Investigation of Near Ground Effects in Hover Flight for the Multi-Rotor Aircraft Volocopter-2X

High-fidelity CFD simulations of hovering flights of the multi-rotor Volocopter 2X (VC2X) aircraft with three different heights above the ground and an out of ground reference case are presented. The tool chain applied consists of the CFD solver FLOWer, which is loosely coupled to the flight mechanic tool VFAST. For all simulations an adequate representation of the flight mechanics is of crucial importance since the high number of trim degrees of freedom of the VC2X has a significant influence on the flight physics. A short introduction and validation of VFAST is carried out, which shows that VFAST already provides valuable stand-alone results for the considered flight envelope. The in ground and out of ground CFD simulations showed a highly complex flow field for the VC2X. With increasing ground proximity the number of vortex structures induced by the ground increases and the rotor wake is characterized by strong fluctuations. Basic rotorcraft in ground effect phenomena, like a high-pressure area below the rotor plane and aircraft power reduction are observed for low flight heights. The decreased power requirement is mainly traced back to a decrease of the airframe download. The system figure of merit for all three in ground cases merely changes.