山区阶梯式河道水流阻力研究

Flow resistance in mountainous streams with stepped channel

山区阶梯式河道是自然界来水来沙和山区大比降河床相互作用所形成的,其水力特性、河道阻力较为复杂。为了深入研究其阻力机理,从河床结构阻水的角度提出阶梯式结构糙率尺度的概念,得到了适用于阶梯式河道跌落水流的形体阻力系数表达式,并由不同来源的阻力分量构成了新的山区阶梯式河道水流总阻力系数公式。新公式结果表明,通过不同类型河段的野外试验数据,表面泥沙、阶梯形状以及漂石产生的阻力系数分量之和与试验测量总阻力系数数据的误差较小。随着雷诺数和阶梯单元尺寸的增加,河床表面的泥沙肤面阻力系数基本不变,阶梯式结构形成的跌落水流过渡到滑行水流,阶梯形体阻力系数逐渐变小,而较大粒径松散漂石产生的水流阻力系数只随着雷诺数的增大而减小。

The configuration of stepped channels in mountainous streams is influenced by the complex hydraulic characteristics,like the inflow,sediments and the larger slope river-bed.To further study its resistance mechanism,a new roughness height formula is derived and applied for the stepped channels by expanding the theory of roughness height of stepped channels configuration from the dimension of the hydraulic radius.The expression of Darcy-Weisbach form factor for the napping flow of the stepped channels is deduced.Thus the formula of total resistance factor is obtained from sources of resistance components.The results of the new formula shows that the error between the total flow resistance factor calculated from the three components and the actual field measured data is small based on the field data of different river sections.With the increase of Reynolds number and the size of step element,the resistance factor of sediment particles on the riverbed surface basically-stabilize at a certain.With the spill flow formed by the stepped riverbed configuration changing into the skimming flow,the resistance coefficient of the body gradually decreases,and the resistance factor of the flow generated by the larger loose boulder descends with the increase of Reynolds number.