Multirotor Drone Aerodynamic Interaction Investigation

Abstract

Aerodynamic interactions between rotors are important factors affecting the performance of in-plane multirotor Unmanned Air Vehicles (UAVs) or drones, which are the majority of small size UAVs (or mini-drones). Optimal design requires knowledge of the flow features. The low Reynolds number of many UAV rotors raises the question of how these features differ from those expected by traditional analytical methods for rotorcraft. Aerodynamics of a set of side-by-side rotors in hover over a range of rotor separation and Reynolds number is studied using high-speed Stereo Particle Image Velocimetry (SPIV) and performance measurements. The instantaneous and time-averaged SPIV data presented here indicate an increase in inter-rotor wake interactions with decrease in rotor spacing and Reynolds number. A dip in rotor efficiency at small rotor spacing at low Reynolds number is observed through thrust and torque measurements. The basic components of in-plane multirotor wake and velocity profiles are identified and discussed to help generalize the findings to a wide range of drones. However, the data provide confidence in traditional analysis tools, with small modifications.

Numerical Characterisation of the Aeroacoustic Signature of Propeller Arrays for Distributed Electric Propulsion

“…Several concepts of DEP exist in the literature [11][12][13], but most of them are analysed for their applicability in designing BLI configurations [14,15]. Few studies have been conducted so far on the aeroacoustic properties of interacting propellers and are mainly related to counter-rotating propellers [16,17] and drones [18][19][20][21][22], where the distance between rotor hubs is a crucial aspect. In Reference [23], numerical aeroacoustic analyses of innovative propeller geometries have been carried out, accounting for a single propeller mounted on a wing.…”

Modeling Multirotor Aerodynamic Interactions Through the Vortex Particle Method

“…In contrast, distributed propulsion eVTOL aircraft are typically wing-borne during cruise, and the axes of rotation of the rotors are roughly aligned with the direction of flight, with the velocity of the aircraft adding directly to the axial inflow and advance ratio of the rotors. Even though previous studies have shown that multirotor interactions could drop the thrust performance by only a small amount [15][16][17]20 (∼4% relative to the isolated rotor), they also show that noise could be increased by as much as 3 dB, 18,19 corresponding to an acoustic signature two times more intense, which is a critical factor to consider in the design of urban mobility aircraft. Experimental results indicate that this increase in noise is directly related to unsteady loading during aerodynamic interactions.…”

“…11 and 12 is that a higher Reynolds number accentuates the negative interactions. The opposite was observed in an experimental study by Shukla et al, 16,17 which may indicate that this trend on Reynolds number is dependent on the specific rotor design being studied (the APC 10x7 is designed for high-Reynolds operation with a loading distribution gradually decreasing towards the blade tip, whereas Shukla et al used an untapered, untwisted blade highly loaded at the tip, designed for low-Reynolds testing and strong tip vortices).…”

“…Coaxial and tandem rotor interactions have been studied for decades in the rotorcraft community, meanwhile the side-by-side multirotor configuration has remained relatively unexplored. Recent experimental works [16][17][18][19][20] have studied the counter-rotating configuration where neighboring rotors spin in opposing directions (clockwise versus counterclockwise), however, no attention has been given to the co-rotating configuration where neighboring rotors spin in the same direction (both clockwise, or both counterclockwise). Also, these studies only considered the hovering case, meanwhile the effects of multirotor interactions in forward flight remain unexplored.…”

Neural-Swarm: Decentralized Close-Proximity Multirotor Control Using Learned Interactions

“…The interaction between two rotor blades has been studied in a lab setting to optimize the placement of rotors on a multirotor [17]. However, it remains an open question how this influences the flight of two or more multirotors in close proximity.…”