Experimental Investigation on the Effect of Increasing the Collar Thickness on the Flow Pattern around the Oblong Pier in 180˚ Sharp Bend with Balanced Bed

In this paper, the effect of increase collar thickness has been investigated by considering other parameters affecting the flow pattern around the oblong bridge pier located at 90˚ from the 180˚ bend constant. Data acquisition was performed using the Vectrino 3D velocimeter. The leveling of the collar in both tests is constant and 0.4 times the pier diameter above the initial bed surface. The flow conditions were close to the motion threshold and bed balanced. The results showed that with an increase in the thickness of the collar by a factor of 4, the barrier surface is located in the flow path and the flow is deviated to the bed by colliding with the edge of the collar. This flow deviation that was due to the increase the collar thickness, led to 30% increase in the maximum depth of the scour hole upstream of the pier. Also, with the increase in the thickness of the collar, the tendency of the streamlines upstream of the pier to the inner bank increased, resulting in a 20% increase in the maximum sedimentation near the inner bank. The maximum turbulent kinetic energy at 80 degrees of the bend, corresponds with a protected pier with 3 mm thickness, equal to 620 cm2 /s2 .gr, which is reduced by 60% with increasing collar thickness.