Advanced finite-volume numerics and source term assumptions for G-Equation modelling of propane/air flames
2022-01-0471
03/29/2022
- Event
- Content
- G-Equation models represent propagating flame fronts with an implicit two-dimensional surface representation (level-set). Level-set methods are fast, as transport source terms for the implicit surface can be solved with finite-volume operators on the finite-volume domain, without having to build the actual surface. However, they carry out several approximations and assumptions whose practical impact on the accuracy of combustion simulations is often not properly understood. In this study, we analyzed all source terms making up the FRESCO CFD code’s G-Equation solver for simulating propane/air flames. We employed three well-established constant-volume configurations: a one-dimensional, freely-propagating laminar flame; a disc-shaped, constant-volume swirl combustor; and torch-jet flame development through an orifice from a two-chamber device. We tested the explicit (sub-cycled) vs. implicit formulation for the standard transport operators (advection, diffusion, compressibility). For the swept-volume chemistry and species source term, we assessed available formulations from the literature, and developed a more accurate estimator for the burnt/unburnt split cell composition. Then, we developed a signed-distance-function based method which provides a more stable reinitialization of the level-set field at every time-step. We found that simplifying assumptions common to several G-Equation implementations, for straightforward terms such as compressibility and advection, lead to large errors predicting the propagation of even laminar flames, with deviations up to ~300% in simulated vs. formulated flame speed. Other enhanced numerics, like SDF field reinitialization and the improved chemistry source term, instead strongly affect the stability of the simulations, leading to smoother flame propagation and significantly larger solver time-steps.
- Citation
- Perini, F., Dal Forno Chuahy, F., Sircar, A., Splitter, D. et al., "Advanced finite-volume numerics and source term assumptions for G-Equation modelling of propane/air flames," SAE Technical Paper 2022-01-0471, 2022, .