  Depth-averaged shallow water models are widely used for the large-scale
simulation of tidal turbine arrays. The relatively low computational complexity
of this approach allows for layout optimisations aimed at improving the total
array power output as well as an assessment of large-scale environmental
impacts. In order to assess the suitability of using depth-averaged models to
optimise array configurations, a comprehensive comparison between the wake
profiles and power outputs predicted by a 2D shallow water model and a 3D
actuator disc momentum (ADM) model is presented. Initially, a viscosity
sensitivity analysis is presented to outline the limitations associated with
using a constant eddy viscosity in the depth-averaged model and to outline the
importance of correctly calibrating this value in line with the freestream
velocity magnitude. Thereafter, the depth-averaged OpenTidalFarm (OTF) tool is
used to optimise the positions of an array of 32 turbines in an ideal channel
and the 3D Fluidity ADM-RANS model is used to assess the accuracy of the OTF
predictions for the first time. It is shown that with the help of corrected
power calculations a good agreement between the two models can be achieved,
thus demonstrating the value of the eddy viscosity calibration implemented in
the depth-averaged model.
