A note on turbulent spots over a rough bed in wave boundary layers

This study is a continuation of the investigation of turbulent spots in wave boundary layers over a smooth wall reported by Carstensen et al. [J. Fluid Mech. 646, 169–206 (2010)10.1017/S0022112009992825]. The present paper summarises the results of an experimental investigation of turbulent spots in wave boundary layers over a rough wall. Two kinds of experiments were made: flow visualization tests and velocity profile measurements. The experiments show that turbulent spots as observed in the smooth-wall wave boundary layers are present irrespective of wall roughness conditions. As in the smooth-wall case the turbulent spots over the rough wall appear locally in time and space and grow in size as time progresses.