Comparative analysis of flow velocity distributions around square and circular bridge piers using ADV and CFD

Bridge piers integrated into open channels induce substantial modifications in flow dynamics, necessitating a detailed analysis of hydraulic performance and structural safety. In this context, the effects of critical parameters such as the geometry, size, and placement of bridge piers on flow velocities are vital to maintaining structural integrity and environmental balance. This study investigates the streamwise velocity distributions upstream of eight bridge pier configurations, comprising square and circular geometries arranged in single-axis and double-axis layouts under a constant net flow width, through a combined experimental and numerical approach. The experimental velocity fields were obtained using an Acoustic Doppler Velocimeter (ADV) in a laboratory flume. At the same time, the numerical solution was performed using the Computational Fluid Dynamics (CFD)-based ANSYS-Fluent software, employing the Realizable k-ε turbulence model. A total of 32 simulations were performed, covering four discharge conditions under subcritical flow. Computed and measured velocities were compared at 7.5 cm, 15 cm, and 22.5 cm upstream of the piers, at an elevation of 6.5 cm above the channel bed. The mean absolute relative error over all configurations was 10.58%, ranging from 6.80% for six square piers in a double-axis arrangement to 12.47% for three circular piers in a double-axis arrangement. Square geometries yielded a lower overall deviation (10.04%) than circular ones (11.13%), which is attributed to the fixed separation point imposed by the sharp-edged geometry and to its more accurate representation by the Cartesian mesh. The numerical model systematically overestimated the measured velocities yet consistently reproduced the transverse velocity distribution and its streamwise development across all configurations.