中文摘要：

用实验和计算模拟的方法研究了颗粒流中的颗粒速度与颗粒流特性的关系．实验研究发现当人口流量固定时，在出口上方高速运动的颗粒会使颗粒流由稀疏流向密集流转变的临界出口尺寸变小．当颗粒流转变为密集流后，颗粒速度的作用被出口上方的颗粒堆积区所消耗，最终变得与颗粒速度无关．二维分子动力学模拟计算得到了与实验相同的结论．通过二维分子动力学模拟计算，还给出了不同颗粒速度下体系的密度和速率在空间的分布图．这些分布图显示随着颗粒到达出口上方的瞬间速度的不同，颗粒堆积区的密度和高度均会改变，并最终导致颗粒流流动状态的改变．

英文摘要：

The effect of granule velocity on the dilute-dense flow transition in granular system is studied both experimentally and by numerical simulations. Our experiments show that high granule velocity above the exit results in a decrease of critical exit size in dilute-dense flow transition if the inflow rate is fixed. When the granular flow becomes the dense flow, the effect of the granule velocity is counteracted by a high density region above the exit, and the outflow rate is almost irrelative with the granule velocity. Similar results are also obtained by molecular dynamics simulations for corresponding two-dimensional systems. With simulation calculations, the space distributions of the density and speed are also obtained. The distributions show that the density and the thickness of the granule accumulation above the exit vary with the incoming granule velocity, and the variation plays a key role in determining the final granular flow state.