Scale-dependent drag behavior in modeled plant communities using porous cubic arrays

Modeling plant communities as continuous media with a priori drag coefficients is a widely adopted approach in numerical simulations. However, the selection of appropriate drag coefficients across varying scales of plant communities remains a significant challenge. This study seeks to establish a quantitative relationship between the drag coefficient of individual plants (λi) and that of the entire plant community (λt), while investigating the influences of flow field characteristics and community properties on this relationship. A porous cubic model was used to represent individual plants with the plant community modeled as a cubic array. A Reynolds-averaged Navier–Stokes (RANS)-based canopy turbulence model was utilized to simulate the overall and row-wise drag forces acting on cubic arrays under different inflow velocities, turbulence intensities, and frontal area indices (Λ). Our results indicate that in sparse plant communities, the λt is only 2.3% of the λi, quantified as the coefficient difference index (CDI), with this disparity increasing with larger Λ. In uniformly staggered plant arrays, the drag force per row decreases monotonically with increasing row number, and a configuration of 2–3 rows was found to maximize the entire drag effect under most conditions. An empirical model for CDI as a function of λi and Λ was derived, establishing a link between easily measurable and less directly observable parameters. This model provides a practical framework for evaluating drag effects in plant communities, enhancing the accuracy of numerical simulations, and supporting engineering applications.