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1. Rotor-on-Rotor Aeroacoustic Interactions of Multirotor in Hover

   Alvarez, E. J.; Schenk, A.; Critchfield, T.; and Ning, A. (July 2020, Journal of the American Helicopter Society)

   Multirotor configurations introduce complicated aerodynamic and aeroacoustic interactions that must be considered during aircraft design. In this paper we explore two numerical methods to model the acoustic noise caused by aerodynamic rotor-on-rotor interactions of rotors in hover. The first method uses a conventional mesh-based unsteady Reynolds-average Navier-Stokes (URANS) solver, while the second consists of a meshless Lagrangian solver based on the viscous vortex particle method (VPM). Both methods are coupled with an aeroacoustics solver for tonal and broadband noise predictions. Noise predictions are validated for single and multi-rotor configurations, obtaining with the VPM a similar accuracy than URANS while being two orders of magnitude faster. We characterize the interactions of two side-by-side rotors in hover as the tip-to-tip distance and downstream spacing are varied. At an observer located six diameters away, multirotor noise is the strongest above and below the rotors, increasing by about 10 dBA directly underneath as the rotors are brought closer together. The interactions show no sensitivity to blade loading distribution, indicating that multirotor interactions are not alleviated with a lighter tip loading. We found that noise can be mitigated by spacing the rotors in the downstream direction—with the optimal spacing being about half a diameter—achieving a noise decrease of about 4 dBA without any aerodynamic penalties. 

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2. Rotor-on-Rotor Aeroacoustic Interactions of Multirotor in Hover

   Alvarez, E. J.; Schenk, A.; Critchfield, T.; and Ning, A. (July 2020, Journal of the American Helicopter Society)

   Multirotor configurations introduce complicated aerodynamic and aeroacoustic interactions that must be considered during aircraft design. In this paper we explore two numerical methods to model the acoustic noise caused by aerodynamic rotor-on-rotor interactions of rotors in hover. The first method uses a conventional mesh-based unsteady Reynolds-average Navier-Stokes (URANS) solver, while the second consists of a meshless Lagrangian solver based on the viscous vortex particle method (VPM). Both methods are coupled with an aeroacoustics solver for tonal and broadband noise predictions. Noise predictions are validated for single and multi-rotor configurations, obtaining with the VPM a similar accuracy than URANS while being two orders of magnitude faster. We characterize the interactions of two side-by-side rotors in hover as the tip-to-tip distance and downstream spacing are varied. At an observer located six diameters away, multirotor noise is the strongest above and below the rotors, increasing by about 10 dBA directly underneath as the rotors are brought closer together. The interactions show no sensitivity to blade loading distribution, indicating that multirotor interactions are not alleviated with a lighter tip loading. We found that noise can be mitigated by spacing the rotors in the downstream direction—with the optimal spacing being about half a diameter—achieving a noise decrease of about 4 dBA without any aerodynamic penalties. 

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3. Altitude Control of a Tethered Multi-Rotor Autogyro in 2-D Using Pitch Actuation via Differential Rotor Braking

   https://doi.org/10.23919/ACC55779.2023.10155811  

   Noboni, Tasnia; McConnell, Jonathan; Das, Tuhin (May 2023, Proceedings of the American Control Conference)
4. Guest control of a hydrogen bond-catalysed molecular rotor

   https://doi.org/10.1039/C7CC07672J  

   Rushton, Gregory T.; Vik, Erik C.; Burns, William G.; Rasberry, Roger D.; Shimizu, Ken D. (January 2017, Chemical Communications)

   Herein, the control of a molecular rotor using hydrogen bonding guests is demonstrated. With a properly positioned phenol substituent, the N -arylimide rotors can form an intramolecular hydrogen bond that catalyses the rotational isomerization process. The addition of the guests disrupts the hydrogen bond and raises the rotational barrier, slowing the rotation by two orders of magnitude. 

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5. A High Torque Density Halbach Rotor Coaxial Magnetic Gear

   Hong, H Y; Bird, J Z; Barnett, D; Williams, W. (January 2019, IEEE International Conference on Electrical Machines and Drives)

   This paper presents the design, analysis, and experimental testing results for a 5.67:1 Halbach rotor magnetic gearbox with a ferromagnetic back support. Using 3-D finite element analysis software the Halbach magnetic gearbox was calculated to achieve a volumetric torque density of 284N·m/L with only an active region outer diameter of 120mm. The experimental prototype obtained an active region volumetric torque density of 261.4N·m/L 

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