Surrogates for Combustion Instabilities in Annular Combustors

Abstract

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?".