Use of streamnormal forces within an array of tidal power harvesters

Abstract

Tidal energy is a renewable and promising energy source. Turbines are deployed under water in marine channels where there is a fast tidal current. The first arrays have only recently been deployed and there is no consensus yet on the optimal array design. In this paper, we explore whether the maximum harvestable power can be increased by using harvesters or flow deflectors that exert a side force in the streamnormal direction to oppose the expansion of the streamtube. The power harvesting and the side force exertion are modelled with sink terms in the two-dimensional Reynolds-averaged Navier-Stokes equations. We found that the power limit increases linearly with the side force, and it should be exerted from the upstream side edges of the array. We conclude that future arrays might not be made only of turbines that harvest power, but also of deflectors such as vertical wings of size comparable to a turbine. The promising results of this theoretical study may direct new research on the use of deflectors to maximise the power harvested by tidal arrays.