Theoretical Study Of Particle Collapse Flow In Fluid Based On CFD-DEM Method

Gravity driven flow are widespread in nature,such as landslide,debris flow,pyroclastic flow,avalanche,or rockfall,etc,this kind of complex flow usually involves coupling movement with a large number of discrete solid particles and the complexity of the interstitial fluid,and it will also interact with the attributes of the flow field of different media,accompanied by complex stage such as instantaneous acceleration,deceleration,erosion and deposition.Among them,the interaction between particles and fluids is a very fundamental and important problem for the in-depth understanding of complex flow.In this thesis,CFD-DEM numerical simulation method was used to study the flow process of particle column collapse in fluid,and the regimes characteristics and evolution mechanism of different collapse flow behaviors were systematically analyzed.On this basis,the scaling law of collapse distance and flow duration was established.The main work of this paper is as follows:Firstly,the CFD-DEM model of particle collapse in fluid was established,and the collapse process of particle columns with different height-width ratios in pure water was studied.By comparing with the results of dry particles,the influence of fluid on the apparent morphology,movement and evolution of physical and mechanical properties of the particle column after collapse was analyzed in detail.Secondly,based on two dimensionless parameters,Stokes number and particle fluid density ratio,the partitioning characteristics of particle collapse flow in fluid with different properties are discussed.The dynamic behavior,flow duration and energy evolution characteristics of the flow front after particle collapse in different regimes were systematically analyzed.And we discussed influences of the initial aspect ratio on the collapse flow behavior in different regimes.Finally,parameterization method was used to quantitatively analyze the dependence of flow distance and flow duration on Stokes number and particle fluid density ratio during the transition of particle collapse flow between different characteristic regimes,and the corresponding scaling law was established on this basis.In this paper,a series of numerical simulations were carried out on the collapse flow behavior of particles in the fluid.Based on the existing studies on the collapse flow of dry particles,some new phenomena were observed and some new quantitative results were obtained.With the development of these basic work,on the one hand,we hope to have a deeper understanding of the influence mechanism of the fluid medium on the flow behavior of gravity-driven particle flow from the physical nature.On the other hand,the scaling law based on the established flow distance,flow duration,initial particle height,Stokes number,particle fluid density ratio,etc.,can provide a theoretical basis for the prediction and evaluation of geological hazards with similar flow characteristics in nature.