SPOD analysis of data-assimilated volumetric flow measurements of a quadcopter in hover flight

Spectral Proper Orthogonal Decomposition (SPOD) is applied to high-fidelity experimental velocity data of a quadcopter in hover to extract coherent flow structures. The dataset was obtained using Shake-The-Box Lagrangian particle tracking (Wolf et al., Experiments in Fluids, 2024) on a full-scale DJI Mavic drone operating outside ground effect. Although the drone is in hover mode, control action introduces unknown, transient rotor dynamics that complicate the flow field. SPOD reveals robust and interpretable coherent structures, which are further investigated using the frequency-time framework introduced by Nekkanti (Nekkanti, Journal of Fluid Mechanics, 2021) to analyze the transient phenomena in the dataset. The combined approach demonstrates the capability of SPOD and frequency-time methods to characterize complex flows in real-world flight conditions.