Acoustic Simulation for Wing Mounted Open Rotor and Stator

Open Rotor and Stator (ORAS) propulsion systems are investigated as a potential successor to conventional turbofan engines due to their improved propulsion efficiency when a bypass flow being unconstrained by a nacelle. This type of propulsion system offers similar efficiency benefits as Contra-Rotating Open Rotor (CROR) configurations, while eliminating the main drawbacks associated with weight and complexity of the CROR. Acoustically, the configuration remains challenging since noise emission characteristics are influenced by installation effects due to mutual acoustic interactions with an airframe. In “Clean Sky 2”, the project partners Airbus, SAFRAN and DLR carried out CFD and CAA studies for a product-representative engine geometry and airframe. The aeroacoustic evaluation was performed for a take-off operation point based on an unsteady RANS coupled with a fast multipole boundary element method, where the most challenging part was separating the acoustic input from other non-acoustic vortex modes that are so heavily present in the URANS solution. The far-field SPL results that were evaluated on a spherical surface for dominant frequencies are presented in this paper for the purpose of understanding the noise directivity and levels produced by a full-scale ORAS-powered short-to-medium range aircraft prototype.