Numerical Investigation on Influence of Fuselage on Multirotor Wake Vortex Structures in Forward Flight

Abstract

With the increase interest in utilizing multirotor UAS in very low altitude airspace, the safety aspect associated with higher UAS density gains importance. One of the safety consideration is the separation requirements for UAS sharing the airspace, which consists of two major components: wake-based and CNS performance-based. To evaluate the wake-based separation requirements, the wake-field produced by the leading UAS and the resulting encounter response by the follower UAS must be obtained. While previous studies on aircraft wake vortex evolution showed that the fuselage wake have small impact on the overall wake vortex strength and structures, the more distributed lift generation with less distance between the initial formation point of wake vortex to the fuselage could lead to a larger impact. This paper investigates the impact of including multirotor fuselage on simulating the strength and structure of the resulting wake vortex.

Comparison of Small Multirotor Wake Vortex of Different Weight Class and Rotor Configurations via Numerical Simulation

“…Comparing to helicopters, current generation of small multirotor UAS generally utilize fixed-pitch propeller with variable speed motors; larger passenger carrying multirotor, on the other hand, could include variable pitch propeller in their design [21,22]. Experimental and simulation studies have shown inter-rotor gap could significantly affect the overall lift generation by quadrotors [23][24][25], though the propeller-to-propeller interaction appears to be reduced when an appropriately sized vehicle fuselage is included [26,27]. When in forward flight, studies have shown that the wake generated by the forward propeller pair in quadrotors would be ingested by the rear propeller pair (e.g.…”

“…Similar process was also used in Refs. [32] and [27] to investigate the long-term evolution and impact of fuselage model inclusion, respectively. The simulations were carried out in two parts, the RANS turbulence modeling for near-field wake generation and the LES turbulence modeling for far-field wake generation.…”