Role of Transient Growth in Roughness-Induced Transition

Surface roughness can have a profound effect on boundary-layer transition. However, the mechanisms responsible for transition with three-dimensional distributed roughness have been elusive. Various Tollmien-Schlichting-based mechanisms have been investigated in the past but have been shown not to be applicable. More recently, the applicability of transient growth theory to roughness-induced transition has been studied. A model for roughness-induced transition is developed that makes use of computational results based on the spatial transient growth theory pioneered by the present authors. For nosetip transition, the resulting transition relations reproduce the trends of the Reda and passive nosetip technology (PANT) data and account for the separate roles of roughness and surface temperature level on the transition behavior.