The impact of waves and immersion depth on horizontal axis tidal turbine performance

The impact of waves and tip immersion depth on the performance of a 500 mm diameter, two-bladed horizontal axis marine current turbine were investigated experimentally in a towing tank. This study presents results at five different tip immersion depths and with regular and irregular waves. Close proximity to the free-surface had a detrimental effect on turbine performance. Between a tip immersion of 0.055mm and 0.265m (0.11D - 0.53D), the power coefficient decreased by 3 - 10% over the range of tip speed ratios tested. Three different wave forms (two regular and one irregular) were tested, based on metocean conditions of Bass strait, Australia. It was found that the average performance characteristics were largely unaffected by the waves. However, significant fluctuations in instantaneous performance parameters were found over each wave period. with the maximum values coinciding with the wave peak. For the highest energy waves, variations in power and thrust coefficient were found to be 36% and 17% respectively. Irregular waves were found to yield higher frequency fluctuations in power and thrust coefficients over a wave period compared to the regular waves