Numerical and experimental characterization of aft - fan noise for isolated and installed configur ations

The main objective of this paper is the characterization of the fan noise radiated in the aft direction for a coaxial turbofan installed in RFN (Rear Fuselage Nacelle) position. The challenge is to validate a numerical hybrid methodology, which has been developed for several years by Onera and Airbus, to provide the acoustic far field in the presence of the aircraft. This activity refers to the NACRE European project, in which a dedicated isolated/installed fan noise experiment was conducted with an aircraft model and a Turbine Powered Simulator (TPS). The numerical approach combines near field CAA computations, achieved by Onera with the sAbrinA-V0 solver, and farfield BEM computations achieved either by Airbus with the ACTIPOLE solver or by Onera with the BEMUSE solver. The fan noise source consists in azimuthal/radial modes of an infinite annular duct with uniform mean flow. All “cut-on” modes are computed individually, and then the un-correlated mode contributions are summed with amplitudes derived from measurements performed inside the by-pass duct with a circular array of pressure sensors. It is shown that the simulation of the internal propagation must take into account the three-dimensional geometry of the bypass duct, including the bifurcation, to explain the strong azimuthal oscillations of the RMS pressure inside and outside the TPS. Onera and Airbus’s BEM solvers are used to compute the installation effects generated by the rear part of the aircraft equipped with an H-tail plane. The agreement between both solvers is excellent, and the comparison with the experiments is satisfying.