The effect of collar width ratio on the flow pattern around an oblong pier in a bend

In this paper, the effect of collar width ratio on the flow pattern around an oblong pier in a 180-degree channel bend was experimentally studied. This channel has a rectangular cross section. It is 1 m in width and 0.7 m in height. The upstream and downstream paths are respectively 6.5 and 5 m long. The ratio of the bend's central curvature radius to the channel width is 2; hence, it qualifies as a sharp bend. Experiments were carried out under clear water approach flow conditions. The results showed that the presence of collars around an oblong pier creates vortices in the opposite direction of the longitudinal flow, causes the distortion and disturbance of the streamlines toward the pier downstream, and decreases downflow strength in front of the pier nose. Furthermore, doubling the collar width results in 0.93 and 0.68 times the vorticity and the power of the secondary flow on the pier upstream, respectively. It also reduced the maximum values of the Reynolds stresses perpendicular to the y-plane in x direction and perpendicular to the z-plane in y direction by respectively 45 and 60%, and increased the Reynolds stress perpendicular to the z-plane in x direction by 25%. HIGHLIGHTS Experiments were carried under clear water conditions.; Doubling the collar width resulted in 0.93 times the vorticity.; Doubling the collar width has increased the Reynolds stress on zx by 25%.; The maximum vertical velocity has decreased by about 15% by doubling the collar width.; Increasing the collar width around the pier increases the maximum turbulence kinetic energy values by 50%.