Engine-Level Simulation of Liquid Rocket Combustion Instabilities Transcritical Combustion Simulations in Single Injector Configurations

Detailed understanding of turbulent combustion in liquid rocket engines (LRE) requires an ability to predict the coupling between the transient features, acoustics, vortex/shear layer dynamics and the unsteady combustion heat release. Conventional and ad hoc models that mimic or match one set of conditions but fail in another test case cannot be used for reliable predictions. This paper presents a simulation strategy based on Large-Eddy Simulation (LES) that uses a finite-volume scheme on multi-block, structured grids and solves the full multi-species, compressible LES equations using a hybrid central-upwind scheme to capture both turbulence shear flow and large density gradients. The sensitivity of predictions to the real gas equation of state such as the Peng-Robinson one is addressed in this study. The main modeling challenges concern the simultaneous capture of the flame structure, the flame-turbulence interactions and the regions of compressibility. The current work focuses on turbulent combustion in three single injector configurations for these objectives: (a) trans-critical liquid oxygen (LOX) / gaseous hydrogen (GH2) combustion, (b) trans-critical LOX/methane combustion and (c) high-pressure GOX/methane combustion with thermo-acoustic instabilities. Results will be reported on the flame structure, liquid core length and spreading rate, and comparison with data where appropriate. Finally, for LES of such problems, a more fundamental challenge is to determine the implication of the LES subgrid closures for real gas flame dynamics. As a preliminary effort, the Linear-Eddy sub-grid model (LEM) is being applied to some of these cases.