Performance Improvement of Crossflow Air Turbines for Wave Energy Conversion in Oscillating Water Columns: A CFD Study

Abstract

The coastal countries have a valuable renewable energy source in the form of ocean waves, which, if harnessed effectively using wave energy converters (WEC), could significantly enhance their electrical energy supply. Numerous technologies have been researched, put forth, examined, and sometimes tested in real ocean conditions at full scale. One of the most promising WECs is the oscillating water column (OWC), which has a modest number of moving parts that are all above the water level with a relatively simple mechanism. Although the Wells turbine is a widely used power takeoff (PTO) system of OWC, having higher peak efficiency than the crossflow air turbine (CFAT), it shows a narrow operational flow range. This operational flow range issue could be addressed by deploying CFATs. Only a few researches have been conducted on the CFAT as the PTO for OWCs. The present study focuses on numerical model-building and validation using the available experimental data to investigate the performance characteristics for optimized nozzle shapes for CFAT. For the base model, numerical results are compared to experimental data for validation. The geometry of the nozzle is optimized to achieve maximum efficiency under steady-state conditions. The nozzle entry arc angle is varied between 90° to 150°. The optimized model reached a peak efficiency of 68% with a steady high efficiency for broader operating conditions (broader flow range). Therefore, the proposed design addresses the issue of the narrow band of the Wells turbine while potentially improving the efficiency of the existing CFAT model.