Low-order modeling of combustion instability applied to cryogenic propellants

Combustion instability is a major threat to be dealt with during the design and development phase of new liquid rocket engines. If unpredicted, its onset easily yields to thermal or mechanical failure of the engine and of the mission as well. The present work focuses on the low-order modeling of combustion instability. In particular, a recently introduced response function formulation is reported and applied. Its novelty lies in the indirect link between acoustics and unsteady heat release, which passes through the modeling of the shear coaxial injector dynamics. Such injector is assumed to be capable of cyclically accumulating and releasing propellant vortexes where the mixing takes place. Such model is then applied to two different test-cases, namely one fed by gaseous propellant, i.e. the CVRC test-case, while the other by supercritical fluids, namely the BKD test-case. Results show how the CVRC instability features are well reproduced, while several model improvements are needed for the BKD