Visualization For Sand Saltating Motion In The Shelter Region Of Wind Fence

Wind erosion covers the detachment, transportation, and redeposition of solid particles such as soil, sand, and other particles by wind in the natural environment. This wind-blown transport phenomenon can be considered as a special case of gas-solid two-phase flows. Wind erosion is a major cause of soil degradation, desertification, and sandstorms which result in serious environment problems. To protect the environment from wind erosion of drifting sand, the porous wind fence, termed an artificial barrier, has been widely used in coastal, arid, and desert areas. This study investigated the shelter effect of a porous wind fence on saltating sand in a simulated atmospheric boundary (ABL). Both the flow structure and saltating sand motion around the fence were visualized so as to reveal the mechanism of abating sand transport from wind fence.This study provided a flow visualization test in the region around the wind fence model by using particle image velocimetry (PIV) system. The mean velocity, vorticity, turbulence intensity, turbulent kinetic energy, and Reynolds stress of the flow were measured. In this test, it showed the influence of wind fence on kinetic energy intensity and turbulence of the incoming flow.In the following, a high-speed digital camera was used to capture consecutive images of saltating sand particles around the fence, and then, the particle tracking velocimetry (PTV) method was employed to quantify the saltation parameters. A particle identification algorithm for filtering was progressed to eliminate the noise of raw images. As a result, the mean velocity, volume concentration, mass flux, reduction rate, and kinetic energy of saltating sand were extracted. These parameters were analyzed and compared with the case of no fence to reveal the effect on wind-blown sand transport structure. It indicated that the sand mass flux in the windward region decreases exponentially with the vertical height from the ground similar to the case of no fence.A further processing algorithm was employed to reconstruct the trajectories of particles saltating behind the fence. With the obtained experimental data, a statistical analysis was performed to extract the probability density distribution of sand-bed impact parameter, such as incident velocities, incident angles, and momentum and energy restitution coefficients. These collision parameters were analyzed and compared with the case of no fence to evaluate the shelter effect of wind fence on sand-bed impact process. The incident angles of the two sand samples are significantly increased in the near wake region behind the fence. The saltating particles lose a large portion of their energy during the collision process in the wake region. These results illustrate that the porous wind fence effectively abates the further evolution of saltating sand particles.The porous fence was found to be effective in reducing the kinetic energy of saltating sand and in increasing the proportion of energy loss during the collision process, thus abating further evolution of the saltating sand. In addition, this study effectively provided more accuracy than previous corresponding researches, thus improved the visualization of sand saltation method The present experimental results are useful in understanding sand transport phenomena through a porous fence and in evaluating the shelter effect of the wind fence.