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The OpenFOAM ® toolbox is used to establish two numerical models for the gas-phase phenomena observed during composite solid propellant combustion. The models were identified to evaluate and compare the performance of the pressure-and density-based approaches typically used to simulate the gas-phase phenomena. The pressure-based model is based on the rhoReactingFoam combustion model included in the OpenFOAM ® libraries. The density-based model is based on a vorticity-velocity formulation. Both models include detailed kinetic mechanisms and species transport. The combustion capabilities of the pressure-base model are validated against a known case for piloted methane (CH 4 )/air jet flames. Preliminary validation test results show satisfactory agreement between model predictions and literature data. The model development as well as future work planned is discussed. Nomenclature= effective thermal flux = constant pressure specific heat of the mixture = constant pressure specific heat of the k th species = diffusion coefficient ̅ = acceleration due to gravity = specific enthalpy of the k th species = heat of formation of the k th species at temperature (298.15 K) = sensible enthalpy = pressure = change in energy density due to radiation ̅ = velocity vector ̅ = diffusion velocity vector of the k th species ̿ = identity tensor ̅ = diffusion flux ̅ = diffusive flux vector of the k th species = kinetic energy 1 PhD Student, Department of Process Engineering, eonretief@sun.ac.za, AIAA Member 2 = species flux = number of gas-phase species present in a mixture or chemical kinetic mechanism = place-holder variable = mixture concentration ̅ = heat flux density = universal gas constant = temperature = reference temperature ̅ = average molecular weight of the species = molecular weight of the k th species = mass fraction of the k th species = thermal conductivity = dynamic viscosity = density ̿ = viscous stress tensor ̿ = summation of the viscous and turbulent stress tensors ̅ = vorticity vector ̇ = net molar production rate of the k th species ̇ = enthalpy of formation of the k th specie at temperature (298.15 K) = gradient of a quantity = divergence of a quantity = curl of a quantity

The OpenFOAM ® toolbox has been used to develop a pressure-based, as well as a density-based gas-phase numerical model for the combustion of ammonium perchlorate (AP) and hydroxyl-terminated-polybutadiene (HTPB) composite solid propellants. Onedimensional (1D) correlations as well as a fully-coupled multi-region multi-physics model are evaluated for the condensed phase to provide the inlet conditions for the gas-phase models. Compared to the fully-coupled approach, the 1D correlations offer the prospect of reduced computational resource requirements, at the expense of neglecting two-dimensional (2D) effects in the condensed phase. A detailed AP/HTPB kinetics mechanism comprised of 37 species and 127 reaction steps is investigated to provide the required kinetic information. The solution algorithm of coupling the condensed-and gas-phase models for both 1D and fully-coupled approaches are discussed. Nomenclature= effective thermal flux = constant pressure specific heat of the mixture = constant pressure specific heat of the k th species = AP pyrolysis activation energy = binder pyrolysis activation energy ̅ = acceleration due to gravity = specific enthalpy of the k th species = heat of formation of the k th species at temperature (298.15 K) = sensible enthalpy = pressure ̇ = heat flux = change in energy density due to radiation ̅ = velocity vector ̅ = diffusion velocity vector of the k th species ̿ = identity tensor ̅ = diffusive flux vector of the k th species = kinetic energy = species flux = number of gas-phase species present in a mixture or chemical kinetic mechanism = place-holder variable = surface regression rate , = universal gas constant 1 PhD Student, Department of Process Engineering, eonretief@sun.ac.za, AIAA Member 2 = temperature = reference temperature ̅ = average molecular weight of the species = molecular weight of the k th species = mass fraction of the k th species = thermal conductivity = dynamic viscosity = density ̿ = viscous stress tensor ̿ = summation of the viscous and turbulent stress tensors ̅ = vorticity vector ̇ = net molar production rate of the k th species ̇ = enthalpy of formation of the k th specie at temperature (298.15 K) = ammonium perchlorate = binder = condensed phase = surface = gradient of a quantity = divergence of a quantity = curl of a quantity