明渠紊流中泥沙颗粒输移的大涡模拟研究

Large eddy simulation of sediment particles transport in turbulent open channel flow

应用大涡模拟、浸入边界法和有限元—离散元联合法,数值模拟了明渠紊流中2-3层紧密堆积的离散泥沙颗粒的起动和输移,计算了不同输沙强度下,泥沙颗粒运动和受力的统计特征、泥沙浓度、泥沙体积通量密度和输沙率,以及流场的速度剖面和紊动强度等。研究发现:泥沙颗粒的起动和输移对紊流的统计特征有明显影响;主流区的泥沙浓度和体积通量密度随高度的增加呈指数下降;颗粒所受平均升力与输沙强度关系不明显,其最大值约为0.6倍的颗粒浮容重;升力的紊动强度随输沙强度等增大而增大,且数值远大于其平均值,紊流结构引起的脉动升力是泥沙颗粒起动的主要原因。

The entrainment and transport of 2 - 3 layers of densely-packed discrete sediment particles in a tur- bulent open channel flow were investigated by combining three numerical technologies, i.e. the large eddy simulation, the combined finite-discrete element method and the immersed boundary method. The hydrody- namic forces on sediment particles with different transport stages, together with the particle velocities, sedi- ment concentration, volumetric flux density, volumetric sediment flux, flow velocity profiles and turbulence in- tensities, were investigated. It was found that the entrainment and transport of sediment particles have strong effects on flow velocity profiles and turbulence intensities. The sediment concentration and volumetric flux den- sity decrease exponentially with increasing height in the outer flow region. The mean hydrodynamic forces on sediment particles show less dependency on the transport stage and attain a maximum of 0.6 times of sub- merged weight of the particles for all three cases with different Shields numbers. However, the fluctuations of the lift force increase with increasing transport stages and their values are much larger than the mean values. Thus, the fluctuating lift force caused by the turbulence coherent structures is the real reason for the upward motion of the sediment particles.