One-way surge tank protection of sediment-laden water hammer on long-distance water supply projects

Abstract The safety and stability of long-distance water supply projects can be closely related to the reasonable protection of water hammers. However, the traditional transient flow in the method of characteristic cannot consider the influence of natural water sediment particles on the evaluation of water hammer protection. In this study, the pipeline head loss model was constructed, according to the sediment-laden water pipeline resistance model of Chen Guangwen and the single particle settlement formula of Zhang Ruijin. The method of characteristic was improved to simulate the sediment-laden water hammer pressure, according to the wave velocity formula of the water hammer on the slurry by Han Wenliang and the equivalent friction formula of sediment-laden water pipeline flow. The improved model was validated by the pressure data of reservoir-pipe-valve (RPV) water hammer closing valve test with water. The pressure of the sediment-laden water hammer with the low-concentration particle parameter was close to the experimental value of water. Combined with the boundary conditions of a one-way surge tank, one specific pipeline system of the water supply project was selected to determine the effect of sediment with different concentrations and particle diameters on water hammer protection under different initial pump heads. The results show that when the pump head of sediment-laden water was adjusted until the water level of downstream reservoir is consistent, the internal water pressure along the pipeline was higher, because of the higher initial pump head with sediment-laden water. After the power failure and pump stopped, the pressure dropping behind the pump of sediment-laden water was larger than that of water, and the minimum internal water pressure of sediment-laden water along the pipeline was lower than that of water. The lowest pressure at the node behind the pump was -15.76 m, whereas there was -37.82 m along the pipeline. The internal water pressure along the pipeline was greater than 0m under the original one-way surge tank protection. In the sediment-laden water, the minimum pressure decreased gradually with the increase of particle diameters and sediment concentrations, where the minimum reached -2.41 m. Except for some conditions with the low concentration particle parameter (S＜10 kg/m3, d=0.01 mm), the negative pressure occurred along the pipeline of sediment-laden water, and the minimum pressure points were always located 19.7 km behind the pump. Therefore, there was different influence of sediment particles on the minimum internal water pressure at different positions of the pipeline. In order to increase the internal pressure along the pipeline, the water make-up capacity of the one-way surge tank should be increased. As such, the one-way surge tank protection scheme was obtained for the sediment-laden water. There was no negative pressure along the pipeline of sediment-laden water under the particle parameters conditions of S=100 kg/m3 and d=0.1 mm. The pressure deviation of the pipeline before 10.5 km was small, not more than 1 m, and then exceeded 2.5 m within the range of 11.3-21.8 km, compared with the minimum internal water pressure along the pipeline of the two protection schemes. The maximum pressure deviation reached 3.29 m at the point 21.8 km behind the pump. The method of characteristic was of great significance to improve the numerical simulation of multiphase transient flow. The finding can provide a strong reference for the sediment-laden water hammer protection and stable operation on long-distance water supply projects of high sediment concentration basins.