Journal of Fluid Mechanics


Turbulent boundary layer under a solitary wave


a1 Department of Civil, Environmental and Architectural Engineering - University of Genoa, Via Montallegro 1, 16145 Genova, Italy


The boundary layer generated by the propagation of a solitary wave is investigated by means of direct numerical simulations of continuity and Navier–Stokes equations. The obtained results show that, for small wave amplitudes, the flow regime is laminar. Turbulence appears when the wave amplitude becomes larger than a critical value which depends on the ratio between the boundary-layer thickness and the water depth. Moreover, turbulence is generated only during the decelerating phase, or conversely, turbulence is present only behind the wave crest. Even though the horizontal velocity component far from the bed always moves in the direction of wave propagation, the fluid particle velocity near the bottom reverses direction as the irrotational velocity decelerates. The strength and length of time of flow reversal are affected by turbulence appearance. Also the bed shear stress feels the effects of turbulence presence.

(Received June 03 2008)

(Revised July 31 2008)