**Numerical Study of the Hydrodynamics of Waves and Currents and Their E**ff**ects in Pier Scouring**

**Matias Quezada 1,\*, Aldo Tamburrino 1,2 and Yarko Niño 1,2,\***


Received: 31 August 2019; Accepted: 22 October 2019; Published: 28 October 2019

**Abstract:** The scour around cylindrical piles due to codirectional and opposite waves and currents is studied with Reynolds Averaged Navier–Stokes (RANS) equations via REEF3D numeric modeling. First, a calibration process was made through a comparison with the experimental data available in the literature. Subsequently, not only the hydrodynamics, but also the expected scour for a set of scenarios, which were defined by the relative velocity of the current (*UCW*), were studied numerically. The results obtained show that the hydrodynamics around the pile for codirectional or opposite waves and currents not have significant differences when analyzed in terms of their velocities, vorticities and mean shear stresses, since the currents proved to be more relevant compared to the net flow. The equilibrium scour, estimated by the extrapolation of the numerical data with the equation by Sheppard, enabled us to estimate values close to those described in the literature. From this extrapolation, it was verified that the dimensionless scour would be less when the waves and currents are from opposite directions. The *UCW* parameter is an indicator used to adequately measure the interactions between the currents and waves under conditions of codirectional flow. Nevertheless, it is recommended to modify this parameter for currents and waves in opposite directions, and an equation is proposed for this case.

**Keywords:** horseshoe vortex; pile scour; waves and currents; computational fluid dynamics; REEF3D
