Some Investigations Into Sand-dust Emission In Wind Tunnel

Sand-dust emission is a key surface process of forming dust storms, dust aerosols is an important part of atmospheric aerosols. In the dust storms areas, sand burial and blocking the road have often occurred, visibility drops to increase the probability of traffic accidents, and so on, which endangers human life and socio-economic. The atmospheric dust aerosols suspended in the atmosphere has important influence on the global climate and ecosystems.In the present experimental researches, the gradient method was employed to measure the dust emission rate, which was derived from the concentration gradient of dust in the air measured, on the assumption that dust eddy diffusivity was approximated to eddy viscosity. The measured results became susceptible to dust from far away, accuracy is no guarantee. So far there is no effective method to directly measure sand emission rate. Motivated by these problems of dust emission, dust emission rates and sand liftoff rates are directly measured by wind tunnel experiments using the contactless opticalinstrument--Particle Image Velocimetry (PIV). Wind tunnel experiments were carried out on characteristic physical quantities in the mechanism of sand emission. The main topics are as follows:By PIV in wind tunnel, the directly measured results of sand liftoff rate are obtained. An empirical equation of sand emission rate against wind friction velocity is proposed. The measurement results of the rate of sand liftoff number are obtained, and further the reliability of this parameter is improved. Our findings suggest that the result considering electrostatic force is closer to the true value than that without considering electrostatic force, in the numerical simulation of Aeolian sand transport. Through analyzing the distribution of the grain size of lifting off sand, it is found that strong wind redounds to coarse sand transport, and weak wind is more conducive to sift the bed sand.Abandoned farmland around desert is one of the important dust sources in our country. By PIV, some investigations into dust emission rate and the grain size of dust emitting from the surface for this type of soil, are carried out in wind tunnel. The methods of studying dust emission are expanded, which makes the direct measurement of dust emission rate come true. The relationship between dust emission rate and wind friction velocity is obtained. Through analyzing the grain size of dust emitting from the surface and the impact velocity and grain size of saltating particle, some factors that influence the average grain size of dust emitting are discussed.Sandy loam surface is one of the typical dust emission sources. Using Aerosol Spectrometer the local dust concentration is measured, then the gradient method is employed to calculate dust emission rate. The results show that the dust emission rate scales with u*4to u*5. Sandblasting efficiency which indicates the efficiency of the release of dust aerosols due to saltation bombardment, is an important factor for dust emission process. Analyzing the results of this paper combined with previous researches (Shao et al.,1993), the findings suggest the decisive factor whether or sandblasting efficiency changes with friction velocity.