We present novel observations from direct numerical simulations of transitional Mach 8 flow over a 15° compression ramp ablator. Heating streaks over the ramp are seen to undergo a half-wavelength shift near the location of transition from laminar to turbulent boundary layer flow. This phenomenon leads to an intriguing pattern of ablation grooves on the surface. Our analysis shows that the underlying mechanism is driven by the baroclinic torque in the strongly stratified near-wall region. We discuss the impact of this baroclinic shift for a surface undergoing ablative recession and assess its sensitivity to different thermal boundary conditions and perturbation amplitudes.

Direct numerical simulations (DNS) are performed over a 15° compression ramp undergoing ablation at Mach 8 to examine fluid-ablation interactions (FAI) on transitional high-speed boundary layers. The experiments at these conditions with a rigid wall are first numerically replicated for a laminar flow. Heating streaks are introduced by introducing perturbations in the baseflow informed by prior stability calculations. The ramp is then replaced by a low-temperature ablator in our DNS and the interaction of the streaks with the recessing ablator surface are examined. Different approaches from two independently developed solvers are used to study this problem. Overall, both solvers provide qualitatively and quantitatively very similar results; however, differences in streak amplification and mass blowing magnitudes are observed. We discuss the difficulties in accurately predicting ablation and present the first findings regarding its influence on the perturbation evolution and transition to turbulence for this configuration.

The efficacy of immersed boundary (IB) methods with adaptive mesh refinement (AMR) techniques is assessed in the context of atmospheric entry applications, including effects of chemical nonequilibrium (CNE) and gas–surface interactions (GSI). We scrutinize a conservative cut-cell IB method and two non-conservative IB methods, comparing their results with analytical solutions, data from the literature, and results obtained with a reference solver that operates on body-fitted grids. All solvers employ the same external thermochemistry library, ensuring that all observed differences can be attributed solely to differences in the underlying numerical methodologies. We present results for eight benchmark cases. Four verification cases verify the implementation of chemistry, transport properties, catalytic boundary conditions, and shock capturing. Four validation cases encompass blunt geometries with adiabatic and isothermal, as well as inert, catalytic and ablative boundary conditions. Overall, the results obtained with the IB solvers are in very good agreement with the reference data. Discrepancies arise in cases with large temperature or concentration gradients at the wall, and these are linked to conservation errors inherent to ghost-cell and interpolation-based IB methods. Only a strictly conservative cut-cell IB method is on par with body-fitted grid methods.