Flow–vegetation interactions is an interdisciplinary research area with applications in the management of coastal waters, lakes, and watercourses. Due to an emerging interest in the cultivation of seaweeds, this study seeks to develop a sound understanding of the physical interactions between flow and seaweeds. This is achieved via experiments in a laboratory flume using plastic-made models of blades of the seaweed species Saccharina latissima. In the experiments, strain gages, a digital camera, and acoustic Doppler velocimeters were used for measuring drag forces, blade movements (reconfiguration), and flow velocities. The study involved experiments with single blades and with pairs of tandem blades at different spacing between the blades. The revealed mechanisms controlling the dynamics of seaweed blade models varied depending on the ratio of blade length to eddy length scale. The drag coefficient of seaweed blade models appeared to be dependent on the Reynolds number, the Cauchy number, and the ratio of blade length to integral turbulence length scale. Turbulence had a primary role in controlling blade model dynamics and its drag coefficient. Seaweed blade models affected the flow in their wakes by increasing the turbulence intensity and reducing the mean longitudinal velocity. These effects on the flow are the reason for which, in a pair of tandem blades, the drag force experienced by the downstream blade is lower than that experienced by the upstream blade.
The work described in this publication was undertaken during the Ph.D. study of Davide Vettori at the University of Aberdeen funded by a scholarship from the Northern Research Partnership, Scotland. The authors gratefully acknowledge the help of Michael Boddie, Elisa Bozzolan, Euan Judd, and Henry Lecallet in collecting extensive data sets used in this publication. Stuart Cameron and Euan Judd greatly assisted in developing video analysis routines which is highly appreciated. The authors also thank technicians Roy Gillanders and Benjamin Stratton for thorough technical support of the experiments and required infrastructure. Two anonymous reviewers provided insightful comments that have been gratefully incorporated in the final version.
- Drag force
- Flow–vegetation interaction
- Physical modelling