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

Abstract

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.

Review on the conversion of thermoacoustic power into electricity

“…An advantage of the radial impulse turbine over the axial version is the reduced amount of axial thrust, which relaxes the fatigue on the bearings of the generator. 103 Besides this difference, both impulse turbines are characterized by a wide operating range with efficient performance and good starting characteristics, where the latter is ensured by the use of guide vanes. However, the large incidence angle of the flow at the downstream guide vane also causes an increase in aerodynamic loss, which can not be avoided due to the symmetry needed for operating in bidirectional flows.…”

“…An overview of the optimum design values for a wide range of aspects is given in the work of Das et al for Wells and impulse turbines in OWC's. 103 Just as in conventional steady flow turbines, the Wells and impulse turbines can be extended with additional rotors and guide vanes to introduce multiple stages. 106 This can be done in an effort to enhance the coupling between the turbine and working gas and to increase the power output.…”

“…108,104 The impulse turbines have good starting characteristics and no problems of stall at higher flow rates, and therefore have the advantage of a wider operating range where a change in Reynolds number does not have much influence on the turbine efficiency. 103 However, this does come at the cost of a smaller peak efficiency then the Wells turbines, with the radial impulse turbine generally having a smaller efficiency than the axial version. 103 Finally, as suggested by de Blok et al for thermoacoustics, 55 the possibility of scaling bidirectional turbines to the MW range seems plausible.…”

Bidirectional impulse turbines for thermoacoustic devices

“…An advantage of the radial impulse turbine over the axial version is the reduced amount of axial thrust, which relaxes the fatigue on the bearings of the generator. 110 Besides this difference, both impulse turbines are characterized by a wide operating range with efficient performance and good starting characteristics, where the latter is ensured by the use of guide vanes. However, the large incidence angle of the flow at the downstream guide vane also causes an increase in aerodynamic loss, which can not be avoided due to the symmetry needed for operating in bidirectional flows.…”

“…An overview of the optimum design values for a wide range of aspects is given in the work of Das et al for Wells and impulse turbines in OWCs. 110 Just as in conventional steady flow turbines, the Wells and impulse turbines can be extended with additional rotors and guide vanes to introduce multiple stages. 113 This can be done in an effort to enhance the coupling between the turbine and working gas and to increase the power output.…”