Seminar: Unsteady spallation of low-density carbon fiber ablators - Apr. 17
Francesco Panerai
Assistant Professor, Aerospace Engineering
University of Illinois at Urbana-Champaign
Friday, Apr. 17 | 10:40 A.M. | AERO 114
Abstract: We discuss recent findings from inductively coupled plasma wind tunnel experiments on the spallation of lightweight charring ablators. Spallation effects due to flow shear stresses and internal pressure build-up have been the subject of renewed interest by the ablation community. A direct comparison of PICA and FiberForm ablation under supersonic air and nitrogen plasma revealed distinct processes attributed to the presence of oxidation reactions, or absence thereof. Spallation in nitrogen plasma is characterized by intermittent particle release events, attributed to carbonaceous deposits that accumulate at the ablator surface. These precipitates originate from carbon sublimation and nitridation products that subsequently redeposit on the layered ablator surface, decreasing surface permeability. Particle release events occur as a result of the consequent increase in interior pressure caused by continued sublimation and production of pyrolysis gases beneath the carbonaceous deposition.Ìý
These effects result in dominant contributions to the overall ablation processes, where unsteady spallation can account for upwards of 45% of the total mass loss in nitrogen plasma, with immediate implications to heat shield design. By contrast, no comparable carbon depositions or unsteady particle releases are observed in air plasma at similar enthalpies, suggesting that, while sublimation and nitridation processes are active, all gaseous carbon is consumed by atomic oxygen near the surface. Overall, our results provide new insights on the high-temperature ablation regime, where the tight interactions of sublimation, carbon deposition, and boundary layer carbon/oxygen reactions require further investigation.
Bio: Francesco Panerai is an Assistant Professor in Aerospace Engineering at the University of Illinois at Urbana-Champaign. His research covers advanced materials for extreme environments, transport in porous media, and hypersonic aerothermodynamics. Prior to Illinois, he was a research scientist at NASA Ames Research Center. He received his PhD and Research Master in Aeronautics and Aerospace from von Karman Institute for Fluid Dynamics in (Belgium) and a M.Sc. and a B.Sc. in Mechanical Engineering from the University of Perugia (Italy). He is recipient of the 2019 Air Force Young Investigator Award and is an AIAA Associate Fellow. He is one of the founding members of the Center for Hypersonics and Entry Systems Studies (CHESS) at the University of Illinois.