Numerical Studies On Performance Improvement Of Self-Rectifying Air Turbine For Wave Energy Conversion

Abstract

Wells turbine is a self-rectifying air turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column (OWC) into mechanical energy. The Wells turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and lower tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. In the present computational investigations, the performance of the Wells turbine is predicted for constant chord (CONC) rotor, variable chord (VARC) rotor and variable chord rotor using guide vanes on upstream and downstream side of rotor. The predicted values of pressure drop with flow coefficient shows almost a linear variation and are in agreement with the experimental results. Power coefficient obtained from the VARC rotor with and without guide vanes is more than the CONC rotor at all flow coefficients. Due to recovery of rotor exit kinetic energy by the downstream guide vanes, the pressure drop across the turbine has increased, resulting in higher energy transfer and consequently higher turbine efficiency in VARC rotor.

A detailed analysis of the unsteady flow within a Wells turbine

“…Thanks to the continuous increase in computing power, the performance of complex system can nowadays be reproduced by means of Computational Fluid Dynamics (CFD). The impacts of hub-to-tip ratio and aspect ratio, 13 blade sweep, 14 radially variable airfoil profiles, 15 tip gap, 16,17 duct shape, 18 blade skew, 19 blade profile, 20 and casing treatments 21 have been studied numerically.…”

A comparison of computational and experimental results of Wells turbine performance for wave energy conversion

“…In order to investigate hysteretic phenomena of a Wells turbine, numerical investigations have been conducted under unsteady flow conditions [9][10][11]. Dhanasekaran and Govardhan [12] investigated the performance and aerodynamics of a Wells turbine with NACA0021 constant chord blade, while performance improvement using a variable chord blade was studied by Govardhan and Chauhan [13]. This paper describes the use of CFD to investigate the performance of a Wells turbine with various uniform tip clearances, in which the size of the gap between the tip and casing is the same from the leading to trailing edges of the turbine blade.…”

Combined Casing Groove and Blade Tip Treatment for Wave Energy Harvesting Turbine

“…The blade with variable chord with guide vanes showed better starting characteristics [7]. The turbine performance can be improved by modifying blade setting angle [8].…”