Investigation of Surface Roughness Effects on Turbulence over an Ablative Thermal Protection System

The objective of the proposed research is to generate experimental data that will improve modeling capabilities of the turbulent flow over ablative thermal protection surfaces. This work will be achieved by teaming high quality experiments with precisely matched simulated flow conditions. The approach used in this study will be to: (1) Characterize an ablative surface in varying stages of pyrolysis using 3D profilometry measurements to digitize the surface; (2) reproduce the surface structure at each stage of pyrolysis at a scale appropriate for wind tunnel usage; (3) place the scaled surfaces into specialized a turbulent channel flow facility, and conduct detailed turbulence measurements on the flow over the surfaces while simultaneously injecting air through them to replicate the exhaust of pyrolysis gas during ablation; and (4) perform matched flow simulations using the open source software FreeCFD. The software will be modified by introduction of a novel subgrid-scale turbulence model, and comparison between the experiments and simulations used to develop empirical laws to model the subgrid fluxes produced by the rough surface and flow injection. The expected outcome of this research activity is a deeper understanding of the combined effects of roughness and blowing on a turbulent wall-bounded flow as well as revealing the strengths and weaknesses of the turbulent models which could be used for simulating the flow over ablating thermal protection systems during re-entry.