Numerical Simulation Of Wind-Blown Sand Saltation In Random Wind Field

The main model of aeolian sand is saltation. Saltation can eject dust aerosols into the atmosphere, create sand dunes, and erode geological features. In the study of sand movement, generally, we only consider the mean wind speed, ignoring the impact of fluctuating wind speed on particle motion. However, ignoring the fluctuating part of the moving particles will directly affect the results of the quantitative study of particle motion. Therefore, the research of fluctuating wind speed’s effect on saltation is very important. This thesis is about the numerical simulation of saltation under wind speed fluctuating in the atmospheric boundary layer to provide some references for experimental research and theoretical analysis. In the study, saltation of the single size bed and mixed size bed is studied. The main contents are as follows:1. A specific description of the mathematical model of stochastic wind field is put forward at first. Then the kinematic simulation gives specific random Fourier fluctuating wind field equations and generates specific random fluctuations. We use the random Fourier series to generate the independent vector component (such as frequency, wave number, etc.) in the fluctuating wind field. The parameters to the control of random fluctuations in this study, such as frequency, takes the mean of0and standard deviation of a Gaussian random distribution, and wave number takes the mean for0and a standard deviation of0.5Gaussian random distribution.2. Under the random fluctuating wind field, we simulate particle motion of single size and mixed size bed. For the single size bed, we get the relationship between wind speed and the friction velocity and Fourier nodes, and determine the value of the number of nodes. After the number of nodes is determined, we conduct a comparison of the numerical fluctuating wind speed and the experimental fluctuating wind speed. The results show well consistency. We simulate the sediment transport rate with the variation of the friction velocity. And the results are compared with the experimental values and the classical formula. The results of our simulation are better. Vertical mass flux and horizontal mass flux of particles and the change of sand particle size distribution are obtained too.3. For mixed particle size bed, we obtain the number of nodes firstly. Then we compare the experimental fluctuating wind speed and the simulation fluctuating wind speed. The results is identical with that of the single size bed. We also simulate the vertical mass flux and the horizontal mass flux of particles with the variation of the friction velocity. Compared with the experimental values, both of them are in good agreements. For mixing size bed, we study the relationship between the sand particles and the friction velocity. The results indicate that the distribution of the particles has a close relationship with the friction velocity when saltation reaches the steady state.4. Considering the fluctuating wind field, the numerical simulation and experimental results are in good agreements. For both the single size bed and mixed size bed, simulation results and experimental values are consistent, which tells that the fluctuating effect on the actual particle movement can not be ignored.