Simulation Of Wind-blown Flow And Research Of Spatial Distribution Of Dust Based On Multi-scale Turbulent Motion Reconstruction

Turbulent motion in the atmospheric surface layer has strong pulsation.Recent studies have shown that there are large-scale and very-large-scale turbulent coherent structures in the atmospheric surface layer,which have an important contribution to the turbulent kinetic energy and Reynolds stress of the atmospheric surface layer.Moreover,the turbulent motion in the atmospheric surface layer has an important influence on the transport of heat,momentum and matter.However,the existing wind-blown flow model and the dust transport model cannot reflect the turbulent motion in the actual atmospheric surface layer well.To this end,this dissertation has improved the existing wind-blown flow and dust transport models based on field observation data,that is,introducing turbulence in the atmospheric surface layer into the two model.The specific ideas are as follows: 1)Based on the characterization of turbulent motion at different scales(the characterization parameters are determined according to field observation data),streamwise and vertical wind speed in the atmospheric surface layer are predicted to construct a two-dimensional wind speed pulsation field;2)The two-dimensional wind pulsation field is introduced into the saltation,which is one of the four subprocesses in wind-blown flow model,to simulate wind-blown flow considering turbulence;3)The two-dimensional wind pulsation field is introduced into the dust particle motion equation in the dust transport model to predict the dust transport considering turbulence.The improved models were used to study the statistical properties of wind-blown flow and the properties of dust transport.The main results obtained are as follows: 1)The model prediction results are in good agreement with the existing experimental results,which indicates that the improved models are effective;2)The mean of these physical quantities,such as sediment transport rate of unit width,average jump height,average jump length,consider a difference over 20% before and after considering turbulence.Moreover,the standard deviation of these physical quantities,such as,sediment transport rate of unit width,average jump height,average jump length,sand jump speed,lift-off speed,splash speed,rebound speed,lift-off angle,and the number of lift-off sands,consider obvious difference before and after considering turbulence,and the relative error of some values even exceeds 100%.These results indicate that in the simulation of the wind-blown flow model,the effect of turbulence on it needs to be considered,that is,the effect of turbulence on the wind-blown flow needs to be introduced in the framework of aeolian progress;3)The effect of large-scale turbulent motion in the flow direction and vertical direction on the main statistic of wind-blown flow cannot be ignored.For example,when the large-scale turbulent pulsations in vertical and flow directions are not considered,the relative error between the statistics of the wind-blown flow and that when considering the full-scale can reach 92%.This result indicates that in the simulation of wind-blown flow,only considering the large-scale turbulent pulsation in flow and vertical direction can achieve a general accurate prediction of the properties of wind-blown flow.4)The effect of the turbulent structure of the flow direction on the predicted dimensionless height profile of the dust average concentration is not obvious,but the vertical low-frequency pulsating wind speed plays an important role in the upward transport of dust;5)Whether it is 10 micron dust particles or 40 micron dust particles,the relationship of vertical velocity of the dust particles and the vertical pulsation of the flow field are positive.That is,the dust particles have good followability.Particles larger than 20?m are difficult to transport to the upper part of the atmospheric surface layer;6)The characterization formulas of the average jump length and the saltating sand velocity,which are associated with the movement of the saltating sand,the characterization formulas of the lift-off speed and the lift-off angle associated with the sand-bed collision process,the characterization formula of the sediment transport rate,and the formula of the dimensionless concentration height profile are all given as a function of wind speed and particle size.These formulas will provide an important basis for the implementation and optimization of sand control projects.