KY EPSCoR: Investigation of Wall Shear Stress Modifications Occurring due toTurbulent Flow 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 conducting high quality experiments in a novel flow facility capable of reproducing the combined effects of surface roughness flow injection which would be experienced by the turbulent boundary layer forming over a large ablative thermal protection system undergoing pyrolysis. The approach used in this study will be to conduct detailed investigations of the modifications made to the turbulent flow over both geometrically simple surface roughness and a complex surface which replicates an actual ablative thermal protection system. Determination of the wall shear stress will require the modification of an existing turbulent channel flow facility to produce fully developed flow conditions over these surfaces. Detailed turbulence measurements on the flow over the surfaces will then be conducted while measuring pressure losses to skin friction while simultaneously injecting air flow through the surface to replicate the exhaust of pyrolysis gas during ablation. The results will then be used to develop scaling parameters which can be used to develop accurate boundary conditions which can in turn be applied for flow simulations of ablative surfaces during re-entry and to develop empirical laws for modeling 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, a fundamental problem with practical applications for re-entry aerodynamics.