Adjoint-informed ignition characterization

Abstract eng:
The adjoint of the linearized reactive compressible flow equations is used to quantify ignition sensitivity in unsteady combustion. The corresponding sensitivity gradients are used to map the boundary between successful and failed ignition. Owing to the ultimately binary outcome (i.e., it succeeds or fails after some period), care must be taken to define an appropriate cost functional that both quantifies ignition success and varies smoothly near its threshold. Such a cost functional is designed to measure early-time behavior, and an indicator function identifies successful ignition. The approach is demonstrated in a homogenous reactor and a non-premixed shear layer. The line-search algorithm is shown to automatically detect the ignition boundary from an initial set of modeling parameters within a few iterations. The gradient information is used to construct a tangent space for mapping the ignition boundary subject to specific constraints.

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