浸没式植被对异重流运动特性的影响

Study on Effects of Submerged Vegetation on Gravity Currents Dynamics

摘要:

为研究异重流流经浸没式植被时的运动特性，以天然河道中的植被为原型，对植被环境中异重流的运动规律进行了试验研究，并采用异重流头部（最前缘）速度代表其运动速度.研究结果表明，异重流流经短植被群（长度30 cm、高度3 cm）时大部分异重流在植被顶部向前运动，流过植被后依然保持典型轮廓，呈现一个先加速、后匀速、然后迅速减速、最后缓慢线性减速的运动过程；流经长植被群（长度80 cm、高度6 cm）时大部分异重流被阻挡于植被后方，仅有少部分异重流流出植被后缓慢向前运动，呈现先加速、后匀速、然后迅速减速、最后缓慢运动的过程.异重流运动过程分为坍塌阶段和自相似阶段，植被的阻挡效应可以减小坍塌阶段向自相似阶段的转化点，并且转化点与植被阻挡效应呈负相关，但与异重流浓度关系不显著.异重流与环境水体掺混界面涡度值为正，与水平底床界面涡度值为负；当植被的阻挡效应较强时，异重流流出植被后掺混和卷吸作用较弱，且出流量与异重流浓度呈正相关.

Abstract:

To study the movement characteristics of gravity currents propagated submerged vegetation, taking the vegetation in natural rivers as prototype, and front velocity of gravity currents represented velocity of gravity currents. The results showed that gravity currents propagated the short vegetation (length 30 cm, height 3 cm), it ridded on the top of vegetation and moved forward, and then contain the typical contour outflow the vegetation; presented a movement process that accelerated first, followed by uniform forward, then decreased , and finally slowed down. When gravity currents propagated the long vegetation (length 80 cm, height 6 cm), part of it was blocked behind the vegetation and only a part of gravity currents out of vegetation and moved forward, represented the process of first accelerating, then uniform velocity, then rapidly decelerating, and finally slow velocity. The movement process of gravity currents was divided into slumping phase and selfsimilar phase, and the blocking effect of vegetation can reduce the position of slumping phase translated into selfsimilar phase, and transform position was negatively related to the barrier effect of vegetation, but it was not related to the density of gravity currents. The vorticity values at the interface between gravity currents and environmental water was positive, and it was negative at the interface with horizontal bed. When the vegetation had a strong blocking effect, the mixing and entrainment effect was weak after gravity current propagated out of vegetation, and the outflow positively correlated with the density of gravity currents.