High fidelity turbulence measurements are needed to generate accurate fatigue-load estimates from numerical simulations of marine hydrokinetic turbines. In particular comprehensive turbulence datasets at tidal, river and ocean-current sites are needed. Critical statics of these datasets include: turbulence intensity, mean shear, the turbulent kinetic energy (TKE) spectrum, Reynold’s stresses and spatial coherence of turbulent eddies. Results from the wind industry indicate that these turbulence statistics determine device fatigue loads and performance. Mean shear can induce variable loads across a turbine rotor, for example. The TKE spectrum and Reynold’s stresses quantify the size amplitude and orientation of turbulent eddies that can shake a blade of the entire rotor. The present study focuses on spatial coherence in the turbulence, which is an indicator for length of eddies as a function of their diameter. Longer eddies are likely to induce larger fatigue loads on turbines. ]. We also evaluate the coherence at different separations and interpret the results in terms of the length scales in the ?ow, and we compare with results from a new 5-beam acoustic Doppler pro?ler.
