Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7051822 | Experimental Thermal and Fluid Science | 2018 | 19 Pages |
Abstract
Spallation is a phenomenon in which solid particles are ejected off the surface of an ablative material in a high-enthalpy, high-shear flow field. The main contributor to this phenomenon in carbon-based heat shields is the mechanical erosion of carbon fibers weakened by oxidation decomposition. The dynamics of this phenomenon, which are poorly characterized in the literature, strongly affect the ablation rate of the material. In state-of-the-art codes, ablation by spallation is modeled using a “failure” ablation rate that is empirically determined. The present study aims at understanding the rate of ablation of low-density carbon materials. Results from a test campaign at the NASA Langley Hypersonic Materials Environmental Test System (HYMETS) arc jet facility are used to examine spallation. High-speed multi-camera imagery at 44,000â¯fps is used to generate velocity vectors of spalled particles emitted from carbon-fiber samples exposed to an arc jet airflow. The imagery recorded approximately 4Ã106 unique particles, indicating that spallation is a potentially non-trivial process. The velocities of the particles ejected from the surface were found to be between 10â¯m/s and 20â¯m/s, accelerating to velocities as high as 250â¯m/s further away from the sample surface. Although the particle diameters were not directly observable, estimates suggest anywhere from 0.06% to 5.6% of the mass loss from the sample occurred due to spallation.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
Sean C.C. Bailey, Dominik Bauer, Francesco Panerai, Scott C. Splinter, Paul M. Danehy, J. Matthew Hardy, Alexandre Martin,