Determining the Spatial Coherence of Turbulence at MHK Sites
Kilcher, Levi F.
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Although turbulence is thought to be a key variable in the performance and survivability of Marine Hydrokinetic turbines, it has not been fully characterized at sites where they will be deployed. In particular, the conventional metrics of turbulence intensity and turbulent kinetic energy spectra only describe the turbulence at a point. Spatial information is required to estimate the loading across a rotor, for example, and to understand the short-term evolution of turbulence in the vicinity of a device (for potential use in feed-forward control algorithms). Here, we describe a method to collect and analyze data for determining the spatial coherence of turbulence at marine hydrokinetic turbine deployment sites. The approach uses multiple compliant moorings equipped with acoustic Doppler velocimeters and inertial motion units. Analysis of data from previous deployments of a single mooring is used to demonstrate the method, and future deployments are discussed. It is expected that coherence will be highly dependent on scale, with high coherence for large-scale eddies, and low coherence for the smaller, inertial-scale eddies.