A Strain-Consistent Epsilon-Based Flamelet Model for Non-Premixed Turbulent Combustion

Speaker: Sylvain L. Walsh, University of California, Irvine
September 24, 2026

Presentation

Abstract

Flamelet models are widely used in turbulent combustion simulations, representing chemical reaction in complex flows as an ensemble of quasi-laminar flame structures subjected to local strain. Detailed chemical kinetics can thereby be incorporated through precomputed flamelet libraries without solving the full finite-rate chemistry problem during the flow simulation, while retaining a model for unresolved turbulence–chemistry interaction. A central challenge, however, is establishing a physically consistent coupling between the computed turbulent flow and the strain-dependent state represented by the flamelet library.

This talk examines a strain-rate inconsistency in the conventional flamelet/progress-variable (FPV) formulation for non-premixed combustion and proposes an alternative coupling based on the turbulent kinetic energy dissipation rate, ε. Two-dimensional RANS simulations of a transonic accelerating reacting mixing layer are performed using one-step finite-rate chemistry, a conventional FPV model, and the proposed ε-based flamelet model. The results support ε as a physically motivated coupling variable for strain-rate-controlled non-premixed flamelet modeling without requiring a scalar-dissipation-rate closure, while explicit transport of selected species enables composition to be preserved across locally extinguished regions without relying on a transported progress variable.

Biography

Sylvain Walsh is a Ph.D. Candidate at the University of California, Irvine, under the co-advisement of Prof. William A. Sirignano and Prof. Feng Liu. His research focuses on LES and RANS combustion modeling, with particular interest in flamelet models. During the summer of 2026 he was an OSTEM intern with the Computational Aerosciences Branch at NASA Ames Research Center, working with Dr. Nguyen Ly on integration and verification of reaction-flow capabilities within the Launch, Ascent, and Vehicle Aerodynamics (LAVA) Framework.

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