Marine energy resource
Modelling large arrays of tidal turbines
Added roughness model
Introduction
Individual tidal stream generator units are
limited in capacity and in general cannot
completely block a tidal stream. If tidal
stream power is to make a significant
contribution to the energy mix, multi-row
arrays of tidal turbines will need to be built,
so tools are required to investigate the
possible effects of a large array on the flow.
Based on the theory of rough-wall
boundary layer flow over obstacle
arrays, these models assume that the
momentum balance in a large array
reaches a spatially-averaged equilibrium
Modelling tidal stream arrays
Physical models of tidal stream turbine arrays
are difficult to produce due to scale. Numerical
models tend to be divided into three types of
increasing complexity:
1. Added roughness (boundary layer) models
A general obstacle array
2. Wake superposition models
In order to make the model useful,
3. Field models
assumptions need to be made about
the flow profile below the obstacle
height (hub height) and the friction with
1 row
2 …
the ground as a proportion of the drag
on the obstacles (turbines).
st
nd
Application of new model
The added roughness model may be
used within existing coastal models to
simulate large arrays and their effect on
the tidal regime.
Added roughness/boundary layer type model (top left)
Wake superposition model (bottom left) Field model (right)
Strengths of different models
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Simulated flow speed change (m/s) from natural
tidal flow state when added roughness is applied
in a numerical model of Portland Bill
£££
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