基于滩槽间非恒定质量输移的溃坝水流结构及洪水波演进规律研究

Studies on the issue of a dam-break flood have been occupying considerable investigators since 19th century due to both the catastrophe resulting from a dam failure and the complexity of flow characteristics. It is also a strict rule in Reservoir Flood Protection and Rescue Contingency Plans Preparation Guidelines that the propagation of a flood wave caused by a dam collapse should be determined as a base for other analyses. A large number of achievements show that the cross-sectional shape of river is one of the primary factors influencing the wave propagation. Compared to a single channel, deeply understanding the characteristics of the dam-break flood routing in a compound channel may be of more practical value in these aspects of determining the flood affecting area, escape route, temporary residence, etc, because the human activities in the vicinity of floodplains are often dense. The key of this project contains the spatial and temporal distribution of flow structure in the main channel and floodplains in the rising and recession courses of a flood, the formulae for quantitatively describing the transient mass transport resulting from the flow lateral movement between the main channel and floodplains, the effect of the flow lateral movement on the momentum transfer in the interacting region between the main channel and floodplains, the methods for predicting the apparent shear stress in the interface, the momentum transfer coefficient and the kinetic energy loss under the condition of unsteady flow, the numerical model for simultaneously routing the floods in both main channel and floodplains. Investigations on a dam-break flood involving the transient mass transport between the main channel and floodplains are helpful to seek further insight into the unsteady-flow structure in a compound channel and the resulting impact on the flood wave propagation; and it would be profoundly important for the basic theory of the mechanics of river dynamics.

由于溃坝洪水造成的巨大危害及其水流运动的复杂性，自十九世纪以来，对其展开的研究从未停止。《水库防洪抢险应急预案编制导则》中也明确要求对水库大坝作溃决洪水计算分析。研究表明，溃坝洪水传播极大程度上受着河道断面形态的影响。与单一河槽相比，由于滩地附近常伴有密集的人类活动，因此深入理解与掌握复式河槽洪水波演进规律在制定洪水影响区域范围、转移路线及安置点等方面更具实用价值。项目重点研究洪水涨落过程中主槽与滩地流场内部结构的时空分布规律，可定量描述滩槽间非恒定质量输移行为的数学模型，滩槽间水流横向运动对交互区动量交换的影响机制，非恒定流条件下表观剪切力、横向动量输运、能量损失的计算方法，滩槽洪水同时演进数值模型。基于滩槽间非恒定质量输移的溃坝洪水问题研究，有助于深入认识非恒定流条件下复式河槽水流结构及其对洪水波演进规律的影响，在河流动力学基础理论方面具有重要的学术意义。

由于溃坝洪水造成的巨大危害及其水流运动的复杂性，自十九世纪以来，对其展开的研究从未停止。《水库防洪抢险应急预案编制导则》中也明确要求对水库大坝作溃决洪水计算分析。研究表明，溃坝洪水传播极大程度上受着河道断面形态的影响。与单一河槽相比，由于滩地附近常伴有密集的人类活动，复式河槽溃坝洪水波演进情况在制定洪水影响区域范围、转移路线及安置点等方面更具实用价值。项目重点研究了洪水涨落过程中滩槽间水流横向运动引起的非恒定质量输移行为，滩槽间水流横向运动对交互区动量交换的激增效应，非恒定流条件下表观剪切力、横向动量输运、能量损失的计算方法，滩地植被作用下溃坝水流结构的复杂响应与相应水流阻力变化规律，滩槽洪水同时演进数值模型。研究表明，在滩地宽度有限情况下，主槽漫溢水体在撞到滩地侧壁后会在侧壁区域形成雍水区，该区水体会横向流向主槽并影响主槽水体后续的漫溢过程。滩地初始无水时滩槽间的波前演进速度差异较大，但滩地初始有水时，流速差异较小。分别在滩槽内建立控制方程，并通过在连续方程中引入侧向流量，在动量方程中引入表观剪切力以及侧向质量交换引起的动量传递将原始的圣维南方程进行了改进，使得新数学模型能够考虑洪水作用下滩槽间的动质量输移特性。滩槽水体的动质量输移显著影响了水流结构，流动中出现了包括滩地水深平均速度大于主槽、滩地侧壁区出现河床剪切力峰值、滩地河床剪切力大于主槽等与恒定流情况下完全不同的流动现象，在实际防洪工作应重点关注这些特征。滩槽间主要的动质量输移都发生在洪水涨退的前半段时间，与现有计算滩槽动质量交换的公式进行对比后发现，目前的计算方法存在较大限制，还无法完整准确的描述整个滩槽动质量交换过程，在实际应用中应谨慎。基于滩槽间非恒定质量输移的溃坝洪水问题研究，有助于深入认识非恒定流条件下复式河槽水流结构及其对洪水波演进规律的影响，在河流动力学基础理论方面具有重要的学术意义。