Influences of coarse bank roughness on flow within a sharply curved river bend
Influences of coarse bank roughness on flow within a sharply curved river bend
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粗岸粗糙度对急弯河湾内流量的影响
DOI：
10.1016/0169-555x(95)00007-r
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发表时间：
1995
期刊：
影响因子：
3.9
通讯作者：
D. Furbish
中科院分区：
文献类型：
--
作者：
S. D. Thorne;D. Furbish
进行了一项试验，以评估粗糙度对奥克拉瓦哈河急弯内水流的影响。奥克拉瓦哈河位于佛罗里达州北部，是一条沙质河流。这涉及到在外岸有天然植被粗糙时获得系统的流速和水面地形测量，以及在移除植被并沿着外岸建造光滑的墙后获得一套相同的测量结果。结果表明，岸边植被粗糙度通过对横向边界层的影响，系统地影响了流场，特别是二次流强度和高速核的位置。粗糙度本质上产生了一种回水效应，阻止了向外的地表水流接近外滩。这抑制了外滩的超高，从而削弱了向内的横向压力梯度和二次流。水流被引导向下游方向，高流速的核心几乎集中在渠道中。在没有植被粗糙度的情况下，向外的地表水流更直接地接近外滩(在弯道中更早)，外滩超高增强，横向压力梯度和二次流增强。高速核向外滩移动，震级增大。此外，在存在粗糙度的情况下，高速核心最接近外岸的流向位置从其最接近的位置向下游移动。原则上，这应该有助于不对称的弯曲迁移，而在存在粗糙度的情况下的迁移应该与弯曲曲率几乎同步，从而使弯曲在幅度上增长，尽管增长速度较慢，而且不对称程度较低。
An experiment was performed to assess the influence of coarse bank roughness on flow within a sharply curved bend of the Ocklawaha Creek, a sand-bedded stream in northern Florida. This involved obtaining systematic measurements of flow velocity and water-surface topography when the outer bank was rough with natural vegetation, and obtaining an identical set of measurements after removing the vegetation and constructing a smooth wall along the outer bank. Results suggest that the roughness from bank vegetation systematically influences the flow field, particularly the secondary current strength and the position of the high-velocity core, because of its effect on the transverse boundary layer. The roughness essentially produces a backwater effect that inhibits outwardly directed surface flow from closely approaching the outer bank. This suppresses super-elevation on the outside bank and, therefore, weakens the inwardly directed transverse pressure gradient and secondary current. The flow is steered in a downstream direction, and the core of high velocity is nearly centered in the channel. In absence of roughness from vegetation, outwardly directed surface flows approach the outer bank more directly (and earlier in the bend), superelevation on the outside bank is enhanced, and the transverse pressure gradient and secondary current are strengthened. The core of high velocity is displaced toward the outer bank, and its magnitude is increased. Moreover, the streamwise position where the high-velocity core is closest to the outer bank shifts downstream from its position of closest approach in the presence of roughness. This, in principle, should contribute to asymmetrical bend migration, whereas migration in presence of roughness should be nearly in phase with bend curvature such that bends grow in amplitude, albeit slower, and with less asymmetry.