Acoustic Scattering Behaviour of an Aero Engine Injector: Numerical Investigation Using Compressible CFD and CAA

During development of modern lean burn aero engine combustors, prediction and characterization of injector thermoacoustic response plays an important role. The SCARLET (SCaled Acoustic Rig for Low Emission Technologies) test rig fulfills this need by providing acoustically defined upstream and downstream conditions under realistic operating conditions to characterize the acoustic response of full-scale injectors in a single sector setup. This work presents results from the complementary numerical analysis campaign that aims to reproduce the acoustic scattering behaviour as measured in the SCARLET rig. As a first step, non-reacting flow simulations were performed using fully compressible CFD simulations and the CAA (computational aero acoustics) method to compute upstream and downstream acoustic fields. The results obtained are then post-processed based on a multi-microphone method to yield the acoustic scattering matrix, which follows the employed experimental post-processing strategy. Results obtained from both methods show satisfactory agreement with measurements. Geometrical simplifications and their implications on scattering behaviour are investigated to achieve a trade-off between accuracy and geometrical complexity. Both methods are compared in terms of their inherent advantages and disadvantages. Limitations associated with employed models and possible improvements are discussed.