On the Spectral Response of a Horizontal Axis Tidal Turbine Subjected to Anisotropic Grid Turbulence*

The conversion dynamics from turbulent velocity fluctuations to turbine output are not well understood, particularly for tidal turbines operating in much more severe inflow conditions than their counterparts, like wind energy. These fluctuations have been shown to cause intermittency in the electrical grid for a wind farm creating a need for control devices. To address some of those deficiencies, we have developed a Tidal Turbulence Test Facility (T³F) at Lehigh University which can mimic several turbulence parameters at high-energy tidal sites using a Makita-type active grid. We will present results from our experimental campaign where we investigate the spectral behavior of power and thrust output of a 1:20 model scale tidal turbine subjected to anisotropic inflow conditions. We perform simultaneous upstream velocity (1D from rotor plane) and turbine measurement for different tip-speed ratios. Four inflow conditions are tested: quasi-laminar (QL), double random (DR1) with elevated turbulence intensity (Ti), synchronous (SY1) with Ti similar to DR1 but dominant scales at the grid operating frequency (1Hz), and shear inflow (SH) mimicking the shear profile of tidal sites. The detailed results will be presented and compared based on the power spectral density for each case.