انتون اشلایز

The complex interactions between streameise flow and curvature- induced secondary flow in bends, bed morphology cause erosion near the outer bank, and deposition near the inner bank, that it can endanger the outer bank’s stability and also reduce the navigable width of the rivers. There are several techniques to protect the outer bank, reduce adverse impacts and control bed erosion in bends. Methods used in most parts of the world include submerged groynes, spur dikes, and bandal-like structures. But, meny these Methods have the disadvantage of being fixed constructions on the bed river that caused a threat for navigation. This paper describes a new way that consists in changes the bed morphology with provoking changes in the flow pattern. Dugue, et al. (2011, 2012) studied morph dynamic bends rivers with the Air-bubble screen method. Their results reveal that the air bubble screen is able to modify the flow pattern by shifting the maximum scouring from the outer bank towards the center of the flume and does not endanger its stability anymore. Dugue et al, 2013 studied scour reduction at a 193° bend by an air-bubble screen method. Velocity pattern at 70° bend showed that the bubble-induced flow pattern overcame the secondary flow induced by the outer bank while decreasing the morphology slope. It also showed 50 percent reduction in the maximum scour depth. Shukry (1949) is one of the first researchers in the study of erosion of the outer bank of rivers in a canal with a 180- degree bend with various proportions of the rivers radius to its width. There have been very few investigations about air bubble screen in 90 bend, therefor  in this study the effect of the air bubble screen on flow pattern and Secondary flow strength  and bed shear stress in 90 degree bend under Froude numbers 0.45 is examine.

An air-bubble screen is an innovative technique for riverbank protection along the bends which improve the navigation conditions in the alluvial rivers. In this research, the effects of this structure on a 90° mild and long bend on the bed morphology and flow pattern have been investigated. To this end, the experiments were carried out with three angles 0, 45, 90 degree and four Froude numbers of 0.37, 0.41, 0.45, 0.47 combined with three air discharge. Experiments performed in a mild bend using clearwater showed that the bubble screen was able to redistribute the velocity patterns and bed morphology in the bend. In addition, the results showed that maximum bend scouring is reduced about 47% andoccurs further away from the outer bank and high velocity zone shifted toward the center of the channel. The results showed that the maximum and minimum scour depths in outer bank with 0 and 90 degrees angles respectively. Also, by increase of air discharge ratio the maximum scour depth was decreased.

In this study, the impacts of skew angle of two bridge piers with respect to the flow direction on the equilibrium scour depth in front of the piers under clear water condition is investigated. For this purpose, the piers are aligned with four different skew angles with respect to the flow direction. Additionally, to obtain the equilibrium scour depth in front of the piers, the experiments are performed until reaching the equilibrium time. The results show that increasing the skew-angle increases the equilibrium scour depth and time. The minimum and maximum equilibrium scour depths at both piers occur at the skew-angles of 0 and 60 degree, respectively. Regarding the analysis of the results, the maximum equilibrium scour depths in front of the piers, for the skew angles less than 28 degree occur at the upstream pier while for the skew angles greater than 28 degree is shifted to the downstream pier. In the following, formula are provided to estimate the scour depths in front of the piers, utilizing the Semi-logarithmic linear regression method and observed data.