Vertical take-off and landing (VTOL) vehicle platforms with multiple small rotors are gaining importance for small Unmanned Aerial Vehicles (UAVs) as well as distributed electric propulsion for larger passenger or cargo carrying vehicles. These rotors operate in the low Reynolds number regime, unlike large rotors for which the existing prediction methods such as the Free Wake Model were developed. Operating at very low Reynolds number essentially means that the viscous effects are more dominant and propagate to significant spatial scales with respect to the rotor dimensions. This impacts the nature of inter-rotor aerodynamic interactions which become more difficult to predict. Inter-rotor interactions play an important role in rotor performance, vibrations, and noise generation. This necessitates the development of an interaction prediction capability to better aid the efforts of UAV developers; and any cost-effective prediction methodology would require knowledge of the interaction effects.

 

In the present work, two nominally identical commercial UAV rotors are studied at a range of rotor-to-rotor separations in hover and forward flight experimentally as well as computationally. The effort is in parallel with ongoing vehicle flight tests with 4 and 8 rotors UAV using identical rotors. This extends prior work on the rotors in isolation. The bi-rotor tests in tandem in-plane configuration were performed in Georgia Tech’s 2.13m x 2.74m test section wind tunnel for a range of wind tunnel and rotor speeds. The test conditions were also modeled and simulated using RotCFD solver, which uses a Navier-Stokes wake computation with low-Reynolds number blade section data.

 

In hover, the performance of the rotors is found to be more sensitive to the distance between rotors at low rotation speeds, becoming much less sensitive at higher rotation speeds. This indicates the presence of greater inter-rotor interactions at low Reynolds number conditions. Lower performance was observed in simultaneous operation than in isolation for both rotors. In forward flight tests, the rotor situated further downstream in the flow recorded lower performance than the upstream positioned rotor. Further ongoing comparisons between CFD and experimental results are expected to be completed well in time for the final paper.

 


Interactions of Two Uav Rotors at Low Reynolds Number

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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