Improved Heat Release Models for Augmentors

Combustion stability is critical to the operational performance and safety of military jet engines. Dynamic instability results from positive feedback coupling that can occur between heat release (combustion) and pressure oscillations (acoustics) in the augmentor. Dynamic instabilities are poorly understood and present designers with a particularly challenging problem when they arise. It is not currently possible to simulate dynamic instability with highly-resolved computational fluid dynamics (CFD). For this reason, reduced-order models are typically used to study dynamic instability. A key component of these models is the heat release model. Most existing heat release models are based on flame-sheet models that predict the mean location of the flame. The heat release model is derived by perturbing the flame with small-amplitude velocity perturbations. Many of the assumptions used to reduce existing models are unsatisfactory for augmentors. In augmentors, heat release is distributed, and vorticity (i.e., large-scale perturbations of the flame) can play a key role in determining stability. We will develop improved heat release models that are tailored specifically for augmentor flows. These models will lead to an improved understanding of augmentor flame dynamics and will also be used to develop models for predicting dynamic instability for augmentor conditions.