Flow characterization for in-stream energy sites

Thesis (Ph.D.)--University of Washington, 2018A successful in-stream energy project requires an accurate description of the flow characteristics. Numerical models are commonly used to detect feasible locations for energy extraction, but such models have limitations in resolution and accuracy, thus field measurements are crucial for their calibration and validation. In combination with numerical models, high-resolution observations of flow velocities in both time and space are needed to specify the location of turbines, estimate turbine design loads, and to evaluate their interactions with the environment. Promising sites for in-stream energy extraction have strong currents (greater than 1 m/s), and field measurements in such conditions are challenging. Hence, most field measurements are sparse and of limited duration. Efficient measurement techniques that can accurately map turbulent flows in space for long periods of time are critical as the in-stream energy industry reaches a commercial stage. In this thesis, traditional and novel methods are applied to the characterization of turbulent flows at several locations already selected for in-stream energy extraction. In addition, a new technique is developed to capture the wake of a full-scale hydrokinetic turbine under steady state conditions. First, new five-beam acoustic current Doppler profilers (ADCPs) are demonstrated to measure turbulence parameters through the water column at two locations within Puget Sound, WA. The low Doppler noise and high-sampling frequency of these new profilers allow for the observation of the turbulent inertial subrange (typically obscured in previous generations of ADCPs), and the addition of the fifth beam allows for a direct estimation of the Reynolds stresses from along-beam velocity fluctuations. These results are then used to assess a turbulent kinetic energy budget, in which depth profiles of the turbulent kinetic energy dissipation and production rates are compared. Long-term measurements of tidal currents across Admiralty Inlet, WA, are performed using ADCPs mounted onboard ferries. This cost-effective method results in a new map of tidal currents harmonics across and through the depth of the inlet. Obtained results agree well with those from stationary measurements, significantly expanding the available data here. Applications to residual flows are explored. Finally, a new method is developed for detailed flow field mapping prior to and during the operation of a full-scale hydrokinetic turbine. A drifting five-beam ADCP, the Nortek Signature 1000, is used to evaluate the spatial extent of the turbine's wake and its evolution in terms of mean flow velocities and turbulence parameters. These results are valuable for numerical modelers, turbine designers, and stakeholders, as they quantify the environmental effects of in-stream energy extraction under real conditions