Abstract

Rough-wall turbulence can be considered the norm rather than the exception, because surfaces rarely remain perfectly smooth over longer periods of time. Historically, investigations of rough-wall turbulence have focussed on the fluid dynamics aspects, with the wall roughness itself receiving little attention. More recently, the topographies of rough walls and their effects on near-wall turbulence have received increased interest. Surface skewness and effective slope have been identified as key topographical parameters. In this talk, I will discuss and classify topographical parameters that influence the fluid dynamical roughness effect. Using results from recent direct numerical simulations I will show that we need to consider parameters beyond surface skewness and effective slope to fully capture roughness effects.