Common vortical structure of turbulent flows over smooth and rough boundaries

Abstract

The bursting phenomenon is a common feature of turbulent boundary layers irrespective of the wall roughness condition. Consistent with Theodorsen's conjecture, recent direct numerical simulation studies have shown that the dynamics of this bursting process over smooth walls is directly linked to the presence of powerful vortical structures with a general horseshoe-type configuration. We describe the results of physical experiments that demonstrate that these vortex structures are also present in turbulent boundary layers over rough walls. They appear to form the central element in a recurring, highly nonlinear cycle of turbulence and burst generating instability