ON THE IMPACT OF CORE FLOW INLET-GUIDE-VANES ON THE TONAL NOISE SIGNATURE OF A TURBOFAN ENGINE

Fan noise is one of the major aircraft noise sources at most operating conditions, featuring broadband and tonal contents. Tone noise is typically caused by the periodic interaction between the fan wakes and the outlet-guide-vanes (OGV). Additionally, a fraction of the wakes enter the primary flow. These impinge on the inlet-guide-vanes (IGV), leading as well to sound generation. Nevertheless, this noise mechanism is usually neglected due to the smaller size of the IGV compared to the OGV. This study numerically assesses the contribution of the IGV to the tone noise footprint on the ACAT1 test vehicle, a modern scaled-down fan, experimentally analysed in 2018 within the TurboNoiseBB project. The noise prediction methodology consists of the use of an extensively validated uRANS solver, chained to an acoustic post-processing to extract the acoustics. A vast number of simulations have been performed, at different operating points, and working lines, to provide a complete assessment of this phenomenon. For each operating condition, three configurations have been simulated: the complete assembly with the fan rotor, OGV and IGV, a configuration without IGV and a configuration without OGV. The noise footprints of those three computations have been compared to derive the contribution of the IGV. Surprisingly, the IGV lead to high noise levels and result in the dominant source of noise at most operating conditions, in the for- ward and rearward arcs. The strong hub secondary flows and an in-phase impact of the wakes on the IGV seem to be responsible for such an efficient noise radiation. These results cannot be compared with experimental data because the blade count of the OGV and the IGV of this test vehicle is the same, making it not possible to isolate the contribution of both components. Nonetheless, this work signals a potential risk of parasitic tone noise levels that could arise in current and future engines. There is a need for further research on this topic to confirm whether these conclusions are generalisable or not to real engines.