Experimental study on the water and sediment characteristics in a trapezoidal desilting channel with a swirling flow generator

In order to discover the water and sediment characteristics of trapezoidal desilting channel with a swirling flow generator (TDCSFG) under different water and sediment conditions, adopted the method of model test, the water and sediment movement rule and sediment discharge characteristics of TDCSFG under different water and sediment conditions such as incoming flow rates, mass of added sediment, median particle size of inflow sediment and inlet flow velocities were studied, and its split ratio, distribution of water consumption, sediment trapping efficiency and residual sediment efficiency were analyzed. The results show that the water consumption for sediment discharge was small, the effect of desilting was remarkable. When the flow rate or inlet flow velocities increased, the sediment carrying capacity of water flow increased, the amount of suspended-load sediment increased, the bed-load sediment in the bottom water layer decreased, the sediment trapping efficiency of TDCSFG decreased, and the residual sediment efficiency increased, which has obvious influence on the sediment discharge effect. Under experimental conditions, when the incoming flow rates increased from 30 m³/h to 90 m³/h or the inlet flow velocities increased from 0.57 m/s to 1.60m/s, the sediment trapping efficiency decreased from 92.97% to 76.16% and 92.97% to 79.77% respectively, and the variation range of sediment interception rate was 16.81% and 13.20% respectively, the maximum residual sediment efficiency increased from 5.28% to 21.38% and 5.28% to 18.77% respectively, and the variation range of residual sediment efficiency was 16.10% and 13.49% respectively. and its influence was mainly concentrated in the sediment with the particle size range of >0.075～0.315 mm. Under experimental conditions, when mass of added sediment was increased from 300g to 700g or median particle size of inflow sediment was increased from 0.315mm to 1.250 mm, the content of particle-size sediment in the lower flow increases, and the bed-load sediment increased. The sediment-carrying force generated by the flow can only carry part of small-size sediment into the downstream channel, and the sediment trapping efficiency of TDCSFG increased and the residual sediment efficiency decreased, the sediment trapping efficiency increased from 92.97% to 95.27% and 89.53% to 95.83% respectively, and the variation range of the sediment interception rate was only 2.63% and 6.33%, the maximum residual sediment efficiency decreased from 5.28% to 2.85% and 8.64% to 3.59% respectively, and the variation range of residual sediment efficiency was 2.43% and 5.05% respectively. It shows that the change of mass of added sediment and median particle size of inflow sediment has little influence on the sediment discharge effect of TDCSFG, most of the sediment with the particle size range of > 0.160～1.250 mm can be discharged. TDCSFG has great sediment discharge effect under different water and sediment conditions, and the minimum sediment trapping efficiency was 76.16%, and the sediment trapping efficiency was not less than 94.88% for sediment particles with a particle size >0.600～3.000mm, so it can effectively discharge harmful sediment in the channel. Compared with the rectangular cross-section channel with the same flow rate or the same median particle size of inflow sand, TDCSFG kept the similar Sediment trapping efficiency and reduces the split ratio by 6.43 ～ 16.66%. After increased the inclination angle in the closed end of the sediment transport pipe, the problem of sediment accumulation was improved, and there was no palpable phenomenon of sediment accumulation at the bottom of the upstream and downstream channels, swirling flow generator and in the sediment transport pipe, effectively improve the efficient utilization of water and sediment resources. This study makes clear the suitability and high efficiency of trapezoidal desilting channel with a swirling flow generator, which can provide reference for its future application in engineering.