Radiative flamelet generated manifolds for solid fuel flame spread in microgravity

Recently, U-shape flammability maps have been constructed showing minimal oxygen concentration vs. flame strain for opposed flame spread in microgravity. 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 two-dimensional (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, newly developed coupled radiative flamelet generated manifolds (CR-FGM's) are created using a simplified one-dimensional (1D) 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. Differences between the 2D model data and the CR-FGM's are then identified to be from flame-wall interactions and curved flame structure effects. These differences are addressed using an a-priori error analysis conducted for various intermediate species comparing detailed 2D simulations with the CR-FGM. Results show the CR-FGM's are capable in predicting the wide range of chemical states for most of the flow regions.