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A surge tank, as one of the most common control facilities, is applied to control head pressure levels in long pressurized pipelines during the water hammer occurrence. The cost-effective operation of surge tanks is highly affected by their characteristics (i.e., surge tank diameter and inlet diameter of surge tanks) and can effectively reduce the repercussion of water hammers. This investigation utilized the method of characteristics (MOC) in order to simulate the behavior of transient flow at the surge tank upstream and the head pressure fluctuations regime for the hydraulic system of a hydropower dam. Firstly, the MOC model was validated by experimental observations. The various types of boundary conditions (i.e., sure tank, reservoir, branch connection of three pipes, series pipes, and downstream valve) were applied to investigate the simultaneous effects of the surge tank properties. In this way, all the simulations of water hammer equations were conducted for nine various combinations of surge tank diameter (D) and inlet diameter of surge tank (d). The results of this study indicated that for the surge tank design with D = 6 m and d = 3.4 m, head pressure fluctuations reached the minimum level in the large section of the pipeline which is the surge tank upstream. Additionally, the occurrence of the water hammer phenomenon was probable in the initial section of the pipeline.

In urban wastewater collection and drainage networks, vortex structures are recruited to transfer fluid between two conduits with significant level differences. During the drop shaft, in addition to preventing the fluid from falling due to vortex flow formation, a significant amount of the fluid energy is dissipated due to wall friction of vertical shaft. In the present study, by constructing a physical model with a scale of 1:10 made of Plexiglas, the energy dissipation efficiency in the vertical shaft has been investigated. In this way, the performance of dimensional analysis indicates that the flow Froude number (Fr) and the ratio of drop total height to shaft diameter (L⁄D) are parameters affecting the efficiency of flow energy dissipation in the vertical shaft (ηs). This research considers four levels of Fr factor (1.77, 2.01, 2.18, and 2.32) and three levels of L⁄D factor (10, 13, and 16). Additionally, four replications for 12 possible combinations allow us to carry out 48 experiments and the full factorial method. The results demonstrated that the energy dissipation efficiency in the vertical shaft changes varies from 10.80 to 62.29%. Moreover, ηs values decrease with an increase in Fr whereas the efficiency increases with increasing L⁄D ratio. Furthermore, the regression analysis gave a second-order polynomial equation which is a function of Fr and L⁄D to accurately estimate the flow energy dissipation efficiency in the vertical shaft.