High-Fidelity Simulations of Rotors in a Compact Configuration

High-fidelity computational fluid dynamics (CFD) simulations of seven rotors in compact configuration at three different flight scenarios are performed. The cases are hover as well as 50 and 100 km/h forward flights. For comparison, each rotor is simulated as an isolated rotor with the same RPM and pitch angle as in the configuration. Additionally, a bigger isolated rotor with the same diameter as the complete configuration is simulated. For the configuration as well as the bigger rotor a flight mechanics trim is performed using the flight mechanics tool VFAST. The CFD simulations are performed with FLOWer. In hover, only the center rotor showed a significant figure of meritdrop of 16% compared to the isolated rotor. The thrust of the outer rotors is increased at the tip areas facing outwards, while the tip areas towards the center and the tip areas of the center rotor showed reduced thrust compared to the isolated rotor. The wake contraction at the outer rotors is increased compared to the bigger rotor. For the 50 km/h forward flight, the efficiency of the front rotors is increased (10-17%) and the rear ones decreased (11-16%). In this case, the wake is directly convected from the front rotors into the rear rotor planes and strong vortex interactions occur. For the 100 km/h case, the efficiency of the front rotors increases by 3-11%, while it decreases by 5-9% for the rear rotors. Due to the higher pitch, the wake of the rotors flows away from the rotor plane and the rotor-rotor interactions are reduced.