Optimal design of air turbines for oscillating water column wave energy systems: A review

Oscillating water column wave energy harvesting system uses pneumatic power to run a turbine and generate power. Both reaction (mainly Wells turbine) and impulse type turbines are tested in oscillating water column system and the performances are investigated. Reaction turbines are easy to install, and the operating range is narrow and possesses higher peak efficiency. On the contrary, impulse turbines have the wider operating range and lower peak efficiency. Some of the key parameters for Wells turbine are solidity, tip clearance, and the hub-to-tip ratio. Significant performance improvement is possible by redesigning the turbines using optimization techniques. Till date, surrogate modeling and an automated optimization library OPAL are commonly used in optimization of oscillating water column air turbines. In this article, various types of oscillating water column turbines are reviewed, and optimization techniques applied to such turbines are discussed. The Wells turbine with guide vane has the maximum efficiency, whereas the axial-impulse turbine with pitch-controlled guide vane has the widest operating range. Turbines with optimized geometry have better overall performance than other turbines.