The influence of drag parameter on submerged vegetation flow simulation using a porous approach

In simulating vegetated flows using the porous approach, the reasonableness of the drag coefficient significantly impacts the calculation results. This study employs large eddy simulation (LES) to quantitatively investigate the effect of drag parameters on key flow characteristics in submerged vegetated flows. The results indicate that changes in the drag coefficient significantly alter the velocity in the middle of the vegetation layer and near the water surface in the free-flow layer. Compared with longitudinal velocity, the drag coefficient has a more pronounced effect on the vertical distribution of Reynolds stress, especially its peak at the top of the vegetation layer. The porous approach can accurately reproduce the vertical distribution of longitudinal velocity and Reynolds stress, consistent with experimental measurements, only when shear-scale flow dominates. Due to the high-intensity secondary flow under moderate vegetation density, fluctuations in the drag coefficient have a more significant impact on the numerical results than in very dense vegetation. Therefore, selecting the drag coefficient value should be done cautiously, especially in the absence of experimental measurements for validation.