Skip to main content

Research Repository

Advanced Search

On the turbulence dynamics induced by a surrogate seagrass canopy

Houseago, Robert C.; Hong, Liu; Cheng, Shyuan; Best, James L.; Parsons, Daniel R.; Chamorro, Leonardo P.


Robert C. Houseago

Liu Hong

Shyuan Cheng

James L. Best

Daniel R. Parsons

Leonardo P. Chamorro


The distinct turbulence dynamics and transport modulated by a common seagrass species were investigated experimentally using a flexible surrogate canopy in a refractive-index-matching environment that enabled full optical access. The surrogate seagrass replicated the dynamic behaviour and morphological properties of its natural counterpart. The flows studied were subcritical with Froude numbers Fr < 0.26 and concerned five Reynolds numbers Re ϵ [3.4 × 104, 1.1 × 105] and Cauchy numbers Ca ϵ [120, 1200]. Complementary rigid canopy experiments were also included to aid comparative insight. The flow was quantified in wall-normal planes in a developed region using high-frame-rate particle image velocimetry. Results show that the deflection and coordinated waving motion of the blades redistributed the Reynolds stresses above and below the canopy top. Critically, in-canopy turbulence associated with the seagrass lacked periodic stem wake vortex shedding present in the rigid canopy, yet the flexible canopy induced vortex shedding from the blade tips. Inspection of spatial and temporal characteristics of coherent flow structures using spectral proper orthogonal decomposition reveals that Kelvin - Helmholtz-type vortices are the dominant flow structures associated with the waving motion of the seagrass and that modulated the local flow exchange in both rigid and flexible canopies. A barrier-like effect produced by the blade deflections blocked large-scale turbulence transport, thereby reducing vortex penetration into the canopy. In addition, we uncovered a transition from sweep-dominated to ejection-dominated behaviour in the surrogate seagrass. We hypothesise that the vortices created during the upward blade motion period play a major role in the sweep-to-ejection-dominated transition. Conditionally averaged quadrant analysis on the downward and upward blade motion supports this contention.


Houseago, R. C., Hong, L., Cheng, S., Best, J. L., Parsons, D. R., & Chamorro, L. P. (2022). On the turbulence dynamics induced by a surrogate seagrass canopy. Journal of Fluid Mechanics, 934, Article A17.

Journal Article Type Article
Acceptance Date Dec 14, 2021
Online Publication Date Jan 14, 2022
Publication Date Mar 10, 2022
Deposit Date Mar 11, 2022
Publicly Available Date Oct 27, 2022
Journal Journal of Fluid Mechanics
Print ISSN 0022-1120
Electronic ISSN 1469-7645
Publisher Cambridge University Press
Peer Reviewed Peer Reviewed
Volume 934
Article Number A17
Public URL


Published article (4 Mb)

Copyright Statement
© The Author(s), 2022. Published by Cambridge University Press.<br /> This is an Open Access article,<br /> distributed under the terms of the Creative Commons Attribution licence (https://creativecommons. org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium,<br /> provided the original work is properly cited.

You might also like

Downloadable Citations