上海交通大学学报

上海交通大学学报 ›› 2020, Vol. 54 ›› Issue (3): 285-294.doi: 10.16183/j.cnki.jsjtu.2020.03.008

• 学报（中文） • 上一篇    下一篇

浸没及非浸没刚性短植被群对异重流运动特性的影响

熊杰1，2，袁野平1，林颖典1   

  1. 1. 浙江大学 海洋学院， 浙江 舟山 316021； 2. 中国建筑第三工程局有限公司， 武汉 430073
  • 出版日期:2020-03-28 发布日期:2020-04-09
  • 通讯作者: 林颖典，男，副教授，电话(Tel.)：15700151516；E-mail：kevinlin@zju.edu.cn.
  • 作者简介:熊杰(1994-)，男，江西省丰城市人，硕士生，研究方向为异重流运动特性的实验室模拟.
  • 基金资助:
    国家重点研发计划(2016YFC0402406), 国家自然科学基金(11672267, 41506101)资助项目

Effects of Submerged and Emergent Rigid Short Vegetation Canopies on Gravity Current Dynamics

XIONG Jie 1,2,YUAN Yeping 1,LIN Yingdian 1   

  1. 1. Ocean College, Zhejiang University, Zhoushan 316021, Zhejiang, China; 2. China Construction Third Engineering Bureau Co., Ltd., Wuhan 430073, China
  • Online:2020-03-28 Published:2020-04-09

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摘要： 利用一系列开闸式异重流水槽实验，研究不同刚性植被密度和高度的短植被群对异重流运动的影响.通过高速摄像机拍摄异重流的运动过程，利用粒子图像测速技术得到局部流场结构.结果表明：异重流在流经短植被群时，存在半椭圆形和三角形两类轮廓；运动过程分为坍塌阶段和自相似阶段，并且植被可以显著促进异重流从坍塌阶段向自相似阶段的转换，但对坍塌阶段的头部速度影响不显著.当无量纲植被高度(植被高度与水深比值)为0.21，植被密度为18.0%时，异重流会同时沿着植被上方及植被间运动，植被上方的异重流密度较植被内大，因此会产生瑞利-泰勒不稳定性.此外，异重流在植被区域流动的掺混系数随头部位置而递减，且较无植被情况小.在流入浸没式植被后，异重流会以植被顶部为新的“底部边界”，形成负涡度带，但植被顶端的异重流仍与环境水体发生掺混形成正涡度带.植被会减缓异重流运动速度，进而降低正涡度带的强度，并且植被密度与正涡度的抑制程度成正相关.

关键词: 异重流； 短植被群； 浸没式刚性植被； 界面不稳定； 掺混系数

Abstract: A series of lock-exchange experiments are carried out to study effects of vegetation density and height for short vegetation canopies on gravity current motions. A high-speed camera is applied to acquire the evolution process of the gravity currents, and a particle image velocimetry system is used to investigate the microstructures of gravity currents. Experimental results show that when the gravity current flows through short vegetation canopies, the gravity currents profile will be in the shape of classic ellipse or a well-defined triangle. Movement process is divided into slumping phase and self-similar phase. Furthermore, vegetation canopies can significantly promote the transition of gravity currents from slumping phase into self-similar phase, but cannot influence the current front velocity during the slumping phase. As the non-dimensional vegetation height (the ratio of vegetation height to water depth) is 0.21 with the vegetation density being 18.0%, the gravity current flows along the upper edge of vegetation and within vegetation at the same time. Since the current density on the top of vegetation is larger than that within vegetation, the Rayleigh-Taylor instability occurs. In addition, the entrainment coefficient of gravity current within vegetation decreases as the current moves further, and it is smaller than that without vegetation. When the density current moves into the submerged vegetation, some current climbs on the top of the vegetation where a new “bottom boundary” for gravity current is formed and negative vorticity is produced. In the upper boundary of the current, the current keeps mixing with the ambient fluid and induces the positive vorticity. The results also suggest that vegetation reduces the current speed as well as the strength of positive vorticity, and the vegetation density is proportional to the reduction degree of the positive vorticity.

Key words: gravity currents; short vegetation canopies; submerged rigid vegetation; interface instability; entrainment coefficient

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