Disturbances Generated by Random and Periodic Surface Roughness: Experiments and Models

Experiments and simulations that consider how three-dimensional surface roughness affects laminar-to-turbulent transition have a history of mixed success. Two-dimensional roughness has been well understood as a generator of Tollmien‐Schlichting waves. Three-dimensional roughness has been less well understood but is now the subject of increased attention associated with the development of transient growth theory. Experiments that address the receptivity and growth of transient disturbances generated by roughness arrays and models of these processes are reviewed here. Additionally, an extension to random, distributed roughness that takes advantage of manufactured surfaces is described and implemented. The approach lends itself to rigorous comparisons between experimental and simulation data and theoretical models.