Experimental Study of the Roughness Bed with Non-Continuous Trapezoidal Elements on S-Jump Characteristics in the Non-Prismatic Rectangular Channel

Depreciation of kinetic energy of flow in the stilling basin is one of the most important topics considered by hydraulic engineers. Since hydraulic jump has known as one of the important factors to energy loss in the stilling basin, it is important to form and control it in the basin. The use of expanding section can be one of the ways to ensure the formation of a jump in the basin. This way in comparison to the prismatic channels, increased energy loss of current and reduced the secondary depth and the length of the hydraulic jump. On the other hand, given that the rough bed decreases the secondary depth and the jump length, in the present study, S-jump characteristics on non-continuous trapezoidal roughness elements at two relative roughness height of 1.15\leH/y1\le1.68 and 2.3\leH/y1\le3.37 in the non-prismatic channels were analyzed. The experiments were performed in a in the horizontal rectangular channel which is 30 cm wide, 45 cm deep and 5 m long. A total of 99 experiments were carried out in prismatic channels and non-prismatic channels with expanding ratios of 0.67, 0.5 and 0.33 and range of Froude numbers from 4 to 12. The results of present study show that the shear stress of rough non-prismatic channels in relative height of roughness elements of 1.15\leH/y1\le1.68 was about 11.12 times that on the smooth prismatic channels. Also, rough bed caused a 12 to 17 percent reduction in the conjugated depth and a 7 percent decrease in jump length in comparison to the smooth bed. For the relative height of 2.3\leH/y1\le3.37, the shear stress of a rough non-prismatic channels was 13.2 times that on smooth prismatic channel. The conjugated depth and length of jump in the rough expanding section decreased by 20-30\% and 13\% respectively. The rough non-prismatic channel at an expanding ratio of 0.33 in comparison to smooth prismatic channel caused 59.5\% reduction in the secondary depth and increased jump efficiency about 29\%.