On the Development of Coupled Radiative Flamelet Generated Manifolds to Predict Solid Fuel Flame Spread in Microgravity

Recently, U-shape flammability maps have been constructed showing minimal oxygen vs. flame strain for opposed flame spread in micro-gravity. Due to the absence of buoyancy in microgravity, flammability experiments require a microgravity environment and are costly to perform. Alternatively, detailed numerical simulations can be conducted to explore the flammability maps if sufficiently detailed chemistry mechanisms and radiation models are available. The purpose of this study is to develop such an approach and to explore the viability of using flamelet modeling descriptions. For this effort, a detailed 2D flame spread model is developed that includes multi-step complex chemistry and fully coupled radiation heat transfer. The model is validated against measurements using the NASA BASS data and is shown to predict reasonable flame spread rates over a range of far-field oxygen levels. Next, flamelet generated manifolds (FGM) are created using a simplified one-dimensional descriptions that include a quasi-coupled, fuel boundary that is shown to be critically important for capturing the spatially dependent variation of mixture fraction on fuel surfaces. An a priori error analysis is conducted of intermediate species comparing detailed 2D simulations with FGM. Results show promising agreement for most of the flow regions except near the flame attachment location where some differences are observed due to flame wall interactions before the fuel starts to burn.