Numerical Studies On Sand-dust Storms And Sand Wall Morphology Based On The Modeling Of The Very-large-scale Motions

Based on the field observation of sand-dust storms,an effective numerical model for quantitative simulation of sand-dust storms is established to predict the vertical sand and dust flux in the atmospheric surface layer accurately,which is helpful for accurate forecasting and early warning of sand-dust storms.However,in the current dust storms prediction models,it is impossible to simulate the turbulent transport process of sand and dust,which makes the flux of the underlying surface inaccurate and leads to omission and false positives of sand-dust storms.It has been pointed out that the very-large-scale motions in the atmospheric surface layer are an important and even decisive factor affecting the transport of sand and dust.However,the very-large-scale motions obtained by the numerical simulation of the atmospheric surface layer with high Reynolds number is still very different from the field observation results,which leads to the failure of the simulation of sand-dust storms based on the movement of discrete grains in the high Reynolds number wall turbulence flow,especially the sand nose phenomenon in the front of the sand-dust storms.The "sand nose" shows the transport structure of particles in the sand-dust storms visualized,and the study of the "sand nose" phenomenon is of great significance to understand and characterize the spatial characteristics of sand-dust storms.However,how sand noses come into being and self-sustained in sand-dust storms and how grains move upwards continuously are still unknown.In order to solve these key issues,this dissertation uses a combination of experimental and numerical methods to establishes sand-dust transport model for the first time that can reflect the turbulent transport process of discrete grains in the steady stage of sand-dust storms which also contains the near surface information,and realizes the numerical simulation of sand-dust storms and reproduces the "sand nose" phenomenon.The main innovations and conclusions of this dissertation include:1)Based on measured data of Qingtu Lake observation array(QLOA),the velocity fluctuations of very-large-scale motions existing in the atmospheric surface layer during sand-dust storms were extracted and characterized,and then were introduced into the model so as to embody the “external energy input” characteristic of the atmospheric surface layer during sand-dust storms.2)The connection between the surface flux and the dust flux at different height was established,and the dust vertical flux characterization under different friction wind speed and height was given.3)We argue that sand noses are the results of interactions between streamwise and vertical velocity fluctuations of the very-large-scale motions.The inclination angle of streamwise may be the main reason for the difference of the sand wall morphology.