AI 中文总结
研究基岩河流中瀑布流行为，利用涡分辨计算流体动力学模型及大涡模拟，发现不同流量下产生瀑布流的最佳收缩率，高流量时收缩可放大瀑布效应、增加速度方差和脉动频率，强调改进基岩下切模型以超越简化稳态流假设。
AI 中文摘要
基岩束缚河道形态中的非均匀流动动力学在地貌演化中起关键作用，因其是基岩活跃下切的河段。实地观测表明，瀑布流在基岩束缚的收缩-水潭-拓宽（CPW）河道形态中驱动局部下切，产生高剪应力促进泥沙输移。以往研究依赖粗尺度实地观测和劳动密集型实验室实验。本文利用涡分辨计算流体动力学模型，基于侧向河道收缩诱发瀑布流的实验证据研究瀑布流行为。通过实验室尺度水流的大涡模拟发现，低流量条件下产生瀑布流的最佳收缩率约为35%，高流量时增至50%，高流量时收缩进一步放大瀑布效应，增加收缩还导致速度方差增大和瀑布流脉动更频繁，这些都可能增强下切潜力。研究强调需改进基岩下切模型，超越支撑多数地貌演化模型的简化稳态流假设。
英文摘要
Non-uniform flow dynamics in bedrock-bound channel morphologies play a critical role in landscape evolution because these reaches are locations along river long profiles where active bedrock incision occurs. Field observations indicate that plunging flows, characterized by velocity inversions within bedrock-bound constriction-pool-widening (CPW) channel morphologies, drive incision at the local scale. These flows generate high shear stresses that promote sediment transport and contribute to the development and maintenance of CPW morphology. Previous studies of plunging flows have relied on coarse-scale field observations and labor-intensive laboratory experiments to investigate their dynamics. Here, we use eddy-resolving computational fluid dynamics models to examine plunging-flow behavior, building on experimental evidence that lateral channel constriction induces plunging flows. Using large-eddy simulations (LES) of laboratory-scale flows, we found that the optimal constriction for generating plunging flows is approximately 35% under lower-flow conditions but increases to 50% at higher flows because of changes in inlet velocity and flow depth. At higher discharge rates, channel constriction further amplifies the plunging effect, producing substantial shear stresses near the point of velocity inversion. Increasing constriction also leads to greater velocity variance and more intermittent pulsing of plunging flows, both of which are likely to enhance incision potential. These findings highlight the need to refine bedrock incision models to better represent the dynamic and complex nature of plunging flows, moving beyond the simplified steady-flow assumptions that underpin most landscape evolution models.
