Ultra-high bypass ratio (UHBR) engines are designed as compact as possible and are characterized by a short asymmetric air inlet and heterogeneous outlet guide vanes (OGVs). The flow close to the fan is therefore circumferentially nonuniform (or distorted) and the resulting noise might be impacted. This is studied here at take-off conditions by means of a simulation of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations of a full-annulus fan stage. The model includes an asymmetric air inlet, a fan, heterogeneous OGVs, and homogeneous inlet guide vanes (IGVs). Direct acoustic predictions are given for both inlet and aft noises. A novel hydrodynamic/acoustic splitting method based on a modal decomposition is developed and is applied for the aft noise analysis. The noise mechanisms that are generally considered (i.e., interaction of fan-blade wakes with OGVs and fan self-noise) are shown to be impacted by the distortion. In addition, new sources caused by the interaction between the stationary distortion and the fan blades appear and contribute to the inlet noise.

New ultra high bypass ratio architectures may significantly affect the fan tonal noise of future aircraft engines. Indeed, such a noise source is supposed to be dominated by the interaction of fan-blade wakes with outlet guide vanes. However, shorter nacelles in these engines are expected to trigger an important air-inlet distortion that can be responsible for new acoustic sources on the fan blades. Full annulus simulations based on the unsteady Reynolds-averaged Navier-Stokes equations are presently used to study this effect. Simulation results show that the air-inlet distortion has a main effect in the fan-tip region, leading to a strong variation of the fan-blade unsteady loading. It also significantly modifies the shape of the fan-blade wakes and, consequently, the unsteady loading of the outlet guide vanes. Acoustic predictions based on the extension of Goldstein's analogy to an annular duct in a uniform axial flow are presented and show that the fan sources notably contribute to the fan tonal noise. The air-inlet distortion is responsible for an increase of the noise radiated by both the fan and the outlet guide vane sources, leading to a global noise penalty of up to three decibels.

This paper presents an acoustic evaluation, based on computational fluid dynamics (CFD) simulations, of the Airbus Nautilius engine integration concept applied to the Onera NOVA airplane. This innovative concept is characterized by the integration of two ultra high bypass ratio (UHBR) engines into the fuselage rear end so as to maximize the boundary layer ingestion (BLI). This concept is evaluated against a reference configuration with conventional podded engines. The study is made at take-off conditions representative of the sideline acoustic certification point and is limited to fan tonal noise which is expected to be the most affected contribution to aircraft noise by the BLI. The numerical methodology is based on two steps. First, steady simulations of the whole aircraft with body force modeling for the fan are performed in order to provide the flow characteristics at the inlet and outlet of the engine ducts. Then, unsteady simulations of the engines restricted to the in-duct domain are conducted using the preceding flow characteristics. All numerical simulations are performed with Onera's CFD solver elsA. Steady and unsteady aerodynamic results are evaluated with a focus on the main noise generation mechnisms. Acoustic power estimates are also provided by applying Goldtsein's analogy with the unsteady loadings on fan blades and stator vanes as source terms.