Augmentor Stability

ABSTRACT: As with all other combustion devices, the augmentors in high-performance gas turbine engines are at risk of combustion instability. While it is tempting to apply brute force CFD to address this problem, at best high fidelity CFD may reveal what happens but not why it happens. While thousands of high fidelity CFD runs could be used to generate empirical type trends, that path is impractical. Instead, it is imperative to understand the sources and root causes of instability if this serious technical issue is to be overcome. Doing so will dramatically reduce development risk and cost, while also allowing maximum performance. To achieve this insight into combustion instability, GTL has developed the Universal Combustion Device Stability (UCDS) process. UCDS is a physics-based model that employs a hybrid analytical-computational analysis wherein energy transport in and out of unsteady fields can be tracked. Doing so quantifies the sources of unsteady energy and their effect on the overall stability. A sophisticated set of computational tools are in place to facilitate this approach. Altogether, UCDS can predict instability, quantify sources of driving or damping, and provide a critical understanding of combustion instability in augmentors at a significantly reduced computational cost. BENEFIT: Combustion instability, whether it is in the form of low frequency rumble or high frequency screech is a serious risk (likelihood and severity) to propulsion system development programs. This instability is characterized by organized pressure oscillations that can severely damage engine hardware or structural damage limiting augmentor operability. To overcome this issue, developers have largely used a cut-and-try approach, which has proven to be costly and not always reliable. In contrast, the UCDS process provides clear insight into why the propulsion system behaves the way it does. This allows developers to design the issue out of their system early or quickly mitigate the issue if it arises during testing. This approach will greatly reduce development cost, schedule and risk, while also allowing performance to be improved. Since UCDS is built from a general formulation it can be applied to practically any combustion device, including augmentors, combustors, liquid rockets, solid rockets, ramjets and scramjets.