Influence And Optimization Of Inclined Pipe Arrangement On Sediment Performance Of Yellow River In Gravity Sedimentation Tank

Object,The Yellow River has high sediment concentration,fine particle size,and obvious spatial and temporal differences,which is easy to cause the failure of irrigation system.The precipitation filtration is considered as an important measure to remove the Yellow River cement sand.Among them,the gravity sedimentation tank,as a primary filtration sedimentation equipment,can effectively remove the Yellow River cement sand particles.However,at present,the gravity sand sedimentation tank covers a large area and high construction cost seriously restricts its application,and the gravity inclined pipe sand sedimentation tank can effectively solve this problem,but the optimal layout form of the inclined pipe is still not clear,and the principle of inclined pipe sediment can not reach a consensus conclusion.Therefore,this thesis analyzes the sediment sedimentation effect of different inclined pipe structures,aiming to explore the optimal layout form of the inclined pipe,clarify the sedimentation effect of the sedimentation tank on the typical Yellow River sediment in different sections,the sediment sedimentation mechanism inside the inclined pipe,and the sedimentation principle of the gravity inclined pipe sedimentation tank.In order to provide reference and theoretical guidance for the sediment treatment of the Yellow River in the drip irrigation project.Methods,In this thesis,three kinds of inclined pipe layout forms(Fs,Fv1,Fv2)were designed,three typical Yellow River sediment(Su,Sm,Sd)in the upper,middle and downstream reaches were selected,and the prototype sediment test of gravity inclined pipe sand sedimentation tank was carried out under two kinds of operating flow(Qq,Qs).Analyze the concentration and particle size of the sediment along the course,explore the influence of the inclined pipe layout forms on the Yellow River sediment settlement,and explore the settlement characteristics of the three typical Yellow River sediment.At the same time,combined with the PIV,test and CFD numerical simulation results of the inclined pipe,the CFD-DPM numerical simulation model of water and sediment two-phase flow in the inclined pipe is established,and then explores the influence of the layout Angle and running flow rate on the flow characteristics and the sedimentation process of the inclined pipe,and reveals the sediment settlement mechanism of the inclined pipe.The CFD-DPM water-sediment two-phase flow numerical model is used to study the internal flow characteristics and sediment settlement characteristics of the three inclined pipe layout forms,which reveals the reasons for the difference of sediment settlement effect between different inclined pipe arrangements.Results,(1)In the process of settling the sediment of the Yellow River,a large amount of coarse grain sediment has settled before entering the inclined pipe.The inclined pipe mainly settles the sediment with lower concentration(1.06～3.01kg/m~3)and fine particles(d<75μm);for the typical Yellow River cement sand in the upper,middle and downstream reaches of the Yellow River,the outlet sediment content is0.342～1.354kg/m~3 and the outlet sand grain content is 0～0.018kg/m~3.(2)The different inclined pipe arrangements differ in the Yellow River sediment settlement capacity significantly(P<0.05),and the V-shaped inclined pipe is better than the conventional inclined pipe,and the Fv2 inclination of 60°and 45°is taken as the optimal combination.Among them,the outlet sediment content of Fv2 was 0.342～0.991kg/m~3,which decreased by 10.01%～20.95%and 26.82%～38.83%compared with Fv1 and Fs,respectively.The sedimentation effect of the sedimentation tank on the three types of Yellow River sediment is different.The sediment content and its component content at the outlet is Su<Sm<Sd,the sediment deposition rate is lower than Sm and Sd,and the sand sediment deposition rate is higher than Sm and Sd.(3)Combined with PIV,the test and CFD-DPM numerical simulation results,it is found that the internal flow rate distribution of the inclined pipe decreases with the middle axis to the side wall of the inclined pipe,the high flow rate in the direction of the middle axis,and the low flow rate near the side wall of the inclined pipe.The internal movement characteristics of the inclined pipe of different particle sizes show that the coarse grain sediment moves to the inclined pipe,the fine particle sediment is concentrated in the mainstream area,and the very fine particle sediment moves along the upper wall of the inclined pipe.It is found that coarse grain sediment is prone to settlement,low flow rate condition is conducive to sediment settlement,appropriately reducing the inclination Angle of inclined tube is conducive to sediment settlement,and increasing the inclination Angle is not conducive to sediment settlement.(4)The numerical simulation results of CFD-DPM show that the uniformity of water distribution and sediment distribution showed high flow rate area in the second half of the inclined pipe in the first half.Under different configurations,the water uniformity and sediment distribution of Fv 2 are best,followed by Fv 1and Fs;the maximum particle size of outlet sediment is the largest Fs,followed by Fv 1 and Fv 2.