Numerical Study On The Effect Of Static Gravel In Saltation Particle Transport

Aeolian particle transport is a common natural phenomenon on Earth.Many physical processes that occur at the Earth’s surface,such as wind-blown sand/dust transport and snow drift,fall under the study of aeolian particle transport.In many aeolian landforms,the surface is generally not a simply granular bed,but is often scattered with static stony deposits of varying size,shape,and nature,such as gravel,cobble,or other hard surface.The bed is thus no longer a homogeneous granular bed,but becomes a complex mixed bed.After decades of development,scholars have gained a good understanding of particle saltation transport on granular beds.In contrast,the current research on saltation transport on mixed bed is still stuck in experimental studies on macroscopic transport laws.The scarcity and lack of depth of numerical simulation work makes it difficult for scholars to obtain complete information on aeolian particle transport processes and its microscopic motions,which greatly limits the understanding and knowledge of saltation transport mechanisms and saltation structures on mixed bed surfaces.In this paper,based on the steady-state model of flow field and Lagrange scheme of particle motion,considered the particle midair collision and two-phase coupling of gas and solid,and at the same time added the collision process between the saltating particles and the mixed bed,the mathematical model of aeolian particle transport on the mixed bed was presented.Through numerical simulation,we investigate the effects of gravel distribution,recovery coefficient and height on the transport laws and stress structure of saltation.The main conclusions are as follows:(1)The presence of gravels has an enhancing effect on both the saltation mass flux and the particle transport rate,causing a decrease in the vertical decay rate of mass flux and an increase in the scalar law of the particle transport rate.(2)The gravel distribution characteristics have less effect on particle transport,and the particle mass fluxes and the particle transport rates are similar for mixed beds with different gravel distribution characteristics under the same coverage conditions.The increase of gravel recovery factor also causes the increase of particle transport rate,but has almost no effect on the scalar law of particle transport rate.(3)An increase in gravel height leads to a decrease in mass flux at lower heights and an increase at higher heights.The effect of gravel height on saltation transport is non-monotonic,enhancing saltation transport over a range of heights.However,too high a height can in turn weaken saltation.(4)The steady-state fluid wall stress on the granular bed is less than the critical stress.However,when gravels are present in the bed,the steady-state fluid wall stress is greater than the critical stress and increases linearly with increasing friction velocity.The total wall shear stress on both types of beds is greater than the initial wall stress,but the total wall stress on the mixed bed is less than the result on the granular bed.