NUMERICAL STUDIES ON PERFORMANCE IMPROVEMENT OF SELF-RECTIFYING AIR TURBINE FOR WAVE ENERGY CONVERSION

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.