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(searched for: doi:10.2514/8.7469)
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Jiayang Xu, Cheng Huang, Karthik Duraisamy
AIAA Journal, Volume 58, pp 618-632; https://doi.org/10.2514/1.j057959

Abstract:
A multifidelity framework is established and demonstrated for the prediction of combustion instabilities in rocket engines. The main idea is to adapt appropriate fidelity modeling approaches for different components in a rocket engine to ensure accurate and efficient predictions. Specifically, the proposed framework integrates projection-based reduced-order models (ROMs) that are developed using bases generated on truncated domain simulations. The ROM training is performed on truncated domains, and thus does not require full-order model solutions on the full rocket geometry, thus demonstrating the potential to greatly reduce training costs. Geometry-specific training is replaced by the response generated by perturbing the characteristics at the boundary of the truncated domain. This training method is shown to enhance the predictive capabilities and robustness of the resulting ROMs, including at conditions outside the training range. Numerical tests are conducted on a quasi-one-dimensional model of a single-element rocket combustor, and the present framework is compared to traditional ROM development approaches.
Cheng Huang, William E. Anderson, Charles L. Merkle, Venkateswaran Sankaran
AIAA Journal, Volume 57, pp 2055-2068; https://doi.org/10.2514/1.j057061

Abstract:
A multifidelity framework oriented toward efficient modeling of combustion dynamics that integrates a reduced-order model (ROM) for the combustion response into the Euler equations is proposed. The ROM is developed from computational fluid dynamics (CFD) simulations of a combusting flow that is periodically forced at the boundaries of a reduced domain. Galerkin’s method is used to reduce the high-order partial differential equations to a low-order ordinary differential equation system via proper orthogonal decomposition eigenbases generated from a reduced-domain dataset. Evaluations of the framework are performed based on parametric studies of a simplified test problem for a model combustor showing distinguishable combustion instability behavior. Two-way information transfer between the ROM and Euler solutions is accomplished by interface matching at the boundaries of the reduced domain. It is shown that accurate predictions require the use of multiple ROMs to account for both upstream- and downstream-traveling perturbations. Characteristic boundary conditions are required at both reduced-domain boundaries to minimize wave reflections and preclude generic unstable responses in the multifidelity model predictions. Comparisons with CFD solutions show the multifidelity model is capable of capturing overall instability trends.
Kevin Miller, James Sisco, Nicholas Nugent, William Anderson
Journal of Propulsion and Power, Volume 23, pp 1102-1112; https://doi.org/10.2514/1.26826

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