DYNAMIC INTERACTION OF A MODEL SCALE TIDAL TURBINE IN NON-HOMOGENEOUS SHEARED TURBULENCE*

Tidal turbines face considerable challenges due to elevated turbulence and velocity shear in tidal environments. The fluctuations in the turbine power due to the inflow turbulence enhance fatigue loading and pose stability issues for the electrical grid, necessitating costly synchronizers. Mimicking such inflow conditions in controlled laboratory settings allows a detailed understanding of the dynamic interaction of the inflow with the turbine. The current study generates a range of inflow conditions from quasi-laminar to elevated turbulence with and without shear and coherent structures using an active grid in a water tunnel. We analyze the response of a model-scale turbine to these conditions and establish their power spectral characteristics. The results showed that despite the anticipated increase in loading with elevated turbulence and shear, turbine performance diminishes under these conditions for optimum tip-speed ratios compared to quasi-laminar cases. The inflow scales primarily influence the shape and trends of the power spectra up to the turbine frequency, beyond which rotor dynamics dominate. The power spectra exhibit strong correlations with low-frequency large-scale fluctuations, confirmed by generating larger integral length scales, while correlations decrease for high-frequency fluctuations. Additionally, the turbine responds to coherent structures in the inflow, with notable energy peaks potentially intensifying loading on the devices. A marked correlation exists between turbine power fluctuations and these coherent structures in the inflow. Lastly, our study demonstrates that current turbine power spectral models can replicate the shape of the spectra, albeit with some limitations.