Turbofan Interaction Noise Reduction Using Trailing Edge Blowing: Numerical Design and Assessment and Comparison with Experiments

This paper investigates the effect of a flow control device on turbofan sound generation, applied to a low-speed axial compressor model in a laboratory test rig. This treatment consists in a secondary mass flow ejected through the trailing edge of the rotor blades, designed to fill the velocity defect behind the rotor and to decrease the turbulent kinetic energy related to the wakes, so that broadband interaction noise should be reduced. The design and implementation of the blowing device is first briefly described, as well as the fan stage experiment. Then, the paper focuses on computation methods devoted to the capture of turbulent wakes and to the acoustic response of the stator (with and without blowing). 3D steady RANS and quasi-2D LES approaches are considered for the CFD, both coupled to an integral formulation based on the theory proposed by Amiet, aiming at calculating the in-duct sound power and estimating the acoustic performance of the treatment. Under optimal blowing conditions, significant sound power reductions are predicted by the simulations. First attempts to relate numerical predictions to available measurements, i.e., hot-wire data and in-duct sound power spectra, are proposed and discussed.