分汊河道近底水流特性试验研究

Experimental Study on the Characteristics of Near-Bottom Flow in Bifurcated Channel

近底水流结构是影响泥沙起动、床面变形以及航道整治建筑物稳定性的直接因素。以长江中游武汉天兴洲段这一典型分汊河道为原型,开展物理概化模型试验,通过对比纵横向测点的流速差异,分析分汊河道近底流速分布特性以及近底水流脉动变化规律。结果表明:河床地形对近底水流时均流速有一定的影响,分流区内时均流速沿横向分布较为均匀,而汊道段时均流速沿横向和纵向上分布均有波动,总体上河床高的地方流速大,且与测点处的水深呈负相关;脉动强度与该点处时均流速之比称为相对脉动强度。江心洲逆坡段的滩槽交界区域水流结构复杂,相对脉动强度大,在平直的滩顶段则是滩面处的相对脉动强度最大。

The structure of near-bottom flow is a direct factor that affects the sediment movement,the deformation of bed surface,and the stability of waterway regulation buildings,for which the Tianxingzhou section,a typical bifurcated channel,of the middle reaches of the Yangtze River in Wuhan was anatomized.A physical generalization model experiment was carried out.The near-bottom flow velocity distribution and its fluctuation mechanism was studied using data collected in different locations.Results show that the riverbed topography have a certain influence on the average near-bottom velocity,and the traverse distribution of time-averaged flow velocity in the distributary region is relatively uniform.However,the distribution of the time-averaged flow velocity in the inlet area fluctuate along the transverse and longitudinal directions.Generally,the flow velocity is higher at the place with higher riverbed and it has a negative correlation with the water depth.The ratio of the fluctuation intensity to the time-averaged velocity at the measurement point is termed the relative fluctuation intensity.The fluctuation intensity in beach-channel junction area at reverse slope is relatively large because of the complex flow structure.In the flat beach top section,the maximum relative fluctuation intensity occurs on the beach surface along the transverse.