Research On Resistance Characteristics Of Hydraulic Lifting Of Sediment In Elbow Pipe

In the rescue dredging project,the sediment is transported to the shore base through the pipe,which is often accompanied by the change of spatial attitude of the pipe and the existence of a certain height difference,elbow pipe can realize the corner transition of sediment conveying process resulting in the problem of high resistance and easy blockage of the particles in the pipe.In this paper,the hydraulic lifting process of liquid-solid two-phase flow 90°elbow pipe is taken as the research object,and the conclusion that the height ratio of solid-phase bed layer and liquid-phase surface layer measures the particle retention characteristics is drawn,in order to reveal the resistance characteristics of liquid-solid two-phase flow conveying process under the action of particle flow,and provide some theoretical basis for the minimum flow velocity requirement and power requirement of conveying process.The main research contents of this paper are as follows.（1）Construct the elbow pipe hydraulic lifting liquid-solid two-phase flow model.Establish the physical model of 90°elbow pipe and clarify the boundary conditions of numerical simulation,clarify the liquid-phase motion model and solid-phase motion and collision contact model,obtain the inter-phase tracing force of liquid-solid two-phase flow,analyze the characteristics of single-phase flow boundary layer motion,establish the surface layer model under the action of particle flow,analyze the force characteristics of solid-phase particles in particle aggregation area and contraction tube area under the influence of surface layer,and clarify theoretically the mechanism of particle stagnation.（2）To reveal the flow characteristics of liquid-solid two-phase flow at the bend and lifting section,and to clarify the critical non-clogging flow field conditions.Through the coupled CFD-DEM numerical simulation of sediment lifting process in the elbow pipe,the solid-phase flow characteristics at the bend are clarified from the solid-phase volume fraction distribution law and velocity fluctuations at local sampling points in the fluid domain,The solid-phase flow characteristics of the lifting section are revealed from the liquid-phase velocity distribution,particle motion scale and overall transport trend,and the flow field characteristics of the particle population formed by solid-phase deposition are analyzed,and the conclusion that the critical transport conditions are characterized by the proportion of solid-phase bed height at the bend and the proportion of liquid-phase attachment layer height at the lifting section is obtained,results show that the critical state value of overall non-deposition at the bend is under the condition of particle bed height ratio h₁/D=0.32,and the critical state value of overall non-deposition at the lifting section is under the condition of attached surface layer height ratio h₂₁/D=0.245 under the set particle value parameter.（3）The changes of critical flow velocity and drag characteristics under the influence of multiple parameters are obtained,and the critical flow velocity prediction model is constructed.Numerical simulations of the hydraulic lifting process under different flow velocities,bend-diameter ratio r/D,particle particle size D_pand solid phase transport volume Q_mwere conducted to analyze the change law of pressure field in fluid domain under the influence of multiple parameters under the action of particle swarm,and the results showed that:under the action of particle flow,the flow velocity has the most significant pressure loss near the critical state value,and under the same conditions,the extreme value of pressure loss appears when the bend-diameter ratio r/D=2,while The degree of influence on the drag loss under four factors was analyzed by the extreme difference analysis table of the orthogonal experiment:mass flow rate>conveying speed>particle size>bending diameter ratio.Based on the critical state value,the change of critical flow rate under different parameters is obtained,and the influence law of each parameter on the flow condition of two-phase flow conveying is analyzed.The critical flow rate prediction model is established byπtheorem,and the safety coefficient correction model without blocking and reducing energy dissipation is introduced according to the pressure loss change.（4）To rescue dredging mobile pump truck as the engineering background to build a pipeline conveying experimental platform,collect flow,pressure and other relevant flow field data,and analyze the experimental conditions in different flow rates and conveying volume conditions in the lifting process of mass flow and pressure loss change law.