AEM Department Head Search Seminar: Tom Schwartzentruber, University of Minnesota

Gas-Surface Interactions for Hypersonics and Near-Space

Materials used for hypersonic vehicles and low-orbiting satellites must withstand harsh environments. Hypersonic flight generates a shock-heated, partially dissociated gas. Reactive atomic oxygen and nitrogen drive chemical reactions on material surfaces resulting in ablation or complex oxide layer formation. In low earth orbit, the outer region of Earth’s atmosphere is comprised mainly of oxygen atoms. Satellite materials must withstand collisions with reactive oxygen atoms at orbital velocity (7-8 km/s). For near-space altitudes, the flow transitions from continuum to free-molecular and gas-surface scattering dominates lift and drag.

This presentation describes new gas-surface interaction models that can be used in rarefied or continuum flow solvers to simulate low orbit satellites and hypersonic vehicles. The models were developed using recent molecular beam experimental data. The first type of model uses molecular beam scattering data for mixtures of dissociated air species reacting with high temperature carbon materials. This data is used to construct a 20-reaction air-carbon ablation model for use in large-scale CFD simulations of hypersonic flows. The second type of model is based on beam-surface scattering data for orbital velocity oxygen atoms impacting various satellite materials, including near-specular scattering materials that have the potential for low drag and high lift/drag. Instead of relying on conventional assumptions of either fully diffuse or specular reflection, this new model will provide quantitative predictions of satellite aerodynamics in low earth orbit.