Abstract
For low-head water sources, hydrokinetic turbines are potential technologies that can offer viable renewable energy options to extract energy in the rivers and water channels. In this paper, three-dimensional unsteady simulations were carried out on a straight-bladed Darrieus hydrokinetic turbine with NACA 0018 airfoil to analyse the flow physics in vortex separation at an operating tip speed ratio of 1.7 with turbine solidity of 0.224. The vortex separation or flow separation, and flow reattachment have been studied concerning the instantaneous power coefficients of the turbine at different azimuthal positions. It was observed that the steady decline in turbine power coefficient occurs from the azimuthal angle of 90° as vortex separation begins. A dip into the negative region was found 60° later. The re-entering into the positive power coefficient region is attributed to flow reattachment between 180° and 210°.
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