Numerical Simulation Of The Response Of Dust And Sand Transport To Fluctuating Wind

Dust and sand transport law shows differences between the actual fluctuating or gust wind field and steady wind flow. The response time of sand transport rate to varies with fluctuating parameters of wind field, which leads to the differences of the sand transport rate, sand structure and other physical quantities. And the response degree is of great significance for understanding the actual dust transport law, transport properties, which is benefit of accurately predicting of dust storms. The thesis focus on the response time of sand transport rate to wind speed fluctuations of near-surface saltation sand flow and the dust transport law of high-altitude in the role of the gust. The main works are concluded as following,1. We simulate splashing sand number, sand flow structure (sediment transport rate along the height distribution) and sand transport rate wind-sand flux by using flow typical splash functions. By comparison of results, it can be found that the sand transport rate simulated by the splash function reported by Kok&Renno can be consistent with results measured in wind tunnel, and simulated results can also describe the law of the stratified point along height for sand transport rate.2. Based on the steady-state and unsteady wind-blown sand model, we simulate the response time of sand transport rate to wind speed. It is found that the response time decreases with the increase of flow average wind speed, and increases as the particle size increases in the steady stream; nevertheless, the response time of sudden deceleration of the flow displays instead of the law. The response time in the sinusoidal wind stream decreases with increasing the average wind speed and amplitude, and increases with increasing of the cycle; and the time tends to a constant value at about20s as the cycle increases. In addition, the peak acceleration response time is less than the valley deceleration response time.3. The study of dust and sand transport in gusts wind is carried out through numerical simulation. It is found that the transport height and horizontal distance decreases with the increase of the grain size, and the smaller particles can follow the wind more easily for the dust and sand transport. In case of a mixed particle diameter, the particle size distribution in the air depends on the particle size distribution of initial bed. The average particle diameter is related to the height from the ground. When the height is between10m and20m, mean particle diameter begins to decrease.