Turbulence Over Chains of Hemispherical Ribs Under Waves in a Current

This is the authors' abstract. We don't add key points for this paper.

A series of flume experiments was conducted to investigate how unidirectional surface waves interact with a rough boundary. The roughness consisted of several arrays of ribs with varied pitch‐to‐height ratios ( L / d = 2, 4, and 8; L = pitch distance and d = rib height). The mean flow and its key turbulence parameters associated with the contributions of burst‐sweep cycles of the Reynolds shear stress were analyzed to examine the interaction of combined wave‐current flow over ribs. The inner scaling of the mean velocity over the rib roughness resulted in a downward shift of the log‐law region. The probability distributions of the velocity fluctuations exhibited a unimodal form in the presence or absence of surface waves in the ambient flow. The streamwise spectral and cospectral energy distributions differed due to the rib spacing and superimposed surface wave. This study also reports the dominant turbulent bursting events (i.e., ejections and sweeps) that contribute to the total Reynolds shear stress for current flow‐ and wave‐induced cases. The effect of the chain of ribs on higher‐order moments subject to wave‐current interactions is also explored, because momentum transport is sensitive to symmetry breaking and intermittency.