_:n70b33ae1c47e4e77833f00a776cfc666xb0
<http://schema.org/description>
"Combustion instabilities are a major concern in the design of Liquid Rocket\nEngines (LREs) and gas turbines. During this PhD work, several directions were\nexplored to understand and mitigate their effects. First, more efficient and\nrobust numerical methods for their prediction in complex combustors were\ndesigned. In this matter, a novel type of modal expansion, named a frame\nexpansion and comparable to the classical Galerkin expansion, was introduced to\nbuild more accurate acoustic Low-Order Models (LOMs), able to account for the\nfull geometrical complexity of industrial combustors. In particular, the frame\nexpansion is able to accurately represent the acoustic velocity field near\nnon-rigid-wall boundaries, a crucial ability that the Galerkin method lacks. An\nentire class of novel numerical methods, based on the frame expansion, were\nthen designed and combined with the state-space formalism to build acoustic\nnetworks of complex systems. The second ingredient in the prediction of\nthermoacoustic instabilities is the flame dynamics modeling. This work dealt\nwith this problem, in the specific case of a cryogenic coaxial jet-flame\ncharacteristic of a LRE. Flame dynamics driving phenomena were identified\nthanks to three-dimensional Large Eddy Simulations (LES) of the Mascotte\nexperimental test rig where both reactants (CH4 and O2) are injected in\ntranscritical conditions. Several LES with harmonic modulation of the fuel\ninflow at various frequencies and amplitudes were performed in order to\nevaluate the flame response to acoustic oscillations and compute a Flame\nTransfer Function (FTF). The stabilization of this flame in the near-injector\nregion, which is of primary importance on the overall flame dynamics, was also\ninvestigated thanks to multi-physics two-dimensional Direct Numerical\nSimulations (DNS), where a conjugate heat transfer problem is resolved at the\ninjector lip."
<https://deepai.org/publication/low-order-modeling-and-high-fidelity-simulations-for-the-prediction-of-combustion-instabilities-in-liquid-rocket-engines-and-gas-turbines>