Modeling effective Lewis numbers in non-premixed flames: insights from DNS data of Sandia flame B

摘要

Flamelet-based chemistry tabulation is a popular technique for the simulation of turbulent non-premixed flames. In this approach, the one-dimensional flamelet equations are solved, and relevant thermo-chemical properties are tabulated with respect to the mixture fraction and either its scalar dissipation rate or a progress variable. When solving the flamelet equations, the choice of the Lewis numbers plays an important role. Mean scalar species profiles in turbulent diffusion flames can be represented by one dimensional flamelets with an adequate choice of the Lewis numbers. These effective Lewis numbers are found to transition from their laminar values to unity, depending on the local mixing conditions. Modeling this transition is important, as adequately capturing differential diffusion effects can have a large impact on processes that present a significant sensitivity on scalar transport (e.g., soot nucleation from polycyclic aromatic hydrocarbons). In this work, effective Lewis numbers are extracted from Direct Numerical Simulation data of Sandia flame B (Re_(jet) ≈ 8200) using a recently developed technique based on a flamelet-based error map analysis. The results are then compared against a experimental data.