Wake interactions drive synchronized vortex merging in a hovering quadcopter
Abstract
The most energetic coherent structure of a hovering full-scale quadcopter is associated with a self-organizing process in which the individual rotor vortices synchronize their frequencies while undergoing merging events, yielding a globally correlated structure. We identify and characterize this phenomenon by applying spectral modal and conditional analyses to assimilated three-dimensional velocity data acquired via Shake-The-Box Lagrangian particle tracking. The dataset captures a high-Re, turbulent flow further complicated by time-varying rotor speeds stemming from active flight control, low-frequency vehicle drift, finite spatio-temporal resolution, and measurement uncertainty. Most coherent structures recover established single-rotor features such as tip vortices and their subharmonic pairing. The globally synchronized vortex merging manifests as a spectral peak at an incommensurate frequency below the rotor band, which cannot be explained by single-rotor aerodynamics, subharmonic instabilities, or band-to-band triadic interactions. Instead, conditional averaging provides evidence of the aforementioned intermittent, distinctly non-subharmonic vortex-merging process involving all four rotor wakes. Establishing whether or not this phenomenon is observed across different flight conditions and configurations remains speculative; however, the consistent characterization of the globally synchronized vortex merging using complementary frequency- and time-domain analyses despite experimental complexities, in particular rotor speed variations, demonstrates its robustness.
Related
- A Universal Vortex-Formation Law for Insect Hovering
- Blade secondary vortex interaction noise in hovering rotors
- The Nonlinear Physics and Statistical Field Theory of Twilight Clouds: Hovering Dynamics and Dynamic Inertia Emergence
- Synchronized Spin Trajectories under Collective Weak Measurements
- On the Complexity of Level-Synchronized Tree Automata for Quantum Circuit Verification
BibTeX
@misc{pratschke2026wake,
title = {{Wake interactions drive synchronized vortex merging in a hovering quadcopter}},
author = {Elias S. Pratschke and Claus C. Wolf and Daniel Schanz and Andreas Schröder and Oliver T. Schmidt},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19507},
eprint = {2609.19507},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19507},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Wake interactions drive synchronized vortex merging in a hovering quadcopter
AU - Elias S. Pratschke
AU - Claus C. Wolf
AU - Daniel Schanz
AU - Andreas Schröder
AU - Oliver T. Schmidt
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.19507
UR - https://arxiv.org/abs/2609.19507
AB - The most energetic coherent structure of a hovering full-scale quadcopter is associated with a self-organizing process in which the individual rotor vortices synchronize their frequencies while undergoing merging events, yielding a globally correlated structure. We identify and characterize this phenomenon by applying spectral modal and conditional analyses to assimilated three-dimensional velocity data acquired via Shake-The-Box Lagrangian particle tracking. The dataset captures a high-Re, turbulent flow further complicated by time-varying rotor speeds stemming from active flight control, low-frequency vehicle drift, finite spatio-temporal resolution, and measurement uncertainty. Most coherent structures recover established single-rotor features such as tip vortices and their subharmonic pairing. The globally synchronized vortex merging manifests as a spectral peak at an incommensurate frequency below the rotor band, which cannot be explained by single-rotor aerodynamics, subharmonic instabilities, or band-to-band triadic interactions. Instead, conditional averaging provides evidence of the aforementioned intermittent, distinctly non-subharmonic vortex-merging process involving all four rotor wakes. Establishing whether or not this phenomenon is observed across different flight conditions and configurations remains speculative; however, the consistent characterization of the globally synchronized vortex merging using complementary frequency- and time-domain analyses despite experimental complexities, in particular rotor speed variations, demonstrates its robustness.
ER -