What is it about?
In the present study, we analyze the broadband noise of an ultra high by-pass ratio fan/OGV stage developed at Ecole Centrale de Lyon. Wall-modeled large eddy simulations (LES) of a periodic fan/OGV sector are performed at approach conditions on an unstructured grid that is well refined for direct noise propagation. Comparisons between wall-resolved and wall-modeled computations are performed using a 2.5D simplified configuration of the fan/OGV stage, and show a good agreement. This justifies the use of wall-modeled simulations for the full-span configuration. A good agreement is found between LES and RANS aerodynamic results. However, some differences can be found in the tip gap region and near the hub, where large coherent structures appear. Additionally, a small recirculation bubble can be observed from approximately 60% of the fan blade span in the LES. In this study, the broadband noise is directly computed from the fully-compressible LES solver and compared with predictions from available analytical models. The input data for the analytical models, such as mean and turbulent flow statistics, are obtained from the LES computation. A good agreement is found for the predicted sound power levels between direct LES noise predictions and the LES-informed analytical models. This confirms the capability of the LES numerical setup to directly predict far-field noise. However, some discrepancies can be observed at low frequencies. These might be attributed to the additional noise sources that are present in the LES, which are not considered by the analytical models.
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Why is it important?
Unlike previous studies in the literature that use acoustic analogies or analytical models, which introduce a certain number of assumptions, the far-field noise is directly resolved from the LES, and compared to advanced analytical models, for which the input data are extracted from the LES. The direct noise computation from the LES requires a specific mesh refinement and numerical setup.
Perspectives
In the future a 360° full stage configuration will be considered using LES. Indeed, the precise number of blades and the geometry of the stage strongly influence rotor-stator interaction noise and actual LES methods suffer from the fact that cut-on propagating modes defined by the Tyler and Soffrin rules only apply for a full 360° configuration.
Jean Al Am
Ecole Centrale de Lyon
Read the Original
This page is a summary of: Direct noise predictions of fan broadband noise using LES and analytical models, June 2022, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2022-2882.
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