Experimental comparison of flow pattern around convergent-vertical and divergent-vertical pier groups located in a 180 degree sharp bend with streamwise direction

Abstract

ABSTRACT The flow pattern at the meandering rivers changes to a helical flow. The installation of bridge piers on the meandering river and collision of the flow with pier geometry creates a far more complicated flow. The experiments were performed in a 180-degree bend channel and a radius to curvature ratio of two. The pier groups were installed in convergent-vertical in streamwise direction (CVS) and divergent-vertical in streamwise direction (DVS). The results show that the earliest eddy flows in the convergent-vertical pier groups were formed at near water surface level. According to the findings, the formation of return flow from a 77.5 degree angle and at a distance of 35 to 45 percent of the width of the channel from the inner bank happened. However, the return flows were initiated from the 87.5 degree and at a distance of 60% to 70% of the width of the channel from the inner bank in the divergent-vertical pier group. The power of secondary flow in convergent-vertical and divergent-vertical pier groups occurred at 85 and 87.5 degree sections respectively, and equal to 3.5 and 1.25 times the pier diameter from the center of the piers’ location upstream.