Abstract
A small aspect ratio of submerged vanes when used near the outer bank at the angle of attack between 10° to 20° and at the initial height above the bed between 20-40% of flow depth is considered one of the most successful river training structures. Vanes when located within the bends of river, produces helical swirls at inverse action with the centrifugally secondary current action. Accordingly, its existence leads to mitigate the influence of the secondary current, thus reducing the outer bank erosion. The present study aims to investigate the effect of distance which measured from the outer bank (δb) on the hydraulic performance of vanes when it arranged at a specified configuration within 180° bend. As a result, when the submerged vanes have been installed at δb/b = 0.25 within the third to the fifth sectors of bend and δb/b = 0.1 within the sixth sector at a zigzag pattern led to lesser outer bank scour with the Percentage Improvement (PI-indicator) equal to 72.71%.
Highlights
In river reaches when flow passes through bends or meanders, the secondary current developed due to the combination of both transverse pressure gradient and centrifugal force
The outer bank of bend reach become subjected to the scour due to a high velocity component near the surface, while the low velocity component created near bed has the influence to transport the scoured particles from the outer bank towards the inner bank causes the deposition, this mechanism was stated by Odgaard and kennedy (1983; Odgaard and Spoljaric, 1986; Odgaard and Wang, 1991a; Marelius and Sinha, 1998; Voisin and Townsend, 2002) and many others before and thereafter
A major difficulty with these techniques is the lack of analytical tools for predicting their effectiveness and impact on the channel. Another technique consists of installing a small aspect ratio of submerged vanes on stream bed at 10°-30° angles of attack with the mean flow to counter the secondary current action
Summary
In river reaches when flow passes through bends or meanders, the secondary current developed due to the combination of both transverse pressure gradient and centrifugal force. The effect of vanes on scour and sediment control has tested by many researchers; Voisin and Townsend (2002) introduced the best dimensions of submerged vanes to protect the outer river banks in bend sections.
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