Energy Consumption Modelling of Coaxial-Rotor in Vortex Ring State for Controllable High-Speed Descending

The ability to fast climb and descend is crucial for Unmanned Aerial Vehicle (UAV) applications in the moun- tains. The slower descent speed will affect the UAV’s working efficiency in reaching the rescue area. However, during the fast descent of the rotorcraft, a chaotic flow field rampages as the rotorcraft falls into its wake flow. This is known as the vortex ring. Therefore, the safe descent velocity of consumer UAVs is usually limited to approximately 3m/s. This limitation reduces the potential of UAVs to execute tasks in mountainous and plateau regions. To broaden the task capability constrained by the maximum descending speed, it is necessary to jointly analyze the flow field and the energy consumption during descending. Existing research mainly focused on how to avoid entering the vortex ring instead of offering sufficient power to fly with it. In this paper, in order to achieve an efficient rotorcraft for rescuing in mountainous and plateaus, we break through the maximum-descending-speed of a coaxial rotors UAV. Hence, a power consumption managing pipeline is pro- posed to extend the power tolerance of the UAV. Specifically, a theoretic model for the coaxial rotors is proposed to analyze the induced velocity and energy consumption during vertical descending. Then, the theoretic model is verified to be consistent with the Computational Fluid Dynamics (CFD) and wind tunnel experiment results. Finally, we optimized the tolerance of the power and dynamic system according to the theoretic model. With this pipeline, our real-time flight achieved 8m/s controlled vertical-descent-speed (CVDS), which is a leading result in both quadrotors and coaxial UAVs.