In-Situ Adaptive Manifolds for modeling a turbulent piloted jet flame with inhomogeneous inlets

Manifold-based combustion models reduce the computational cost of turbulent combustion simulations by projecting the thermochemical state onto a lower-dimensional manifold and solving the resulting manifold equations separately from the flow solver. In-Situ Adaptive Manifolds (ISAM) is an approach that computes solutions to manifold equations 'on-the-fly' and stores the solutions using In-Situ Adaptive Tabulation (ISAT). It has demonstrated computational and memory cost savings for combustion processes featuring two inlet streams over the traditional method of precomputing and pretabulating manifold equation solutions. In this work, ISAM is extended to more complex combustion phenomena featuring more than two inlet streams and is tested on a turbulent piloted jet flame featuring an inhomogeneously mixed central stream of fuel and oxidizer that burns with an air coflow. Special care is required in deploying the ISAT algorithm with ISAM for more complex models. ISAT performs significantly better when Jacobians are computed with manifold solutions with respect to a grid in normalized equivalence ratio rather than a grid in mixture fraction due to the shift in the stoichiometric mixture fraction from inhomogeneous mixing of fuel and air in the central stream.