Finite-Element, Adaptive, Grid Solver to Predict Thermochemical Ablation in Composites

Huntsville Sciences Corporation (HSC) proposes to develop a new and innovative approach for predicting the pore pressures and structural behavior of a thermochemically decomposing composite ablator material like those commonly used to insulate rocket nozzles. The proposed method uses a two-dimensional (2-D) finite element solver with adaptive grid features in solving a modified form of the energy and mass continuity equations proposed by Weiler[1] which describe the thermochemical ablation process. The adaptive grid features of the proposed method will permit the accurate resolution of the large pressure gradients that exist at the pyrolysis zone / virgin material interface which currently pose resolution problems with other finite element and finite difference techniques. The proposed method is 2-D. It accounts for the spatial variation in material properties ,i.e. thermal capacitance, thermal conductivity, and porosity in computing the temperatures and pore pressures in the ablating material. The Phase I code will accurately track the surface recession and the char and pyrolysis zone formations that occur during the ablation process. The planned Phase II enhancements include (a) modifications to the Phase I code to solve the complete energy and mass continuity governing equations, (b) the addition of chemical kinetics, (c) the addition of a two-phase water vapor/condensation model, and (d) developing efficient interfaces to codes like ACE [4] and MEIT [5] which produce the surface input data for this model . With the Phase II code enhancements, this code will be used to accurately predict ply separation in thermochemically decomposing rocket nozzle liners which is a problem of prime interest to NASA.