Tone Noise Predictions of a Full-Scale UHBR Engine at Approach Condition with Inflow Distortion Effects

摘要

Modern UHBR (Ultra High Bypass Ratio) aeroengines are characterized by reduced fan speeds and very short asymmetric intakes, so that the mean flow entering into the nacelle is no more uniform along the azimuthal direction (particularly at operating conditions with non-zero angle of attack). Such short inlets and inflow distortions can highly modify the dominant tone noise contributions known from conventional turbofans. This paper presents aeroacoustic investigations applied to a full scale UHBR engine in the framework of the CleanSky2 European project, ASPIRE. Numerical simulations based on (u)RANS calculations are coupled to integral formulations derived from the Ffowcs-Williams and Hawkings analogy and to CAA (Computational AeroAcoustics) based on non-linear disturbance Euler equations, in order to assess the source generation and sound propagation of the fan-OGV stage with and without inflow distortion. Simulations are performed at approach operating condition and CAA is focused on the intake region and forward radiation. It is shown that the inflow distortion effects significantly modify the harmonic loads (on rotor and stator) and so the associated circumferential mode spectrum. Although the blade passing frequency remains cut-off, these effects give rise to an increase of overall power level in the forward direction, and a non expected reduction in the bypass duct too.