Research Of The Characteristics Of Flow Field In A Porous Medium Forest Model

The problem of desertification is more and more serious and has an important effect on human production and life. The intuitive expression of wind erosion and sandstorm is windblown sand movement. The vegetation can not only decrease the wind speed effectively and reduce the surface shear stress, but also resist parts of particle transport. On the other hand, the vegetation can fix the soil to protect the soil from being blown away, thus reducing the intensity of winblown sand movement and wind erosion. Therefore, it is necessary to research the characteristics of the flow field near and in vegetation so as to provide some support for windproof and desert controls. Commercial software FLUENT is used in this paper to study the characteristics of flow field when the wind and dust goes through the forest.1. First, the basic theory of porous media model was introduced. The space-average method was used to transform the time-averaged N-S equations to obtain the control equation of flow field. The parameters of calculation model were given. Then the basic theory of the euler two-phase model was derived, at the same time, the parameters of the governing equations were given.2. The forest is considered as a porous media region. Numerical simulation of the characteristics of the flow field through the forest was conducted, and the results were compared with the results of the previous experiments and numerical simulation and showed good agreement. So the forest porous media model was verified. Resistance effect to wind of forest is obvious: in the forest canopy position, wind speed along the flow direction of 10 m length reduced by 10.48%, wind speed along the flow direction of 50 m length reduced by 27.21%. When wind entered the forest, turbulence intensity below the height of forest increased first, and then decreases slowly, which reached maximum in half of the forest height. Turbulence intensity variation trend is decreasing rapidly above the forest.3. Combined with the basic theory of porous media model and euler two-phase model, the solid particles was considered as a continuous fluid, numerical simulated the flow field characteristics when the dust goes through the forest. The distribution of the volume concentration and the mass flux of dust were studied. The results show that the dust volume concentration decrease rapidly within a short distance near the ground, and then the dust volume concentration decrease slowly as the height increase. The dust volume concentration decrease rapidly in the forest, and it has an little increase at the canopy of the forest,and it decreases above the forest.The mass flux decreases rapidly under the forest, then increases rapidly above the forest and it increases to the maximum at two times the height of the forest, at last it gradually reduced to 0. At the same height, the larger the particle size, the larger the volume concentration and the mass flux, which shows that the forest has better resisting effect for the large particle size.