Although accurate prediction of combustion instability in full scale rocket combustors using high fidelity simulations is beyond current capability, validated simulations on the scale of single- or few-element combustors have been obtained. To take advantage of the data from simulations of limited domains, a model that uses spatially distributed flame transfer functions (FTF) obtained from high-fìdelity simulations along with non-linear Euler equations is investigated. In this paper, the proposed reduced fidelity model and the extraction of flame transfer functions are explored. A model rocket combustor that presented a self-excited combustion instability with pressure oscillations on the order of 10°7c of mean pressure is used for demonstration. It is shown that the model can reproduce the unsteady behavior of the single element combustor that was measured in experiment and predicted by a high fidelity simulation reasonably well. The effects of control parameters such as the number of modes included in the FTF, number of sampling points used in the Fourier transform of unsteady heat release calculation, and mesh size are studied. The reduced fidelity model could reproduce the limit cycle amplitude very closely, with deviations within 2% of the mean pressure when the same mesh as in the high fidelity simulation was used with a multi-mode FTF that contained unsteady heat release information at frequencies at least one mode higher than the main frequencies of interest. In addition to matching the limit cycle amplitudes, the reduced fidelity model reproduced accurate mode shapes and provided linear growth rates that reasonably matched those observed in the experiment.
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