Turbulent Flow Field and Scour Characteristics around Bridge Pier in Combined Wave and Current Conditions

Abstract

This experimental study investigates the effect of surface waves that are superimposed on a unidirectional current around a bridge pier in a gravel bed, which employs particle image velocimetry (PIV). A comprehensive examination of various flow characteristics, which include the intermittency factor (IF), turbulent kinetic energy (TKE), and vorticity analysis, is conducted to elucidate the variations around the pier with respect to the Keulegan–Carpenter (KC) number. The findings reveal a correlation between the KC number and the flow dynamics in combined conditions: specifically, due to combined wave–flow conditions, escalation in the frequency of vortices near the pier and the increment in turbulent strength, in terms of the TKE. Of note, this augmentation in turbulent strength is associated with an increase in the KC number. At a low KC number, the maximum scour depth occurred downstream near the pier, which shifted to upstream with an increase in the KC number. In addition, the results could be utilized for the development and validation of numerical models, which accurately estimate the local scour under combined flow conditions.