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Stilling basins with sudden expansions are one of the energy dissipation structures. In the hydraulic jump, pressure fluctuations cause significant damages in stilling basins by cavity formation, erosion, and vibration. Roughness can also lead to changes of the behavior of stream lines and vortices. Despite the large number of works on the topic, the role of roughness in spatial hydraulic jumps is not yet fully understood. Present research aimed to study the influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 within the range of Froude numbers, 2 to 9.5. The results showed that roughness decreases intensity of pressure fluctuations in an abrupt expansion stilling basin. Additionally, in sudden expanding sections, the energy loss increases, and the intensity of pressure fluctuations decrease due to the formation of lateral vortices. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively. The results revealed the clear dependence of these variables on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385, where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins in this range. [ABSTRACT FROM AUTHOR]

The effect of fluctuating pressures due to turbulence on the hydraulic jump causes significant damage to the relaxation pool. Moreover, the presence of roughness in the bed changes the behavior of flow lines and the formation of vortices during the jump. Therefore, the aim of this study was to determine the effect of the presence of roughness on hydrodynamic pressures in type S hydraulic jump in sudden divergence sections. For this purpose, experiments were performed in a relatively large channel with a width of 0.8 and a length of 12 m in the calm pool with divergence ratios of 0.33, 0.5, 0.67 and 1 in the range of Frued numbers between 2 to 9.5. Roughness elements with a height of 3 cm and specified distances were placed in the channel bed and downstream of the divergence section. In order to determine the effects of roughness on the level of hydrodynamic pressures, the experiments were performed in two separate stages, including a completely flat pool bed without the presence of roughness in the first stage (77 experiments) and with the presence of roughness in the pool floor in the second stage (81 experiments). The results showed that the presence of roughness in the bed reduces the intensity of pressure fluctuations in the relaxation pool. In addition, in sudden divergent sections, due to the formation of lateral vortices, the energy drop increases and the intensity of pressure fluctuations decreases. The maximum reduction rates of pressure fluctuations were estimated to be 27, 46 and 58% for the divergence ratios of 0.67, 0.5 and 0.33 in the rough bed, respectively.

Stilling basins with sudden expansions are one of the energy dissipation structures. In the hydraulic jump, pressure fluctuations cause significant damages in stilling basins by cavity formation, erosion, and vibration. Roughness can also lead to changes of the behavior of stream lines and vortices. Despite the large number of works on the topic, the role of roughness in spatial hydraulic jumps is not yet fully understood. Present research aimed to study the influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 within the range of Froude numbers, 2 to 9.5. The results showed that roughness decreases intensity of pressure fluctuations in an abrupt expansion stilling basin. Additionally, in sudden expanding sections, the energy loss increases, and the intensity of pressure fluctuations decrease due to the formation of lateral vortices. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively. The results revealed the clear dependence of these variables on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385, where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins in this range.