  The article investigates liquid oxygen (LOx)-methane supercritical combustion
dynamics in a multi-element rocket scale combustor using large eddy simulation
(LES). A complex framework of real gas thermodynamics and flamelet generated
manifold (FGM) combustion model is invoked to simulate transcritical oxygen
injection and supercritical methane combustion. A benchmark Mascotte chamber,
Rocket Combustion Modelling (RCM) Test Case, i.e. RCM-3 (V04)/G2 test case, is
used to validate the real gas FGM model in the LES framework. The validation
study accurately reproduces experimental flame structure and OH concentration,
demonstrating the FGM model's importance in incorporating finite rate kinetics
in LOx-methane combustion. Subsequently, the numerical framework investigates a
specially designed multi-element combustion chamber featuring seven
bidirectional swirl coaxial injectors. The analyses capture the complex
hydrodynamics and combustion dynamics associated with multiple swirl injectors
operating at supercritical pressure, effectively demonstrating the initiation
of transverse acoustic waves and examining the effect of local sound speed on
the evolution of acoustic modes in the combustor. The dominant frequency modes
shed light on understanding the role of injectors in enhanced combustor
dynamics. Spectral analysis reveals the interplay of the upstream injector and
chamber acoustics due to possible frequency coupling. The results also
highlight the effect of fuel injection temperature on the stability of the
combustor, revealing a violent dynamic activity for lower fuel injection
temperature associated with the longitudinal acoustic mode of the combustor.
The investigation appropriately reproduces self-sustained limit cycle
oscillations at lower fuel injection temperatures and corroborates the
conventional understanding of combustor instability.
