| In recent years,water diversion through channels has become one of the important methods for solving the problem of the imbalance between supply and demand of water resources in China.As the sediment content of rivers in China is generally high,the hydraulic mechanical erosion,channel deposition and other phenomena often occur due to excessive sediment introduction during water diversion.In order to solve the problem of difficult separation of water and sediment in the process of water diversion,a new type of sediment treatment facility,desilting channel with a swirling flow,was proposed based on the characteristics of the strong sediment carrying capacity of swirling flow.As a new expelled sediment technology,the effects of different body type conditions,different hydraulic conditions and different sediment conditions on the sediment characteristics of the desilting channel with a swirling flow are not clear,but these are the key factors for its wide application.In order to clarify the variation rules of the sediment characteristics of the desilting channel with a swirling flow under different influencing factors,some expelled sediment experiments were carried out under different body shapes,different hydraulic conditions(inflow rate,inflow velocity,downstream hydraulic conditions)and different sediment gradation,studied its water and sediment characteristics parameters,such as channel and sediment transport pipe flow pattern,split ratio,sediment trapping efficiency,expelled sediment mass,residual sediment mass,deposited sediment mass,etc.At last,the suitability of the desilting channel with a swirling flow under different body shapes,different hydraulic sediment conditions was analyzed.The main research results are as follows:(1)The research results of expelled sediment experiments with different body shapes indicate that:The split ratio of desilting channel with a swirling flow and the rotation strength of water flow in sediment transport pipe are closely related to the width of inlet and outlet of swirling flow generator and the diameter of sediment transport pipe.Under each operating condition,compared to body shape one,the split ratio of body shape two is smaller,resulting in better water-saving performance;the water surface line in the channel is higher,and there is no local flow pattern change in the transition from slow flow to rapids flow in the channel section of the sediment transport pipe.Meanwhile,high strength rotating flow with through cavity is formed in the transport pipe section,which is more conducive to sediment expelle.Both of the two shapes of desilting channel with a swirling flow can effectively expelle large particle size sediment above 0.315mm,and the sediment trapping efficiency of body shape one is slightly higher on the whole.Taking the upstream channel flow rate Q=50m3/h and the median particle size of incoming sediment d50=0.6mm as an example,compared with body shape Ⅰ,body shape Ⅱ reduces water consumption for expelle sediment,split ratio and deposite sediment mass by 6.48m3/h,13.25%and 2.66g respectively.The sediment trapping efficiency of Shape one and Shape two are 93.77%and 92.03%respectively,and the downstream sediment of both shapes of channels is mainly composed of extremely fine sediment with a diameter of(0.075～0.315)mm.(2)By comparing the variation rules of sediment discharge characteristics under different hydraulic conditions of the desilting channel with a swirling flow with body shapes two,it can be seen:When the upstream flow or velocity increases,it mainly affects the effect of desilting channel with a swirling flow on the expelle of fine particle size sediment in the range of(0.075～0.315)mm,resulting in the reduction of sediment trapping efficiency,the reduction of expelle sediment mass,and the increase of residual sediment mass.The mass of deposited sediment in the sediment transport pipe is proportional to the incoming flow rate and inversely proportional to the incoming flow rate,but the maximum deposited sediment mass under each hydraulic condition is 7.68g,which only accounts for 2.6%of the total mass of incoming sediment.When the median particle size d50=0.6mm graded sediment was expelled,the maximum amplitude of sediment trapping efficiency is 16.25%in the experimental groups with different inflow rates.In the experimental groups with different inflow velocity,the sediment trapping efficienc is higher than 76.86%,and the maximum variation is 9.91%,indicating that the influence of changing inflow rate on sediment discharge characteristics is more obvious.The sediment discharge performance of the desilting channel with a swirling flow was further improved to install the water eliminator in the downstream of the channel,especially in the discharge of sediment within the particle size range of(0.16～0.315)mm.(3)The results of sediment discharge experiments under different sediment grading conditions indicate that:when the sediment particle size range is constant,the performance of desilting channel with a swirling flow is weakened with the decrease of the median particle size of incoming sediment,but it can still effectively discharge the large particle size sediment which is more harmful in the flow.Under each sediment inflow conditions,the maximum variation amplitude of sediment trapping efficiency was 20.78%,and the interception rate of desilting channel with a swirling flow for sediment with particle size above 0.315mm is all higher than 82.9%,and the total deposited sediment mass is between(1.71～7.56)g,the ratio of small and medium-sized particle size sediment deposition to total sediment deposition within the range of(0.075～0.6)mm decreases from 73.59%to 14.92%with the increase of the median particle size of the incoming sediment.In summary,the desilting channel with a swirling flow has obvious sediment separation phenomenon,which can effectively discharg the harmful large particles of sediment in highly concentrated water flow,so as to achieve the purpose of diverting and discharging sediment.During engineering design,the shape parameters of swirling flow generator and sediment transport pipe can be changed to obtain the shape structure with smaller deposited sediment mass and lower water consumption rate on the premise of ensuring higher sediment trapping efficiency.At the same time,the overall sediment discharge performance of the desilting channel with a swirling flow can be improved by optimizing channel flow rate,velocity and downstream hydraulic conditions.The research has clarified the variation rules of sediment characteristics of desilting channel with a swirling flow under different influencing factors,and the results can provide a reference for its design and application in engineering. |
