THE INCLUSION OF VORTICAL FLOW STRUCTURES IN ANALYTIC DEPTH-AVERAGED FLOW MODELS OF FLOODING

本文主要研究明渠水流中纵向涡度与平面涡度之间的基本相互作用。平面型涡度是所有雷诺平均N-S方程(RANS)模型中的先验排除项，但已知在大多数漫滩流中都存在。Shiono&Knight分析方法(SKM)是一种模拟涡旋结构影响的解析方法，它模拟了4个关键的主导流动过程，避免了使用三维湍流模型，并在全尺度上应用。尽管SKM方法的价值得到了HR Wallingford最近的工作的证实，但已知原始的F(涡度关联)辅助方程不适用于某些类型的非棱柱型洪泛平原和强蜿蜒河流。一种有希望的方法是使用两层SKM模型，将深度平均过程垂直分割为两个部分，在岸满阶段上方和下方。这允许将横向切片模型放置在另一个切片模型的顶部，并添加水平界面剪切。然后，每个切片中较低的F值代表流向的二次流，而较高的F值既模拟滩地/主槽边界的二次流，又模拟平面形式的涡度。与更复杂的三维湍流模型(LES或RAN)相比，这为这些类型的河道提供了一种简单得多的二维深度平均方法，具有SKM的所有优点。需要开展工作来探索这种新的理论方法，并评估它是否可以转变为实用的电子表格工具，供工程师模拟洪水使用。

This proposal focuses on the fundamental interaction between longitudinal & planform vorticity in open channel flow. Planform vorticity is a priori excluded from all Reynolds averaged Navier-Stokes (RANS) equation models, but is known to be present in most overbank flows . The Shiono & Knight method of analysis (SKM) is an analytic approach to modelling the influence of vortical structures, mimics 4 key dominant flow processes, avoids the use of 3-D turbulence models and applies at full scale.Despite the value of the SKM approach being confirmed by recent work at HR Wallingford, the original ancillary equations for F (vorticity linked) are known to be inadequate for certain types of non-prismatic floodplains and strongly meandering rivers. One promising approach is to use a two-layer SKM model, splitting vertically the depth-averaging process into two parts, above and below the bankfull stage. This allows a laterally sliced model to be placed on top of another sliced model, with horizontal inter-facial shear added. The lower F values in each slice then represent the streamwise secondary flows, and the upper ones mimic both secondary flows at floodplain/main channel boundaries and plan form vorticity. This produces a much simpler 2-D depth-averaged approach for these types of channel, with all the advantages of SKM, over more complex 3-D turbulence models (LES or RANS). Work is needed to explore this novel theoretical approach, and to assess whether it can be turned into practical spreadsheet tools for use by engineers modelling floods.