Heatshield Ablation Pattern Roughness Onset and Effects

This project will develop a practical method for predicting pattern roughness onset and quantitative effects on heat and mass transfer rates for heatshield materials such as Phenolic Impregnated Carbon Ablator (PICA) and environments such as those anticipated for the Crew Exploration Vehicle (CEV). Surface roughness patterns (e.g., scallops, crosshatching) form on many materials ablating under turbulent flow conditions. Equivalent sand grain roughness models are inaccurate and inappropriate for calculating Stanton numbers. In Phase I, we will develop a near-term method based on pattern roughness data, observations, and models from diverse fields. This method may predict Stanton number increases directly from material and aerothermal environment information instead of sequentially predicting pattern dimensions, equivalent roughness height, and Stanton number effects. We will also plan a more rigorous longer-term model and validation tests to be implemented in Phase II.