Numerical investigation on the loss audit of Wells turbine with exergy analysis

As one of the most promising methods for harnessing ocean wave energy, the oscillating water column device has been intensively investigated, especially the Wells turbine within the device. However, owing to the low efficiency of the Wells turbine, it is essential to provide a deep insight into the loss audit and loss quantification. The scope of this work is to explore the main loss mechanisms due to the irreversibility. The aerodynamic losses and associated flow behaviors within four typical working conditions were quantified and analyzed in detail based on entropy generation and exergy analysis. The loss weight of the Wells turbine indicates that the secondary flow loss coupled with the friction loss is the largest, 34%, under the stall condition. The blade tip streamlines show that a large-scale vortex structure on the blade suction caused by the interaction of the leakage flow and the suction side flow is one of the main reasons of the decreasing blade loading and growth of low-energy fluids. Moreover, the exergy loss gradually increases with the increasing angle of attack, leading to a dramatic drop of the second law efficiency from 0.52 at the maximum torque point to 0.22 at the stall condition.