Study On The Movement Of Non-Spherical Coarse Particle Using Large Eddy Simulation And Discrete Element Method

Bed-load transport is vital important for port construction,river channel erosion control and shoreline erosion prediction.There are many factors affecting the bed-load transport,such as particle sizes,particle gradation,particle shape,etc.For simplifying sediment transport,the particles are always simplified into 2D sphere,however,the natural sediment shape is more complicated,the force coefficient of nature sediment is quite different from the sphere,and the 3D asymmetry of natural sediment is neglected by simplifying the particle into 2D sphere.At present,there are still insufficient numerical simulation studies on non-spherical sediment particles.For this work,the non-spherical sediment particle model is established by the large eddy numerical simulation combined with the discrete element method.By simplifying the influencing factors,the effects of fluid on single-particle(particle sedimentation)and solid-to-solid interaction(sludge angle of repose study)were studied firstly.On this basis,the influence of shape factors on the initiation of coarse-grained sediment and all bed-load transport were further studied.the results show that:For the sedimentation of sediment: with the increase of Reynolds number,the nonspherical sediment particles develop into the unstable state faster than the sphere.The CSF number mainly affects the sedimentation velocity.Under the small Reynolds number condition,there is a linear growth relationship with the number of CSF;however,the trajectory of sediments is related to particle classification,and the CSF number is insufficient to describe the trajectory of sediments.In terms of repose angle: on one hand,as the CSF decreases,the compactness of particle accumulation decreases first and then increases;on the other hand,the density of particle accumulation decreases with the increase of the bottom slope,and the bottom slope affect the compactness of particle accumulation too.The sensitivity of the steady velocity to the slope decreases as the number of CSF decreases;the non-spherical particle flow has strong 3D characteristics,there is a significant lack of simulation through average equations.For initial motion of sediment in a laminar flow state: rolling is the only motion mode for sphere,while the motion mode of non-spherical particle is rolling or combined sliding.The use of critical force to study the initial motion of particle under laminar flow also has limitations.It is necessary to introduce the concept of impulse.In general,disk-shape need the largest.energy for entrainment.For the bed-load transport: the particle motion is similar to the wave motion under the large Reynolds number condition.And the non-spherical shape parameters also affect the particle velocity and the motion height probability distribution.