High-fidelity Simulations of Rotors in Compact Configuration

Abstract

High fidelity CFD simulations of seven rotors in compact configuration at three different flight scenarios are performed. The cases are hover, as well as 50 km/h and 100 km/h forward flight. For comparison each rotor is simulated isolated with the same RPM and pitch angle as in the configuration. Additionally, a bigger isolated rotor with the same area as the complete configuration is simulated. For the configuration as well as the bigger rotor a flight mechanic trim is performed using the flight mechanic tool VFAST. The CFD simulation is performed with FLOWer. In hover, only the center rotor showed a significant Figure of Merit (FM) drop 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 gain of the front rotors is reduced to 3%-11% and the decrease to 5%-9%. Due to the higher pitch the wake of the rotors flows away from the rotor plane and the rotor-rotor interactions are reduced.