Hydrodynamic performance of vegetation surrogates in hydraulic studies: a comparative analysis of seaweed blades and their physical models

Vegetation surrogates have been extensively used in laboratory experiments for studying flow-vegetation interactions. However, it remains unclear how accurately the surrogates replicate the prototype vegetation in terms of hydrodynamic performance, even when similarity conditions are followed. To address this matter, we compare the hydrodynamic performance of seaweed blades of the species Saccharina latissima with performance of their surrogates, which were designed based on similarity considerations. To assess the hydrodynamic performance of samples, we measured flow velocities upstream and downstream of the samples, their vertical movements, and the drag forces exerted on them. The obtained data reveal that the mechanisms governing flow-blade interactions are essentially the same for live blades and their surrogates. Even though the surrogates successfully replicate many aspects of live blade dynamics, they experience weaker drag force and reconfiguration, likely because of their simplified morphologies that differed from the live blades at small scales. To enhance similarity in hydrodynamic performances, we suggest employing comprehensive similarity conditions at all relevant scales.