Abstract
ABSTRACT A computational study of the nonlinear rocket-engine combustion instability is presented for an engine with 30 coaxial methane-oxygen injector ports, a choked nozzle, and a combustion chamber. Three combustion chamber lengths of 18 cm, 24 cm, and 30 cm are simulated with differing instability modes depending on length. Computations using a three-dimensional unsteady k − ω shear-stress transport delayed detached-eddy simulation method provide detailed time-resolved information about the combustion instability. Our flame-index analysis explains why the premixed-flame structures dominate over diffusion flame-structures in the driving mechanism for the instability. This causes the engine to become more unstable as the mixture becomes more fuel rich. Spontaneous longitudinal-mode and tangential-mode instabilities are observed. The oscillation amplitude of the two instability modes vary in alternating fashion during the simulation time. The alternating behavior of the two instability modes can be modified by pulsing the injector mass-flux on the mixture ratio at a particular frequency.
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