow patterns at vertiports. Using nondimensional Reynolds-averaged Navier-Stokes (RANS) simulations with the k-omega SST turbulence model implemented in OpenFOAM, the research systematically characterizes jet-like outwash across a range of multi-rotor configurations. Results demonstrate that propeller count and inter-propeller spacing are primary determinants of outwash intensity, orientation, propagation range, and boundary-layer structure. For power-lift eVTOLs, low propeller counts combined with narrow spacing produce highly directional, intensified jet-like outwash with propagation ranges far exceeding current FAA EB105a safety standards. Conversely, higher propeller counts and larger spacings reduce peak velocities and propagation distances, enabling safer and more compact vertiport layouts. High-propeller-count designs further exhibit vertically stratified and thickened outwash boundary layers, requiring tailored mitigation strategies. Targeted engineering solutions-such as modular blast deflectors aligned with predicted outwash directions-are shown to reduce required vertiport safety areas by up to 82% without compromising operational safety. These findings establish a direct link between aircraft design, regulatory compliance, and infrastructure optimization, offering practical pathways for safe and scalable urban air mobility. The study also provides a foundation for future research on optimal mitigation device geometries and system-level integration of eVTOL operations within urban environments.