Hydraulic Jump Investigation in Compound Channel with Irregular Roughness Arrangement Under Various Geometric and Hydraulic Conditions

Hydraulic jump, a rapidly changing flow phenomenon, has been encountered in many practical applications and refers to the transition of flow from supercritical to subcritical state. When water reaches a section of the channel with a supercritical flow regime and needs to undergo a change in state due to specific channel characteristics and position, the depth of flow increases significantly over a relatively short distance, resulting in a noticeable energy dissipation and a considerable reduction in velocity. On the other hand, composite channels, due to their different hydraulic and geometric conditions in the main channel and floodplain sections, bear closer resemblance to natural channels. This research focuses on investigating hydraulic jumps in compound channel with irregular roughness arrangements under various geometric and hydraulic conditions using Flow-۳D. The width and depth of the main channel are kept constant, while the width of the floodplains varies in three values: ۱۸ cm, ۲۲.۵ cm, and ۴۵ cm. Simulations are conducted for three depth ratios, three roughness height ratios, and three different velocities. The irregular roughness elements in the form of small cubes are embedded in the channel bed in a zigzag pattern. According to the simulation results, the presence of roughness elements leads to a reduction in the secondary jump depth compared to the smooth case. For instance, with a floodplain width of ۱۸ cm, a depth ratio of ۳.۰, a roughness height ratio of ۲, and a velocity of ۵.۳ m/s, the average secondary depth decreases by approximately ۶۴.۵% compared to the smooth channel. However, with an increase in the floodplain width to ۴۵ cm, the reduction in the secondary jump depth is about ۵۹.۱۲%. The minimum value of the secondary-to-initial jump depth ratio is observed at a relative depth of ۶.۰ and a roughness height ratio of ۲. Furthermore, it is observed that the jump length significantly decreases with an increase in the roughness height ratios for smaller depth ratios. The jump length decreases by approximately ۲۲.۵% at the minimum value of the roughness height ratio, with a floodplain width of ۱۸ cm, a velo

کلیدواژه ها:

Hydraulic jump ، irregular roughness ، composite section ، jump length ، relative depth