Compliance of combustion models for turbulent reacting flow simulations

The utilization of low-dimensional manifold combustion models for large-eddy simulation (LES) of turbulent reactive flows introduces model simplifications that represent sources of uncertainties in addition to those arising from turbulent closure models and numerical discretization. The ability to quantitatively assess these uncertainties in the absence of measurements or reference results is vital for reliable and predictive simulations of practical combustion devices. This paper is concerned with the extension of the manifold drift term to LES to examine the compliance of a particular combustion model in describing a quantity of interest (QoI) with respect to the underlying flow-field representation. This drift term was previously introduced as a key component of the Pareto-efficient combustion (PEC) framework. The behavior of the drift term is examined in a series of test cases. To this end, large-eddy simulations of a partially-premixed turbulent pilot flame with inhomogeneous inlet streams are performed, in which the non-premixed flamelet/progress-variable (FPV) model and the premixed filtered tabulated chemistry LES (F-TACLES) formulation are employed. The drift term is shown to be capable of identifying chemically sensitive regions with respect to user-specific QoIs. With this, a species-specific combustion regime indicator is derived by computing the relative magnitude of the drift terms for different combustion models. Comparisons with commonly employed flame indicators suggests that the flame index and other indicators that are solely based on major species and flame topology are insufficient in describing complex physical processes in multi-regime combustion.