Author(s): Stuart M. Cameron; Vladimir I. Nikora; Ismail Albayrak; Oliver Miler; Mark Stewart; Fabio Siniscalchi
Keywords: River turbulence; Aquatic vegetation; Particle Image Velocimetry; Flow-plants interactions
Abstract: A stereoscopic particle image velocimetry (PIV) system for use in shallow rivers was developed and deployed to study the interactions between turbulent flow and a Ranunculus penicillatus plant patch in its native environment. Statistical moments of the velocity field were calculated utilising a new method of reducing the contribution of measurement noise, based on the measurement redundancy inherent to the stereoscopic PIV method. The data reveal that the wake of the plant patch was dominated by the presence of a free shear layer induced by the plant drag. Plant motion, estimated from the PIV images, was characterised by travelling waves that propagate along the plant with a velocity nearly equal to the local mean velocity, indicating a direct coupling between turbulence and the plant motion. The characteristic frequency of the plant velocity fluctuations (~1Hz) suggests that the plant motion is dominated by large eddies with dimensions comparable to the flow depth or plant length. Plant and fluid velocity fluctuations were, in contrast, found to be strongly correlated only over a narrow elevation range above the top of the plant, supporting a conjecture that the shear layer turbulence is a key contributor to the plant motion. This talk is devoted to the memory of Professor Stephen E. Coleman – long-term friend and collaborator.