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Numerical analysis of ablation process on a two dimensional external surface

Aykan, Fatma Serap
The thermal response analysis of an ablative material on a two dimensional external surface is performed. The method is applied to both rectangular and cylindrical coordinate systems, where rectangular coordinate system is used for comparison with results available in literature. The current study solves the decomposition of the material at high temperatures by using the nth order Arrhenius equation but excludes the removal of char from the surface due to mechanical erosion or phase change and considers that the ablation process takes place in a finite zone. The method considers the whole domain as one computational domain, eliminating the necessity to check the positions of the start and end of decomposition zone. The decomposition of pyrolysis gases and/or char that may occur at high temperatures and the chemical reaction between pyrolysis gases and char is neglected while pyrolysis gases are assumed to behave as ideal gas. The pressure is taken as a constant value on a whole physical domain. The formulation for one-dimensional case is validated by experimental results obtained from literature. The two-dimensional case in a Cartesian geometry is formulated and an algebraic transformation is used to normalize the region in both directions and transformed at same time into a square computational domain in order to get a solution for the variable thickness domains. The formulation for two-dimensional case is revised for the cylindrical coordinates with finite length in the axial direction. To solve geometries where the outer surface deviates from cylindrical, the formulation is scaled and transformed into a non-dimensional square computational domain. The method is also applied to a two layer material problem in axisymmetric geometry. In all problems, the radiation and constant heat flux boundary conditions exist on the outer surface while whole domain is initially at