This study investigated the distribution and dynamics of the Turbulent Kinetic Energy (TKE) around a group of three tandem piers using a combination of numerical simulations and experimental measurements. The Volume of Fluid (VOF) method, coupled with the k-$\epsilon$ turbulence model, was implemented in ANSYS FLUENT to replicate the free-surface flow conditions. An experimental validation was conducted using Acoustic Doppler Velocimetry (ADV) to assess the model’s capability at capturing the turbulence characteristics. While the model effectively reproduced the near-bed turbulence, it consistently underestimated the TKE magnitudes across the flow domain, particularly in regions of strong vortex-induced turbulence. Discrepancies emerged in the confined regions between the piers, where the velocity profiles were overestimated at the surface and underestimated near the bed and mid-depth, impacting the TKE predictions. Despite these inconsistencies, the general pattern of the TKE distribution aligned with the experimental trends, though the absolute values remained underestimated due to the inherent limitations of the k-$\epsilon$ model. The model’s performance in less turbulent regions demonstrated improved accuracy, reinforcing its applicability for moderate turbulence simulations. To further examine the interaction between vortex structures and the TKE, velocity distributions were analyzed at three specific depths (z/h = 0.15, 0.4, and 0.62). The findings showed the critical role of vortex shedding in TKE generation and dissipation, with notable variations in the turbulence intensity influenced by structural confinement effects. This study offers a novel, high-resolution evaluation of the k-ε model’s ability to predict TKE distributions around tandem piers, using spatially detailed comparisons with the experimental data. Unlike previous studies that broadly acknowledged the model’s limitations, this work systematically identifies the specific regions, particularly vortex-dominated zones, where its predictive accuracy significantly degrades.

Understanding the three-dimensional flow turbulence generated by the combined presence of a bridge abutment and adjacent piers is essential for accurately predicting local scour, a primary cause of hydraulic-structure failure. Although the vortical fields associated with piers and abutments have been studied extensively in isolation, their coupled effect on coherent turbulence and sediment entrainment remains insufficiently clarified. This study evaluates the predictive capability of turbulence diagnostics obtained under rigid-bed conditions, prepared after prior mobile-bed experiments, by organizing all results along four longitudinal transects (Rows 1–4) to ensure direct comparability between hydrodynamic parameters and scour patterns. High-resolution Acoustic Doppler Velocimeter (ADV) measurements collected across multiple depths and cross-sections were used to quantify turbulence intensities, Reynolds shear stress (RSS), quadrant events, and sweep-to-ejection (STE) dynamics around a rectangular abutment and two circular bridge piers. The results demonstrate that the narrow interaction zone between the abutment and the upstream pier constitutes the dominant source of three-dimensional turbulence. Elevated near-bed RSS and strongly dominant sweep (Q4) events in this region represent the principal drivers of sediment entrainment, while the vertical concentration of turbulent energy close to the bed is shown to be more decisive for scour initiation than the magnitude of vertical velocity alone. This critical zone corresponds directly with the deepest scour measured in the mobile-bed tests. Downstream, turbulence progressively weakens, ejection (Q2) events become more prominent, and reductions in RSS and STE coincide with decreasing scour potential toward the second pier and the flow-recovery region. The unified presentation of results along four longitudinal transects confirms that RSS distributions, Q4–Q2 bursting behaviour, and STE profiles obtained under fixed-bed conditions provide robust, physically consistent predictors of scour in compound pier–abutment systems. These findings also strengthen recent hydrodynamic frameworks by confirming that pier–abutment spacing fundamentally governs vortex interaction and near-bed momentum transfer. The insights gained here offer improved guidance for scour prediction and the resilient hydraulic design of bridge foundations in fluvial and coastal environments.

Local scour around bridge foundations remains a major threat to structural stability, particularly when bridge piers and abutments are placed within the same contracted flow region. This study experimentally investigates the temporal evolution and final morphology of clear-water scour around coupled pier-abutment configurations, with emphasis on the combined effects of pier-abutment spacing and blockage ratio. The experiments were conducted in a recirculating laboratory flume using a rectangular vertical-wall abutment and single and double-pier arrangements. The results show that pier-abutment spacing has a non-monotonic effect on abutment scour. At the closest spacing ( $$x/{D}_{\text{p}}=1.5$$ x / D p = 1.5 ), the pier partially shields the abutment by reducing the direct erosive action of the approach flow. In contrast, the intermediate spacing ( $$x/{D}_{\text{p}}=3$$ x / D p = 3 ) produces the most severe abutment scour because of constructive interaction between pier-induced and abutment-induced flow structures. Under this condition, the maximum abutment scour depth increases by 10.9% compared with the close-spacing configuration and by up to 55% compared with the far-spacing ( $$x/{D}_{\text{p}}=6$$ x / D p = 6 ). Increasing the blockage ratio further intensifies scour, raising the maximum scour depth by approximately 7.4% at the abutment and 10% at the first pier. The temporal scour response follows a clear biphasic pattern, with 65–75% of the maximum scour depth developing during the initial 10–15% of the test duration, followed by a slower asymptotic approach toward equilibrium. The final scour morphology reveals pronounced upstream–downstream asymmetry, with deeper upstream scour holes controlled by downflow and horseshoe-vortex action and shallower downstream depressions associated with wake vortices and sediment redistribution. These findings demonstrate that pier-abutment spacing and blockage ratio jointly control both the rate and magnitude of scour development, highlighting the need to consider their combined effects in bridge-foundation design and scour-risk mitigation.