Experimental Study of 3D Flow Field and Scour in a 90 Degree Bend

Flow is affected by both the pressure gradient and the centrifugal forces in the bend of rivers and their interaction leads to secondary flow. In this study the flow field and scour in a 90 degree bend were experimentally measured. Experiments were carried out in a channel with mild curvature. A three-dimensional Acoustic Doppler Velocimeter (ADV) was used for measuring the flow field. Also, a laser bed profiler was used for measuring the variation of bed topography. The results show formation of a main secondary flow in the bend and another second secondary flow near the outer bank. The direction of the second secondary flow is opposite to the direction of the main secondary flow. This flow pattern is evident from the middle sections of the first half of the bend up to the end of the bend. The results of flow pattern and bed scour were also addressed. In addition, the vortices in the bend, the changes in the secondary flow and the vortices and the scour pattern at the outer bank and sedimentation at the inner bank are investigated.