Multifidelity UQ strategies for laser-ignited rocket combustors

In a rocket combustor, hydrodynamic ejection of a laser-induced plasma placed in a co-flowing fuel-oxidizer jet can facilitate re-ignition capability throughout a mission. The present work aims at understanding the various scenarios in which successful ignition may occur and builds probability distributions of ignition success and associated post-ignition pressure rise in the rocket chamber. In uncertainty space, this is a high-dimensional problem, and run-to-run variabilities arise from uncertainty in the deposited laser characteristics, and the stochastic nature of underlying turbulent mixing of propellants. A reduced order low-fidelity surrogate model is constructed that achieves a compression ratio of two orders of magnitude compared to the accurate high-fidelity simulations. This is accomplished by using a simplified chemistry mechanism and reduction in the simulation scale-resolution. Further, the surrogate model is constructed by means of an inverse problem in which deterministic processes from high-fidelity pilot cases are used to estimate the parameters in the low-fidelity space that map to high-fidelity counterparts. Thereafter, multi-fidelity Monte Carlo sampling is employed to obtain realizations of the uncertainty space. Finally, we present analysis of ignition likelihood and sensitivities.