Numerical investigation of laminar-turbulent transition for hypersonic blunt bodies with distributed roughness*

Transitional and turbulent heating play a crucial role in the design and analysis of hypersonic vehicles. Distributed roughness alters the mean flow, e.g., generating locally separated wake regions depending on the roughness amplitude, which may enhance and/or introduce new boundary layer instability mechanisms. Previous numerical and experimental work have focused on flat plates and (blunt) cones, with recent experiments also exploring the effect of roughness on boundary layer transition in blunt body flows. However, there has been limited computational studies for boundary layer transition over hypersonic blunt bodies with roughness. In this work, we use direct numerical simulation (DNS) to study the effect of distributed surface roughness on the boundary layer laminar-to-turbulent transition process for a cylinder in hypersonic flow. We apply adaptive mesh refinement to achieve the necessary grid resolution required to capture transition to turbulence over stagnating blunt bodies at a tractable computational cost. We also investigate the impact of roughness amplitude and phasing on transition and compare results between two Navier-Stokes solvers, US3D and CHAMPS.