The Structure of Merging Turbulent Jets Beneath a Small Quadrotor
Abstract
The downwash wake of a hovering quadrotor governs both the vehicle's own performance and the safe spacing of multi-rotor formations. Prior measurements have largely characterized the mean flow, using single-point anemometry, volumetric tracking, or planar cuts through part of the rotor system. Higher-order turbulent statistics of the merged wake, and how they relate to canonical jet scaling, have remained unresolved, particularly for small quadrotors at the low-Reynolds-number end of the size range. Here, we present a detailed particle image velocimetry (PIV) study of the downwash of a hovering Crazyflie 2.1 quadrotor (arm length, l = 46 mm), sampled along a diagonal cut, passing through rotors along the symmetry axis of the quadrotor, and a front-rotor cut, passing through adjacent rotors. The four rotor jets merge into a single column by z/l ≈ 5, beyond which the mean velocity profiles progressively approach the canonical round-jet self-similar form, collapsing by z/l ≈ 13 when scaled by the local centerline velocity and half-width. Centerline decay and half-width growth follow canonical scaling laws with an effective source diameter Deff = 2.29 l, effective Reynolds number ReDeff = 3 × 104, at the low end of the range over which canonical jet scaling has been established, and spreading and decay constants nonetheless within the canonical round-jet range. Resolving both cuts shows that the turbulent normal stresses retain a bimodal, cut-dependent signature of the four-rotor source throughout the measurement domain.
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BibTeX
@misc{kiran2026structure,
title = {{The Structure of Merging Turbulent Jets Beneath a Small Quadrotor}},
author = {Anoop Kiran and Nora Ayanian and Kenneth Breuer},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.30900},
eprint = {2608.30900},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.30900},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Structure of Merging Turbulent Jets Beneath a Small Quadrotor
AU - Anoop Kiran
AU - Nora Ayanian
AU - Kenneth Breuer
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2608.30900
UR - https://arxiv.org/abs/2608.30900
AB - The downwash wake of a hovering quadrotor governs both the vehicle's own performance and the safe spacing of multi-rotor formations. Prior measurements have largely characterized the mean flow, using single-point anemometry, volumetric tracking, or planar cuts through part of the rotor system. Higher-order turbulent statistics of the merged wake, and how they relate to canonical jet scaling, have remained unresolved, particularly for small quadrotors at the low-Reynolds-number end of the size range. Here, we present a detailed particle image velocimetry (PIV) study of the downwash of a hovering Crazyflie 2.1 quadrotor (arm length, l = 46 mm), sampled along a diagonal cut, passing through rotors along the symmetry axis of the quadrotor, and a front-rotor cut, passing through adjacent rotors. The four rotor jets merge into a single column by z/l ≈ 5, beyond which the mean velocity profiles progressively approach the canonical round-jet self-similar form, collapsing by z/l ≈ 13 when scaled by the local centerline velocity and half-width. Centerline decay and half-width growth follow canonical scaling laws with an effective source diameter D_eff = 2.29 l, effective Reynolds number Re_D_eff = 3 × 10^4, at the low end of the range over which canonical jet scaling has been established, and spreading and decay constants nonetheless within the canonical round-jet range. Resolving both cuts shows that the turbulent normal stresses retain a bimodal, cut-dependent signature of the four-rotor source throughout the measurement domain.
ER -