Gas/Surface Interaction Study of Low-Density Ablators in Sub- and Supersonic Plasmas

Ablation experiments have been carried out with the carbon-phenolic material AQ61
and a non-pyrolyzing carbon fiber preform in sub- and supersonic air and nitrogen plasmas
in the VKI Plasmatron facility. We performed an in-situ recession analysis, including vol-
umetric ablation, and observed the temperature and radiance of the surface for emissivity
estimations, as well as spatial molecular radiation profiles in the boundary layer, which
were compared to a numerical approach. Surface temperatures as low as 1600 K allowed
observation of the temperature distribution over the surface using an infrared camera. The
carbon preform test samples were varied in shape as well as regarding their fiber direction.
Sublimation of the surface was reached in supersonic plasma flow at a cold wall heat flux
of 9.5 MW/m 2 . Carbon preform emissivities were found to be in the order of 0.86 - 0.97.
A stagnation line description with an ablation boundary condition helped to reproduce
experimentally measured boundary layer emission profiles of the CN violet molecule. In
spite of the very simplified model, emission intensities were in the same order of magni-
tude compared to the experimental data. The model was able to reconstruct the location
of the maximum emission for two cases. The char layer was examined by Scanning Electron
Microscopy, illustrating degradation after nitrogen ablation.

ISBN:978-1-62410-281-3

Publication year:2014

Keywords:ablation