A Method for Deriving Tone Noise Information from CFD Calculations on the Aeroengine Fan Stage

Abstract

A wave splitting procedure is proposed by which noise information can be derived from CFD calculations on the aeroengine fan stage. Noise propagation in the ducted regions is compared with well-understood linear behavior in parallel wall ducts. Deviations from this behavior are used to highlight important features of the flow solution. These include genuine flow features such as non-linear acoustic interaction as well as dissipation and boundary condition errors deriving from the numerical solution of the equations. Properly applied, the method provides quantitative noise source amplitudes, accounting for (modest) reflections from the boundaries of the CFD domain. At the same time confidence can be gained that the CFD results are accurate for the wavelengths and frequencies being analyzed, and that the CFD domain sufficiently covers the region of interest. Examples are given of how the method can be applied to steady and unsteady CFD calculations. Limitations of the method are also discussed.