Hydrodynamic and transport phenomena at the interface between flow and aquatic vegetation : from the forest to the blade scale
Name
881812906-MIT.pdf
Description
Full printable version
Size
19.49 MB
Format
Adobe PDF
Checksum (MD5)
508b976f17f70e1d2fe4e686e4a49d99
Author(s)
Rominger, Jeffrey T. (Jeffrey Tsaros)
Advisor(s)
Heidi M. Nepf.
Date Issued
2014
Publisher
Massachusetts Institute of Technology
Abstract
From the canopy scale to the blade scale, interactions between fluid motion and kelp produce a wide array of hydrodynamic and scalar transport phenomena. At the kilometer scale of the kelp forest, coastal currents transport nutrients, microorganisms and spores. But, kelp forests exert a drag force on currents, causing the flow to decelerate and divert as it encounters the canopy, affecting the fate of species transported by the current. We identify a dimensionless flow-blockage parameter, based on canopy width and density, that controls both the length of the flow deceleration region and the total flow in the canopy. We further find that shear layers at the canopy edges can interact across the canopy, providing additional exchange between the canopy and the surrounding water. At the sub-meter scale, kelp blades are the photosynthetic engines of kelp forests, but are also responsible for the majority of the fluid drag force on the plants and for acquiring nutrients directly from the surrounding water. These blades are highly flexible structures which move in response to the local fluid forcing. Recent studies documenting changes in blade flexural rigidity in response to changes in flow demonstrate a need for understanding the role blade flexural rigidity plays in setting both drag forces, and nutrient flux at the blade surface. We create a model physical system in which we investigate the role of blade rigidity in setting blade forces and rates of scalar exchange in a vortex street. Using a combination of experimental and theoretical investigations, we find that, broadly, forces are higher for more flexible blades, countering the adage that "going with the flow" is beneficial. Below a critical value of the dimensionless blade rigidity, inertial forces from the rapidly deforming blade become significant, increasing the likelihood of blade failure. Nutrient transport is also affected by blade rigidity. As blades deform, they alter the relative fluid motion at the blade surface, affecting nutrient fluxes. We develop a novel experimental method that simulates nutrient uptake to a blade using the transport of a tracer into polyethylene. Through these experiments and modeling, we demonstrate that increased blade flexibility leads to increased scalar transport. Ultimately, blade flexural rigidity affects both mass and momentum flux.
Description
Thesis: Ph. D. in Environmental Fluid Mechanics, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.
116
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 227-235).
Subjects
Civil and Environmental Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
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