Scour evolution downstream of grade-control structures under unsteady flows: A theoretical analysis

IF 2.4 3区 环境科学与生态学 Q2 ENGINEERING, CIVIL Journal of Hydro-environment Research Pub Date : 2023-05-01 DOI:10.1016/j.jher.2023.04.001
Jessica Di Nardi , Michele Palermo , Fabián A. Bombardelli , Stefano Pagliara
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Abstract

River restoration projects often make use of grade-control structures in order to prevent channel degradation, improve their ecological resources, and regulate floods. The time evolution of localized scour that can occur downstream of grade-control structures represents a crucial component in the design of those projects. This is because erosion processes may undermine the stability of hydraulic structures and compromise their effectiveness. Although localized scour has been widely investigated (mostly via laboratory models), there is significant scatter in results produced by the large number of obtained empirical equations. Consequently, there is a need for more general tools based on theoretical approaches that might overcome the limits of ad-hoc, experimental methods. In particular, a model based on the application of the Phenomenological Theory of Turbulence (PTT) has been recently developed by the last three authors to predict scour-depth evolution under steady flows. Nevertheless, in practical applications, scour phenomena usually occur during floods characterized by variable flow discharges. In this paper, for the first time to the authors’ knowledge, a detailed analysis of the basic assumptions of the PTT-evolution model allowed us to assess their validity for scour processes at different grade-control structures under unsteady (time-dependent) flows. By re-analyzing the dynamics of the scour evolution under unsteady flow conditions, we corroborate its consistency with the steady counterpart and with jet-driven scour problems, evincing that a homothetical evolution of the scour hole occurs during the developed phase. Finally, we provide a confirmation of the general validity of the theoretical approach presented herein. We show that it can be successfully applied to a large range of structure configurations and hydraulic conditions, without any significant modification. This last result is particularly important, since it paves the way to a unique, first-principles-based tool that can be helpful to design hydraulic structures.

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非定常流场下控级结构下游冲刷演化的理论分析
河流修复工程通常利用等级控制结构来防止河道退化,改善其生态资源,并调节洪水。可能发生在坡度控制结构下游的局部冲刷的时间演变是这些项目设计中的一个关键组成部分。这是因为侵蚀过程可能会破坏水工结构的稳定性并损害其有效性。尽管已经对局部冲刷进行了广泛的研究(主要是通过实验室模型),但所获得的大量经验方程产生的结果存在显著的分散性。因此,需要基于理论方法的更通用的工具,这些工具可能会克服特设实验方法的限制。特别是,最近三位作者开发了一个基于湍流现象学理论(PTT)应用的模型,用于预测稳定流下的冲刷深度演变。然而,在实际应用中,冲刷现象通常发生在以可变流量为特征的洪水期间。在本文中,据作者所知,首次对PTT演变模型的基本假设进行了详细分析,使我们能够评估它们在非定常(时间相关)流量下对不同坡度控制结构冲刷过程的有效性。通过重新分析非恒定流条件下冲刷演变的动力学,我们证实了其与稳定冲刷和射流驱动冲刷问题的一致性,表明冲刷坑在发育阶段发生了相似的演变。最后,我们证实了本文提出的理论方法的普遍有效性。我们表明,它可以成功地应用于各种结构配置和水力条件,而无需任何重大修改。最后一个结果尤其重要,因为它为一种独特的、基于第一原理的工具铺平了道路,这种工具有助于设计水工结构。
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来源期刊
Journal of Hydro-environment Research
Journal of Hydro-environment Research ENGINEERING, CIVIL-ENVIRONMENTAL SCIENCES
CiteScore
5.80
自引率
0.00%
发文量
34
审稿时长
98 days
期刊介绍: The journal aims to provide an international platform for the dissemination of research and engineering applications related to water and hydraulic problems in the Asia-Pacific region. The journal provides a wide distribution at affordable subscription rate, as well as a rapid reviewing and publication time. The journal particularly encourages papers from young researchers. Papers that require extensive language editing, qualify for editorial assistance with American Journal Experts, a Language Editing Company that Elsevier recommends. Authors submitting to this journal are entitled to a 10% discount.
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