Waves plus currents crossing at a right angle: near-bed velocity statistics

ABSTRACT

Wave–current flow over a bottom covered with different roughness elements was analysed to provide new insights into the statistical properties of the near-bed velocity. Experimental data of three different experimental campaigns, with orthogonal waves and currents over a sandy bed, a gravel bed and a rippled bed were used. Velocity profiles were acquired by means of a micro-ADV. The paper focuses on the effects that the waves have on the statistics of the velocity in the current direction. In particular, in the case of a steady current only, the near-bed velocities closely follow a Gaussian distribution. When waves are added, the distribution becomes double-peaked. In order to get single-peaked velocity distributions the total velocity events in the current direction were split in two classes according to the sign of the wave directed velocities. The nature of the distribution functions is influenced by the mass conservation principle and, in the rippled bed case, by the vorticity dynamics.

Keywords:

• Bed roughness
• higher-order statistics
• probability distribution function
• ripples
• wave boundary layer
• wave–current interaction

ORCID

C. Faraci http://orcid.org/0000-0003-1532-4190

R.E. Musumeci http://orcid.org/0000-0002-1022-0571

Additional information

Funding

This work has been funded by Italian Ministry of University, Education and Research, PRIN 2012 Project “Hydro-morphodynamics modelling of coastal processes for engineering purposes”, and by the EC project Hydralab+ [contract no. 654110].