Low-Speed Aerodynamics and Aeroacoustics of CROR Propulsion Systems

Contra Rotating Open Rotor (CROR) propulsion systems have come back into focus as a possible economic and environmentally friendly powerplant for future transport aircraft. Having been widely applied to the simulations of single rotation propellers, the DLR CFD code TAU and the aeroacoustic analysis tool APSIM have been employed for the analysis of the complex aerodynamics and aeroacoustics of this type of aircraft propulsion system. In order to demonstrate the codes applicability to these types of simulations as well as to develop an understanding of the impact of configuration variations, a generic 8x8 and 10x8 pusher CROR powerplant are studied here at typical sea-level take-off conditions of M = 0.2. The results allow for a detailed analysis of the aerodynamic interactions between the two rotors as well as the noise generation mechanisms, allowing for an improved un-derstanding of interaction tone sources. In addition, the impact of the numerical approach to the aeroacoustic simulations on the results is studied with a focus on determining the importance of the quadrupole contributions. Nomenclature α Angle of attack, [◦] β75 Blade pitch angle at 75 % radius, [◦] η Rotor efficiency, [-], η = CT /Cl · J/(2Π) ψ Azimuth angle, [◦] ρ Density, [kg/m3] Θ Polar angle, [◦