Numerical analysis of fan noise for the NOVA boundary-layer ingestion configuration

Aim of this paper is to investigate the effects of the turbulent flow developing over a fuselage on fan noise for BLI embedded propulsion systems. Such configurations can suffer from inlet flow distortions and ingestion of turbulence at the fan plane with consequent impact on both broadband and tonal fan noise. The analysis is performed on a modified version of the Low-Noise NASA SDT fan-stage integrated into the ONERA NOVA fuselage in order to reproduce the NOVA BLI configuration. The numerical flow solution is obtained by solving the explicit, transient and compressible lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOW®. The acoustic far-field is computed by using the Ffowcs-Williams & Hawkings integral solution applied to a permeable surface. All simulations are performed for an operating condition representative of a take-off with power cut-back. Installation effects due to the BLI configuration are quantified by comparison with an isolated configuration of the modified Low-Noise SDT fan-stage at the same operating condition. It is found that the BLI fan-stage, which is not optimal, is characterized by strong azimuthal fan blade loading unsteadiness, less axisymmetric and coherent rotor wake tangential velocity variations and higher levels of in-plane velocity fluctuations compared to the isolated engine. This resulted in no distinct tonal components and higher broadband levels in the far-field noise spectra, as well as in an increment of cumulative noise levels up to 18 EPNdB. This study, which represents the first high-fidelity CFD/CAA simulation of a full-scale aircraft geometry comprehensive of a BLI fan/OGV, provides with a clear understanding of the change of the noise sources in BLI integrated configurations