Study On The Non-steady-state Characteristics Of Vertical, Flow Direction And Bed Erosion Of Wind-blown Sand Migratio

As one of the most common physical phenomena on the earth surface,aeolian sand transport is a classical subject of aeolian physics.Besides of making various wind erosion landscapes,the transport is the source of many natural disasters such as wind blowing sand and dust,and even sandstorms,which can do great damage to human life and property.The study of aeolian sand transport has great significance for theoretical research and practical application,so it has been attracted much more attention from the researchers of physics,geography and environment.In this paper,the unsteady characteristic of aeolian sand transport has been investigated along the vertical direction,the stream direction and the local spot on the sand bed surface by means of field observation,theoretical analysis and wind tunnel experiment.The results are represented as follow:1.The closer to the bed surface,the less energy the gust contains.Considering the intensity ofthe interaction between unsteady wind and sand along the vertical direction,two characteristic heights H= 300 mm and H= 800 mm are determined.Then the space above the bed surface can be divided into three zones: active zone,subactive zone and inertia zone.The para-momentum exchange theory between the two phases is proposed based on the similarity of the distribution of gust velocity at different heights and sand particle size in bed surface.2.By introducing the concept of the fluid initiation region,the revised aeolian transport model for the relaxation process is proposed here.The revised model has good applicability and matches well with the experimental results.Based on the theoretical analysis of the damping oscillation model,saturation length has been given a new physical definition.The calculation for the experimental data shows that the saturation length is a fixed value about 1 m.3.The aeolian erosion experiments on the sand bed surfaces under unsteady sinusoidal wind blowing are first performed in the wind tunnel.The effects of wind speed frequency and amplitude variation on the aeolian erosion rates are measured under the conditions of two types of wind-sand migration driven by the sinusoidal varying wind,namely threshold migration and continuous migration.It can be concluded from the experimental results that the erosion rate would vary with the changing of frequency and amplitude of the unsteady sinusoidal wind.the erosion rate is not certain to response the unsteady sinusoidal wind with positive feedback.Only when the gustiness degree can offset the intermittent of sand movement,the erosion rate makes positive feedback to the sinusoidal variation of wind velocity.Compared with the corresponding steady incoming flow experiment with the same value of time-averaged wind velocity,the erosion rate in unsteady aeolian sand transport process can increase by up to 17% due to the changing of amplitude of the unsteady sinusoidal wind.Meanwhile,the frequency variation of the unsteady sinusoidal wind can make the erosion rate increase by up to 18%.Based on the research of the unsteady characteristics of aeolian sand transport Within different spatial dimensions,some achievements have been proposed like the paramomentum exchange theory between the wind and sand phases,the revised relaxation model of the transportation and the conclusion about the effect of sinusoidal wind velocity changing on the erosion rate of the sand bed surface.The works in the paper could be useful for the theoretical research of unsteady aeolian sand transport and its practical application.