Multi-Component Reduced-Order Model Framework for Rocket Engines*

Combustion dynamics is characterized by the coupling between heat release, hydrodynamics and acoustics. In combustion engines, this complex coupling can lead to combustion instabilities that can cause devastating engine failures. Even with advances in modern computational capabilities, high-fidelity (e.g., Large Eddy) simulations of full-scale combustors remain out of reach. In this work, we develop a multi-component Reduced Order Model (ROM) framework to enable efficient prediction of combustion dynamics in rocket engines. Projection-based model reduction methods, leveraging the least-squares Petrov Galerkin methods, are adapted to obtain efficient and accurate ROMs to represent complex combustion dynamics near rocket injector elements. These ROMs are effectively built on small-domain (e.g., 2-3 elements)  compared to the full-scale engine (> 100 elements) using offline LES simulations with excitation of essential dynamics at the training stage. Computational fluid dynamic (CFD) models are used in regions in which the dominant features are acoustically propagating waves (manifolds, injector posts and nozzle) and coupled to the aforementioned network of ROMs which represent the near-injector regions. The framework is demonstrated to predict combustion instability characteristics in a laboratory multi-element rocket combustor.