Discrete Particles Dynamics Of Aeolian Sand Flow Structures

Aeolian sand erosion is the main cause of land desertification and arid landform.The concentration distribution of sand particles related to it is the main influencing factor to study the characteristics of sediment transport,particle collision and aeolian sand flow structure,as well as the most important research content to understand the process of particle collision and the coupling process of aeolian sand two-phase flow.In order to consider the influence of force balance resistance,torque,collision and friction,a new Macroscopic particle model is used to study the movement of sand particles in the airflow.The velocity of sand particles in aeolian processes is an important content in the study of aeolian physics.In order to reflect the change of the concentration and velocity distribution of sand particles in wind-sand movement,this paper used the two-dimensional Euler-Granular model to simulate the flow process of wind-sand from the perspective of multi-phase flow.The model is verified to be accurate by comparing the volume concentration of sand particles with the change of height in the experiment,and the volume fraction of sand phase at different locations showed different distribution states with time flow,which were the start-up stage,development stage and stable stage of aeolian sand flow respectively.With the increase of the frictional wind speed,the volume fraction of sand phase gradually increases in height,while the attenuation rate decreases slowly in the vertical direction,which makes the distribution conform to the exponential attenuation law.On this basis,the movement information of sand particles is analyzed statistically and the velocity distribution of wind-drift sand near the bed surface is obtained after counting the physical quantity of sand particles.The statistical results show that the logarithm of sand volume fraction decays exponentially with the increase of height,and the saturation stratification appears at the same height,and the saturation value decreases with the increase of height.The velocity distribution of sand phase and probability density function of velocity distribution at different time were calculated by counting the velocity information of sand particle with volume fraction greater than 1E-7.According to the results of previous studies,it is found that the macro-particle model can realize the quasi-direct numerical simulation of two-phase coupling of aeolian sand without any additional model.According to the different movement states of aeolian sand flow shown in the cloud map of sand velocity,the conclusions of the vertical distribution of sand concentration are inconsistent.The inherent non-linearity of particle flow system is the main factor that causes the non-uniformity and inconsistency of aeolian sand flow state.The numerical simulation results show that the tracking function of discrete particles in MPM model and the information of particle velocity and position can be used to study the multiphase flow mechanism of aeolian sand movement.Under different sand diameter and wind speed conditions,the concentration,velocity,trajectory,falling Angle and flow field distribution of aeolian sand flow are discussed in this paper.The results show that the landing Angle is greatly affected by random factors such as particle impact and turbulence in the movement of aeolian sand flow.With the increase of wind speed,the probability density distribution of sand particle landing Angle tends to be unified gradually,and the maximum probability density is closer to the theoretical landing Angle of a single sand particle.With the increase of wind speed,the saltation length and maximum saltation height of sand particles also increase gradually,and the movement trajectory gradually tends to be the same.