坡面植被水流水动力学特性研究

Experimental study on hydraulic characteristics of overland flows under vegetation cover

本实验为人工水草模拟植被覆盖条件下的坡面流水动力学特性研究，以水力学和流体力学基本理论为依据，通过室内定床阻力模拟放水实验，定量的研究了植被覆盖度为9．3％（2500簇／m2）的工况下，不同坡度和流量组合对植被水流各水动力学参数的影响。结果表明：坡面植被水流平均流速随坡度和流量的增大呈递增趋势，可用线性函数或幂函数关系模拟，且线性关系优于幂函数关系；植被坡面流平均水深与流量和坡度之间也存在着显著的线性关系和幂函数关系；植被坡面流的佛汝德数随流量的增加而减小、随坡度的增加而增大，并呈现出一定的幂函数关系，但佛汝德数主要受坡度的控制，流量对佛汝德数的影响很小；阻力系数随雷诺数的变化规律呈单驼峰形式，本实验条件下，在雷诺数为1500～2000时达到最大值，当雷诺数大于2000时，随雷诺数的增加阻力系数反而减小，最后逐渐趋于稳定，可见两者之间并非呈简单的递增或递减关系。

This experiment has been conducted to study hydraulic characteristics of overland flows on a fixed bed laboratory model with simulated vegetation cover of 9.3%, along with an analysis on variations of hydraulic parameters of overland flows under different discharges and different bed slopes using the theories of fluid mechanics and hydraulics. Measurements show that average velocity of water flow on the vegetation slope increases with bed slope and flow rate, and that the relationship can be expressed by either a linear or power function, but with the linear one superior. These two functions can also well fit the relationship of water depth versus bed slope and flow rate. Froude number of the vegetation slope water flow decreases with the increasing flow rate but increases with bed slope, following a power function, but its variation is evidently dominated by bed slope and much less dependent on flow rate. Resistance coefficient of the flows varies in a hump shape, reaching its peak in the Reynolds number range of 1500 to 2000. In the range beyond 2000, it is decreasing inversely with Reynolds number and then gradually approaching a stable value. Thus, the relationship of resistance coefficient versus Reynolds number is not monotonic.