Comparison of numerical methods and combustion models for LES of a ramjet configuration

Ramjets are very sensitive to instabilities and their numerical predictions can only be addressed adequately by Large Eddy Simulation (LES). With this technique, solvers can be implicit or explicit and handle structured, unstructured or hybrid meshes... Turbulence and combustion models are other sources of differences. In the present work, the impact of these options is investigated for the ONERA ramjet burner. To do so, two LES codes developped by ONERA and CERFACS compute one operating condition which is found experimentally to be stable. The computational domain is the same for both codes and encompasses all three nozzles: two at the air inlets, one at the exit and the fuel alimentation box. Both meshing strategies aim at locally refining the grid to enforce high resolution where combustion occurs. Preliminary LES results of the two codes underline the overall robustness of LES. Mean flow features at the various critical sections are reasonably well predicted by both codes. Disagreement mainly appear in the chamber where combustion positions differ pointing to the importance of the combustion and subgrid mixing models. For the operating point simulated, the two LES produce different energy containing motions. With CEDRE, a low frequency dominates while AVBP produces different ranges of low frequencies that can be linked with acoustic modes of the configuration.