Surrogates for combustion instabilities in annular combustors
Résumé
While the computational power is still increasing, thus arousing the
interest for high-fidelity simulations, the need of low-order models is also felt
to both predict and understand combustion instabilities at low costs. Historically
applied to simple systems like longitudinal Rijke tubes to unveil the driven mechanisms
leading to instability, they have recently been adapted to more complex
configurations such as annular combustors. A network model is presented here to
predict thermo-acoustic modes in an annular combustion chamber fed by burners
connected to an annular plenum, typical of modern combustor designs. Explicit
expressions of the growth rate are derived in several cases showing key parameters
controlling the stability. In more general situations, no explicit solution can
be obtained. Nevertheless, such an analytical model can be solved numerically at
low-cost compared with 3D acoustic tools and high-fidelity simulations. In this
framework, efficient sensitivity techniques and UQ methods can be developed to
tackle the UQ problem: “How can we assess the risk of instability in industrial
combustors at the predesign stage?”.