Analysis of Flow Pattern with Low Reynolds Number around Different Shapes of Bridge Piers, and Determination of Hydrodynamic Forces, applying Open Foam Software

Abstract

In many cases, a set of obstacles, such as bridge piers and abutments, are located in the river waterway. Bridge piers disrupt the river's normal flow, and the created turbulence and disturbance causes diversion of flow lines and creates rotational flow. Geometric shape and position of the piers with respect to flow direction and also the number of piers and their spacing are effective in changing the river-flow conditions, such as the formation of vortices, their breakdown and hydrodynamic forces exerted on the piers. This article has been performed by applying the two-dimensional, open-source, OpenFOAM software. For this purpose, after selecting the grid size in GAMBIT software, different pier shapes were examined , considering different Reynolds numbers, and formation of the flow pattern, Strouhal number, vortex magnitude, and drag and lift coefficients for each pier shape were specified. Results for three different pier shapes indicated that in Reynolds number of 200, the highest drag coefficient (1.82) and maximum flow velocity (1.55 m/s) correlated to the square pier. The lowest drag coefficient (0.46) was calculated for the rectangular pier (having a semi-circular edge on one side and a sharp-nose edge on the other side) when the flow collides with the semi-circular edge. The least drag and lift forces are exerted to the rectangular pier, as compared to other pier shapes. The lowest lift coefficient (0.012) was obtained for a rectangular pier. On the other hand, the position of the sharp-nosed edge in the wake region caused the vortex shedding to occur at a greater distance from the pier.