弯曲河道漂浮物阻滞作用下桥墩周围三维水流特性研究OA

In mountainous medium and small rivers,floating debris frequently accumulates upstream of bridge piers located in curved channels,significantly altering the local flow structure.To investigate the hydrodynamic characteristics around bridge piers under debris-blocked conditions,a three-dimensional numerical model was developed to analyze the effects of the oblique angle(θ),Froude number(Fr),and blockage ratio(Sw)on the longitudinal water surface profile,surface gradient,and three-dimensional velocity distribution near bridge piers.The results indicate that the oblique angle plays a critical role in determining local backwater elevation.As the oblique angle increases,the lateral interception of floating debris by the pier intensifies,exacerbating local backwater and reducing the water surface gradient.Within the bend angle range of φ=45～60°,the drawdown of the water surface becomes more pronounced,and the attenuation of the surface gradient is further amplified.Moreover,the presence of debris enhances vertical circulation and lateral flow diversion,prolongs the vertical adjustment of the flow,and results in a distinctly anisotropic velocity distribution.Under high Froude number conditions,increased flow inertia suppresses backwater development,leading to a reduced backwater height upstream of the pier and a notable increase in flow velocity around it.However,the obstruction caused by floating debris hinders the efficient conversion between kinetic and potential energy,causing a concentrated energy release toward the convex bank.This induces severe localized drawdown and a sharp increase in the water surface gradient.The velocity field exhibits high-gradient shear characteristics,with intensified velocity gradients in the middle layer and a weakened yet extended recirculation zone near the bed.Consequently,the recirculation region downstream of the bridge pier expands in both extent and intensity.The presence of floating debris amplifies the blocking effect of the pier,resulting in a more substantial water level drop and an increased disparity in surface gradients between the concave and convex banks.Under the combined influence of centrifugal force and pier resistance,variations in the water surface gradient along the convex bank exhibit a delayed response compared to those along the concave bank.Furthermore,under the coupled effects of constrained vertical momentum exchange and elevated turbulence intensity,the spatial structure of the velocity field is reconfigured,forming a vertically stratified pattern characterized by concentrated flow in the surface layer and attenuated flow near the bed,while the recirculation zone continues to expand.These findings provide a scientific basis for flood control design and mitigation of bridge damage in mountainous medium and small rivers.