Numerical Modelling of Flexible Submerged Vegetation

This study considered a new approach for representing flexible canopies within large-eddy simulation 18 (LES) using a distributed drag that captures the impacts of reconfiguration (plant bending in response to 19 flow) on both the canopy posture and the canopy drag. The variation in drag coefficient, projected area 20 tensor, and height of the canopy, as a function of local, instantaneous velocity was estimated from 21 theory and empirical functions. The unsteady change in plant posture in response to the passage of 22 turbulence structures (monami) was assessed using established steady-reconfiguration models 23 responding to the unsteady velocity at the top of the canopy. The new drag and plant posture models 24 improved the modeling of highly flexible canopies by more accurately capturing the observed vertical 25 distribution of peak Reynolds stress. When compared to models that do not consider reconfiguration, or 26 that represent it only through a velocity-dependent drag coefficient, the addition of a velocity-dependent 27 canopy posture (unsteady reconfiguration) achieved up to a 56% reduction of the root mean square error 28 (RMSE) for mean horizontal flow velocity and Reynolds stress profiles over the canopy. The RMSE for 29 turbulence intensities and skewness were reduced up to 48% and 56%, respectively.