Approches analytiques et numeriques pour la prediction du bruit tonal et large bande de soufflantes de turboreacteurs

In a modern high bypass ratio turbofan engine, the fan stage significantly contributes to the acoustic energy radiated by an aircraft at approach conditions. This research project takes place in the framework of improving prediction methods for tonal and broadband noise created by the rotor-stator interaction in a fan stage in order to provide tools for quieter designs of aircrafts.;A literature review leads to the choice of two approaches for the fan noise prediction. On the one hand, analytical models taking into account cascade effects are designed for parametrical studies in an industrial context although they use several simplifying hypotheses. On the other hand, numerical methods allow considering realistic configurations but are computationally demanding. Thus the original objectives of this work consist in evaluating cascade based acoustic models, in proposing modifications to improve their reliability, and in developing a new numerical method for turbomachinery noise. The latter is based on unsteady compressible aerodynamic simulations to directly compute acoustic sources that are then radiated with an acoustic analogy.;For tonal noise studies, unsteady flow simulations using Reynolds-Averaged Navier-Stokes equations (URANS) are performed on simplified rotor-stator configurations as well as on a realistic axial compressor stage. The deterministic acoustic sources created by the rotor wake interaction with the downstream stator vanes are correctly resolved, allowing the application of the numerical method. A cascade analytical model is improved in order to introduce a better decomposition of the excitation as well as vane camber effects in the acoustic sources prediction. These improvements are validated by comparisons with the results of the numerical method. The vane thickness is also seen to have a second order effect. Finally the developed numerical method is shown to be very efficient for tonal noise prediction with a distribution of sources following the mean vane camber line since the fully 3D effects of the stator response and of the vane geometry are included.;In the broadband noise context, three cascade based analytical models are evaluated and compared to an isolated airfoil model on two realistic test cases. Cascade effects are found to play a major role both on the acoustic sources and on the acoustic power over the frequency band for overlapping vanes. A model including a tri-dimensional cascade response as well as an acoustic analogy within an annular duct provides the best results compared to measurements. Moreover a Large-Eddy Simulation (LES) is performed on the axial compressor. The turbulent rotor wakes interaction with the downstream stator vanes is correctly resolved and creates broadband acoustic sources. The LES allows a better understanding of physical phenomena in order to improve analytical models. Finally the application of the numerical method provides the acoustic power spectra radiated within the duct and appears to be promising.;Keywords: Aeroacoustics, unsteady aerodynamic simulation, rotor-stator interaction, fan noise, tonal noise, broadband noise.