Performance analysis of Savonius hydrokinetic turbine capturing wave energy under different operating strategies

Abstract Horizontal-placed Savonius hydrokinetic turbines extracting energy from the orbital motion of water particles in waves have enormous potential due to their good economic performance and low energy transfer loss. However, as a new concept of cyclical type wave energy converters, horizontal-placed Savonius hydrokinetic turbines are less studied by researchers and suffer from low power performance. This study further optimizes the submerged level and explores the performance of a two-bladed Savonius turbine operating under three new strategies aiming to enhance the turbine's capability of wave energy power generation. The new operating strategies are categorized by the variation rule of theoretical phase angles in the regular wave, which has not been studied yet. Initially, the turbine was tested in a two-meter-deep wave flume to assess the performance of a unidirectional rotating turbine placed at different submerged levels. The test results were applied to validate the reliability of the numerical wave tank, which was established through the unsteady Reynolds-averaged Navier-Stokes equation in conjunction with the Volume of Fluid method. Finally, the performance parameters of the turbine operating under each strategy were calculated with varied phase angles, wave periods, and corresponding rotation speeds to evaluate the turbine's capability accurately and comprehensively through comparing its hydrodynamic characteristics in wave energy conversion. The results demonstrated that the turbine placed at the submerged level of 0.75 D had the fastest rotation speed. The turbine operating under different strategies presented significantly different performances. The maximum energy conversion efficiency of 15.798% was obtained in a single wave cycle of the SHT operating under the phase-unlocked strategy. But for the general continuous wave, the highest efficiency (12.467%) was found under the initial phase-locked strategy, which was 122.904% and 58.211% higher than those of the phase-locked strategy and the phase-unlocked strategy. Besides, under all operating strategies, better performance was found in a shorter wave period, and the optimum phase angle was obtained in the range of 54°-90° and 234°-270°. To conclude, the initial phase-locked strategy is the proper selection for SHT located at the optimum submerged level(0.75D) to extract energy in the regular wave.