Exhaust Noise Reduction of Realistic 3D Lined Turbofans Submitted to Strong Shear Layers

Abstract

Actran/DGM is a Discontinuous Galerkin Method (DGM) software that solves the Linearized Euler Equations (LEE) in time domain. The spatial order of the method is adaptative and ranges from 1 to 16, offering great meshing freedom to the user. In its axisymmetric version, this software has been validated against experiments and cross-verified using other software packages through the CEE-funded TURNEX project, see for example Tester and compared with a Finite Element Method(FEM) commercial software : Actran/TM using a very specific technique described in Manera. Although working in the frequency domain is much preferable for moderated problem sizes, the time domain approach has obvious advantages for very large problems (beyond kr ≡ 50 in 3D): it is highly scalable for parallel computations and the RAM consumption is quite low for big aeroacoustic models and. However, some typical frequency-based concept, such as the admittance boundary conditions or the non-reflecting boundary conditions, have to be translated in the time domain. Furthermore the well known Kelvin-Helmholtz instabilities are observed: as shown in Manera, keeping them in the solution is essential, but special care must be taken to keep a good stability of the numerical scheme. Through the cases presented in this paper, all those characteristics are highlighted. This paper focuses on the numerical prediction of the sound propagation at the exhaust of 3D realistic engines. More precisely, it aims at showing the ability of Actran/DGM to solve very large exhaust problems, especially with liners, and in presence of complex sheared flow.