On the turbulent flow dynamics in flexible emergent canopies

Experimental investigations concerning the turbulent characteristics of flow within flexible emergent canopies were conducted in the water channel facility in UT Dallas. The canopies were mimicked through a staggered arrangement of single flexible blades of 5 mm width and frontal area per unit volume, a varying from 0.02 to 0.08 cm^-1. The relative fluid forcing to the restoring forces in the blade was achieved by varying the channel-to-canopy height ratio and incoming velocities. The dynamics of fluid flow was captured using time-resolved particle image velocimetry and the plate deformation was characterized through high-speed cameras. The results indicate that the deformation of flexible vegetation highly modulated form drag, turbulence intensity levels and turbulent eddy scales, and the velocity statistics exhibited a distinctive variation when the vegetation posture altered from emergent to submerged conditions with the growth of water flow speed. A revised Cauchy number was developed to incorporate the emergent canopy effects on blade posture.