Experimental and Numerical Study of Pyrolysis Gas Pressure in Ablating Test Piece

The pyrolysis gas pressure and temperature inside ablator pieces are measured in an arc-heated wind tunnel. The obtained pressure and temperature data are compared with the computed results that account for unsteady ablation. In the calculation, the motion of pyrolysis gas is determined by solving the mass and momentum conservation equations assuming a finite permeability determined in our previous study. Though a quantitative agreement is not yet reached, the observed trend in pressure showing an initial increase, a decrease, and eventually reaching a plateau is reproduced qualitatively by the present calculation. It is suggested from the experimental data and the computed result that delamination of the ablator likely occurs at the region where the ablator is not fully charred but partially pyrolyzed, which results in a smaller porosity and higher pyrolysis gas pressure in the region.