Mapping performance of a marine energy harvesting turbine for flow coefficient and Reynolds number with varying Mach number through an automated optimization technique

The manuscript investigates the limitations of Wells turbines in oscillating water columns for extracting energy from ocean waves, highlighting their low operating range and average power output. The authors employ an automated optimization technique to identify the optimal inlet velocity and rotational speed that correspond to the maximum turbine efficiency. The study reveals that the turbine’s performance is mainly determined by the flow coefficient, Reynolds number (Re), and Mach number (Ma). To understand the impact of these non-dimensional parameters, the turbine performance was examined by varying the flow parameters in such a way that Re covers a wide range (2.6 × 105 up to 1.56 × 106). For each flow coefficient, the turbine performs well up to a certain value of Re. Subsequently, Re-regimes where the turbine gives maximum efficiency were mapped. For low values of Re, the flow coefficient can be varied within a relatively wide range while keeping a high performance. However, this range will decrease with increasing Re (keeping in mind that Ma changes as well). Overall, this study confirms the importance of considering not only the flow coefficient, but also additional non-dimensional parameters when analyzing and comparing the performance of turbomachines.