Effect of Chevrons on Double Stream Jet Noise from Hybrid CAA Computations

Double stream nozzle configurations are computed to evaluate the noise radiated to the far field. The method combines a LES simulation with an acoustic solver based on surface integral method. The presented works have been carried out in the framework of the EXEJET French national program and focus on the effects of chevrons which are added to an axisymmetric reference configuration. The LES computations rely on hybrid meshes, which mix structured and unstructured grids, combining tetrahedra, pyramids and hexahedra. This approach has been developed in the past years at Onera. The computations are performed on both the axisymmetric and the chevron configurations. The LES results are used as inputs to a Ffowcs Williams and Hawkings acoustic surface integral method to reconstruct the far field noise. Several hybrid grids are considered and the grid effects are analyzed. In particular, the appearance of a vortex shedding phenomenon is observed for one of the grids family and is found to depend on the ability of the grid to resolve the nacelle external boundary layer. The computations are run in advance of the test campaigns to be carried out at the Onera Cepra19 facility. Comparisons with experimental measurement will be performed as they become available in the course of the EXEJET project.