| Summary: | Numerical simulations are used to explore the potential for
local blockage effects and dynamic tuning strategies to enhance the performance of turbines in tidal channels. Fulland partial-width arrays of turbines, modelled using the
volume-flux-constrained actuator disc and blade element
momentum theories, are embedded within a two-dimensional
channel with a naturally low ratio of drag to inertial forces.
For steady flow, the local blockage effect observed by varying the cross-stream spacing between the turbines is found to
agree very well with the predictions of the two-scale actuator disc theory of Nishino and Willden (2012, “The efficiency
of an array of tidal turbines partially blocking a wide channel”, J. Fluid Mech., vol. 708, pp. 596–606). For oscillatory
flow, however, results show that, consistent with the findings
of Bonar et al. (2019, “On the arrangement of tidal turbines in rough and oscillatory channel flow”, J. Fluid Mech.,
vol. 865, pp. 790–810), the shorter and more highly blocked
arrays produce considerably more power than predicted by
two-scale theory. Results also show that, consistent with the
findings of Vennell (2016, “An optimal tuning strategy for
tidal turbines”, Proc. R. Soc. A., vol. 472, p. 20160047),
the ‘dynamic’ tuning strategy, in which the tuning of the turbines is varied over the tidal cycle, can only produce significantly more power than a temporally fixed turbine tuning if
the array has a large number of turbine rows or a large local
blockage ratio. For all cases considered, trends are consistent between the two turbine representations but the effects
of local blockage and dynamic tuning are found to be much
less significant for the more realistic tidal rotor than for the
idealised actuator disc
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