Numerical Investigations of the Bridge Pier Shape Influence on the Bed Shear Stress

 

Bouabdellah Guemou

Academic center of Ain Temouchent
Ain Temouchent, Algeria
e-mail: gomane8@yahoo.fr

Abdelali Seddini

Department of Hydraulics, University of Tlemcen, Algeria
e-mail: abdelseddini@yahoo.fr

Abderrahmane Ghenim

Department of Hydraulics, University of Tlemcen, Algeria
e-mail: anghenim@yahoo.fr

 

 ABSTRACT

Reduction of the scour around obstacles has taken too much research, numerical and experimental researches on the subject have been carried out and few countermeasures have been proposed. Existing literature revealed that the shape of the obstruction to the flow can strongly affect the flow pattern around it and the strength of the down-flow, horseshoe vortex and the wake vortex are greater in the case of square piers compared to circular piers. Few studies have been reported on the local scour around non-circular piers such as round-nosed piers. In the present numerical investigations, the effect of the pier shape is reported. We have studied the influence of the aerodynamic shape of the bridge pier on the down-flow intensity and the bed shear stress. For that purpose, a number of simulations have been carried out using a Finite volume method (FVM). The geometric configuration consists of a bridge pier (cylinder and round-nosed pier) fixed in a domain (Water), mesh is more concentrated around the pier because of the flow pattern in this area and along simulations we have used 3D unsteady model. For the turbulence model we have choose the Detached Eddy Simulation (DES) for his capability to capture the rich dynamics of the horse shoe vortex at the upstream junction between the pier and the bed. The present parametric study showed that with a constant bridge pier width, the aerodynamic shape of the round-nosed pier studied in this paper; reduce better the shear stress at the upstream junction between the pier and the bed than the circular bridge pier. Also, fluctuations in the bed shear stress value observed in the circular case are reduced in the round nosed shape. The discussion of the relation between the bridge pier shape and the bed shear stress proposed in this paper is promising and experimentations in that field provide more details that can help to control the scour around bridge piers.

Keywords: Bridge Piers; Local Scour; Aerodynamic Shape; DES Simulations; Circular Pier; Round-Nosed Pier; Parametric Study

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