Turbulence Coherent Structures Above Vertiports: Insights Into Unsteady Urban Aerodynamics

Safe and low noise operation of electric Vertical Take-off and Landing (eVTOL) vehicles in Advanced Air Mobility (AAM) corridors depends critically on accurate characterization of turbulence and coherent gust structures above rooftop vertiports in urban environments. This study employs large eddy simulations (LES) of flow around a wall-mounted square cylinder with aspect ratio 7, representing a simplified building and vertiport configuration at Re = 12,000, to investigate the dominant coherent structures above the rooftop. The WALE subgrid scale model is implemented in OpenFOAM and a grid refinement study is conducted to assess the sensitivity of mean and unsteady statistics to mesh resolution. Spectral Proper Orthogonal Decomposition (SPOD) is applied to moderate resolution cases to extract energetically dominant modes, while Fast Fourier Transform (FFT) analysis on finer grids resolves high frequency shear layer dynamics over the vertiport at manageable computational cost. The results reveal a combination of low frequency wake modes associated with cellular vortex shedding and a robust high frequency shear layer structure near St ≈ 5 that persists across the vertiport region and strongly contributes to the local gust environment. In particular, FFT spectra at a representative mid vertiport location indicate strong multi-component turbulence intensities of approximately 33.0%, 26.1%, and 24.1% in the streamwise, wall-normal, and cross-directional components of velocity, respectively. Comparison among grids with approximately 5–9 million and O (40) million cells shows that moderate resolution meshes are sufficient to capture the key spectral content and turbulence intensities in the mid vertiport region. The resulting physics based description of vortical structures and their spectral signatures above a canonical vertiport provides a foundation for reduced order gust models and turbulence aware design tools for eVTOL operations in complex urban canyons.