Numerical optimization of axial turbine with self-pitch-controlled blades used for wave energy conversion

Abstract

SUMMARY Wells turbines are among the most practical wave energy converters despite their low aerodynamic efficiency and power produced. It is proposed to improve the performance of Wells turbines by optimizing the blade pitch angle. Optimization is implemented using a fully automated optimization algorithm. Two different airfoil geometries are numerically investigated: the standard NACA 0021 and an airfoil with an optimized profile. Numerical results show that each airfoil has its own optimum blade pitch angle. The present computational fluid dynamics optimization results show that the optimum blade pitch angle for NACA 0021 is +0.3° while that of the airfoil with an optimized profile equals +0.6°.The performance of the investigated airfoils is substantially improved by setting the blades at the optimum blade pitch angle. Both the turbine efficiency and tangential force coefficient are improved, especially at low flow rate and during turbine startup. Up to 4.3% average increase in turbine efficiency is achieved by optimizing the blade pitch angle. A slight improvement of the tangential force coefficient and decrease of the axial force coefficient are also obtained. A tangible increase of the stall‐free operating range is also achieved by optimizing the blade pitch angle. Copyright © 2013 John Wiley & Sons, Ltd.

High performance ocean energy harvesting turbine design–A new casing treatment scheme

“…Efforts have been made to increase the performance of the Wells turbine by changing duct geometry [2], designing monoplane and biplane Wells turbine [3], optimizing blade profile and thickness [4], modifying airfoil profile [5e7], making non-symmetric airfoil blade shape [8] and non-uniform tip gap [9], inserting end plate [10], sweeping [11,12], changing blade pitch angle [13,14], etc. Other efforts involve modification of guide vane angle [15e17], bidirectional flow [18], variable chord [19], bi-plane unidirectional blade [20], counter rotating blade [21,22], hysteretic behavior with unsteady flow [23], etc.…”

Wells turbine blade profile optimization for better wave energy capture

“…For better understanding and comparison between turbines with different blade profiles, the turbine damping coefficient and the critical pneumatic power are presented in normalized forms in Figures 12 and 13. The normalized turbine damping coefficient B* represents the ratio between the turbine damping coefficient B T [Equation (15)] and the damping coefficient of the original turbine B T,original…”

Wells turbine for wave energy conversion: a review

“…A numerical optimization algorithm based on CFD simulation is implemented in order to optimize the blade pitch angle in [126]. The standard NACA 0021 and an optimized profile (AOP) are numerically investigated.…”