Modélisation bas ordre des instabilités de combustion haute-fréquence dans les moteurs fusées à propulsion liquide

Combustion instabilities in liquid rocket engines are difficult to predict and model. The EM2C laboratory, in partnership with CNES and ArianeGroup, is therefore developing StaHF, a low-order code based on the modal projection of the pressure oscillations, to estimate the growth rate of instabilities. Phenomena such as combustion response are modeled via source terms. The low-order approach is interesting because it requires reduced numerical resources and is thus well suited to the pre-sizing stages. This thesis comprises three main parts: first, a presentation of the low-order tool, with the models already present and the additions made to the code. Next, we present the main mechanisms identified as damping acoustic oscillations, such as losses via the nozzle, viscous losses, the effect of nonlinear acoustics, and the interaction of acoustics with turbulence. The final section applies StaHF to reproduce the results of two test benches, the NPCC and the BKD. This work extends the prediction capabilities of the StaHF code, which was not equipped in damping terms. Also, the ability to use FTF and FDF was added, making it possible to model the response of H2 flow modulation in injection lines. Application to the NPCC has shown that the nonlinear behavior of the acoustic wave appears to be the leading cause of damping and the appearance of the limit cycle. Modeling the BKD enables us to create an application case using the full range of damping models, as well as several flame response, pressure response, velocity response and H2 flow modulation. Interesting orders of magnitude of growth and damping rates have been obtained.