LES of High-Frequency Combustion Instability in a Single Element Rocket Combustor

Abstract

In the present work, results of numerical simulations to capture the high-frequency combustion instability in a two-dimensional combustor with hydrogen (H2) / oxygen (O2) injector are shown. Three sets of computations, in which the locations to install the injector element are varied with an aim to change the degree of coupling between heat release fluctuation and pressure oscillation, are conducted. In the first computation (named as RUN1), the injector is installed at the center of combustion chamber. In the second and third computations (named as RUN2 and RUN3), the injector is installed at the off-centered location of combustion chamber. In RUN3, the flow forcing is attempted by adding an energy source term in the energy conservation equation to generate the first transverse mode (1T) in the combustion chamber. Although the amplitudes of pressure oscillations in the first two computations are relatively small, the result of RUN2 shows that pressure oscillation at 4kHz, which corresponds to the 1T mode of combustion chamber, is significantly excited. In RUN3, the 1T mode of combustion chamber is successfully generated by the flow forcing. After switching off the flow forcing, however, the amplitude of pressure oscillation decays rapidly and self-sustained oscillation can not be established. The results of three cases are analized by using the balance equation for acoustic energy. The analysis indicates that the Rayleigh term works as a driving mechanism for instabilities, but the other damping term has a large negative value and prevents the glowth of pressure oscillations for all three cases. Finally, the present work is extended to three-dimensional LES and the preliminary result is shown.