A correction to the enhanced bottom drag parameterisation of tidal turbines

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Title: A correction to the enhanced bottom drag parameterisation of tidal turbines
Authors: Kramer, SC
Piggott, MD
Item Type: Journal Article
Abstract: Hydrodynamic modelling is an important tool for the development of tidal stream energy projects. Many hydrodynamic models incorporate the effect of tidal turbines through an enhanced bottom drag. In this paper we show that although for coarse grid resolutions (kilometre scale) the resulting force exerted on the flow agrees well with the theoretical value, the force starts decreasing with decreasing grid sizes when these become smaller than the length scale of the wake recovery. This is because the assumption that the upstream velocity can be approximated by the local model velocity, is no longer valid. Using linear momentum actuator disc theory however, we derive a relationship between these two velocities and formulate a correction to the enhanced bottom drag formulation that consistently applies a force that remains close to the theoretical value, for all grid sizes down to the turbine scale. In addition, a better understanding of the relation between the model, upstream, and actual turbine velocity, as predicted by actuator disc theory, leads to an improved estimate of the usefully extractable energy. We show how the corrections can be applied (demonstrated here for the models MIKE 21 and Fluidity) by a simple modification of the drag coefficient.
Issue Date: 19-Feb-2016
Date of Acceptance: 8-Feb-2016
URI: http://hdl.handle.net/10044/1/29467
DOI: https://dx.doi.org/10.1016/j.renene.2016.02.022
ISSN: 1879-0682
Publisher: Elsevier
Start Page: 385
End Page: 396
Journal / Book Title: Renewable Energy
Volume: 92
Copyright Statement: © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Sponsor/Funder: Engineering & Physical Science Research Council (E
Engineering & Physical Science Research Council (E
Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/L000407/1
Keywords: 0906 Electrical And Electronic Engineering
0913 Mechanical Engineering
Publication Status: Published
Appears in Collections:Faculty of Engineering
Earth Science and Engineering
Centre for Environmental Policy
Faculty of Natural Sciences

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