Experimental analysis of turbulence and local erosion in a squares-section bridge pier in channel with a 90 degree derivation

Abstract

An adequate analysis of scour, transport, and sedimentation of particles allows for the mitigation of erosion effects on structures built over a watercourse, as is the case with bridges. The present research utilized a 90-degree bifurcation channel, constructed at a laboratory scale, measuring 0.60 m in width and depth, with a main channel length of 6 m and a secondary channel length of 2.2 m. At the center of the channel bifurcation, a square-section pile measuring 0.10 m on each side and 0.90 m in height was installed. The sediment depth in the channel is 0.20 m, resting on 0.10 m of gravel. An Acoustic Doppler Velocimeter (ADV) was employed to determine instantaneous velocities. The pile significantly increased the scour upstream of the structure, resulting in a maximum scour of -0.182 m. Additionally, it was observed that the instantaneous velocity in the flow direction  reached maximum values of 0.30 m/s, close to the mean flow velocity (0.33 m/s), indicating how the pile altered the flow pattern, creating zones of high turbulence. Turbulent velocities, specifically near the channel bed, peaked at 0.10 m/s in . Downstream, the Reynolds stresses  near the pile were maximal, ranging from 0.02 to 0.04 (m/s)² at a height of z = 0.08 m, then decreasing to values below 0.015 (m/s)² for z = 0.11 m, indicating that the presence of the pile generates an increase in sediment transport and contributes to intense erosional processes in its vicinity. Near the channel bed (z = 0.08 m), the Kolmogorov length scales were reduced to values between 0.1 and 0.3 mm, reflecting the presence of turbulent structures with limited size and high intensity.