Rotor–duct aerodynamic and acoustic interactions at low Reynolds number
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Ducted single and multi-rotor UAVs (unmanned aerial vehicle) offer better crash worthiness and safety compared to open rotor UAVs. The interactions that affect performance and acoustics are of interest. High speed stereo particle image velocimetry (SPIV), performance, and acoustic measurements were done on a rotor with removable protective duct to study rotor–duct aerodynamic interactions over a range of hover conditions at low Reynolds number. Instantaneous and averaged SPIV velocity field and performance results, as well as acoustic signatures, are compared to baseline un-ducted rotor cases. Increase in rotor figure of merit is strongly correlated with the level of duct interaction with rotor tip vortex cores. Efficiency change is higher for the cases where thrust induced losses take a larger share of the overall aerodynamic losses. While the overall acoustic sound pressure level was not affected significantly, cases with higher vortex core/duct interactions showed higher tonal content.
This research was partially funded by the Government Vertical Lift Rotorcraft Centers of Excellence, under Agreement no. W911W6-17-2-0002. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. The U.S. Government technical monitor is Mahendra Bhagwat. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Aviation Development Directorate or the U.S. Government. We would also like to thank Dr. Nandeesh Hiremath for his help in acoustic tests and the team of undergraduate researchers in the Experimental Aerodynamics lab at Georgia Tech for their assistance in building the setup and tests.
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