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Published March 2022 | Published + Supplemental Material
Journal Article Open

Parametric study of small-scale rotors in axial descent

Abstract

Despite extensive research in multirotor aerodynamics in the recent past, axial descent, specifically the vortex ring state, still poses great challenges for multirotor configurations as this flight stage is typically accompanied by severe losses in rotor thrust and strong thrust fluctuations. This paper presents a parametric study to investigate the influence of relevant geometric parameters of a small-scale rotor blade on the rotor performance in axial descent. Design variables subject to variation were the collective pitch, chord length, taper ratio, number of blades, as well as the tip geometry. Custom rotors for each parameter modification were manufactured and experimentally evaluated in wind tunnel tests with mean thrust recordings and measurements of the thrust fluctuations serving as performance metrics. Results indicated that rotor blades with larger aspect ratio and higher blade loading coefficient are less affected by the adverse aerodynamics in the vortex ring state, experiencing lower thrust losses and vibrational loads. Particle image velocimetry flow visualization confirmed that the aerodynamic losses in the vortex ring state can be attributed to blade vortex interactions. Comparison of the rotor flow structure in hover of all investigated rotor designs suggested that improvements in the descent performance of a rotor stem from a combination of reduced tip vortex strength and increased axial tip vortex convection rate. Using the experimental findings of this study, a predictive model for approximating the maximum extent of mean thrust losses in axial descent for a given blade geometry and hover thrust coefficient could be established.

Additional Information

© 2022 Author(s). Published under an exclusive license by AIP Publishing. Submitted: 29 December 2021 . Accepted: 25 February 2022 . Published Online: 17 March 2022. This research was funded by the Center of Autonomous Systems and Technology (CAST) and the Summer Undergraduate Research Fellowship (SURF) at the California Institute of Technology. DATA AVAILABILITY. The data that support the findings of this study are available from the corresponding author upon reasonable request. The authors have no conflicts to disclose.

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Published - 035124_1_online.pdf

Supplemental Material - supplementary_material.pdf

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Additional details

Created:
October 9, 2023
Modified:
October 24, 2023