Optimization of open counter – rotation fan blades on the basis of solving a 3D Navier-Stokes inverse problem with the aim of reducing tonal noise

The paper presents some results of gas-dynamic and aero-acoustic optimization of the blade profile of an unducted counter-rotation fan (CRF) by using a 3D inverse problem. It was established on the basis of unsteady-state 3D Navier-Stokes equations that the interaction of tip vortices of the first and second rotors as well as potential interaction of the rotors is one of the key sources of tonal noise. Using the 3D solver of the inverse problem, aerodynamic loads are redistributed along the height of the blades of R1 and R2 rotors so as to reduce tip vortex intensity and potential rotor interaction in case of possible increase of the CRF thrust. To check the acoustic characteristics of the modified CRF, tonal noise modeling was carried out for the original and modified CRFs using CIAMs aero-acoustic 3DAS solver for the solution of unsteady-state equations. The near acoustic field and directivity diagrams in the far field were found. The fan tonal noise in take-off and landing was decreased by 4 dB without any thrust or efficiency losses