GALCIT Colloquium

The Curie-Prigogine Principle states that quantities whose tensorial characters differ by an odd number of ranks cannot interact in an isotropic medium. For example, chemical affinity (a scalar quantity) cannot cause a directed heat or diffusion flux in an isotropic system. Such processes can however become coupled at system boundaries, at which the medium becomes anisotropic. At high temperatures, such as those experienced during atmospheric entry, enhanced chemical reactions at the surface of a vehicle lead directly to strong non-continuum behavior, driven by large concentration gradients and diffusion fluxes, in the hot gas surrounding the spacecraft. This phenomenon, referred to as continuum breakdown, requires the development of high-fidelity computational models that can provide accurate predictions of surface heating and fluid/structure interactions during atmospheric entry. Our group has established a new set of parameters based on Generalized Chapman-Enskog Theory for rapid identification of continuum breakdown in reacting flows, as part of a larger effort to construct state-of-the-art hybrid computational tools for combined continuum/rarefied reacting flows. I will demonstrate how the Generalized Chapman-Enskog Theory and the Curie-Prigogine Principle together establish an important connection among gas-phase chemical reactions, surface chemical reactions, and diffusion-driven continuum breakdown relevant for modern hypersonic flight vehicles and ablative thermal protection systems. Sensitivity of the extent and location of continuum breakdown with respect to the surface chemistry model is investigated, and the development of a carbon oxidation model for carbon-based ablators is presented.