Portland State University. Department of Mechanical and Materials Engineering
Raúl Bayoán Cal
Term of Graduation
Date of Publication
Master of Science (M.S.) in Mechanical Engineering
Mechanical and Materials Engineering
Fluid mechanics, Wind power, Wakes (Fluid dynamics), Turbulence, Flow visualization
1 online resource (iii, 49 pages)
The interest and benefits of offshore wind energy has also brought along legitimate design challenges for engineers. Most notably, the complex interaction between wind and turbine is further complicated by the addition of dynamic ocean waves. This dynamic coupling between wind, wave, and turbine is not fully understood. Even small improvements in wind turbine performance are welcome, so characterizing a fundamental dynamic in offshore energy is necessary to optimize design. Experimentation and simulation have been used to characterize inflow and turbine wakes and separately, wind-wave interactions. But only simulations have just begun to look at the wind, wave, and turbine wake interaction, albeit with great difficulty. In this study, a scaled fixed-bottom wind turbine was placed in a custom wind tunnel containing a wave tank able to generate waves. Particle image velocimetry (PIV) was performed on three successive image planes in order to visualize wake development far downstream. The images were used to characterize the wave profile, wake center, and velocities. The data was used to decompose a standard ensemble mean further into phase-averaged means based on wave shape and location (phase). These decompositions were used to look at local phase-dependent trends for several quantities. The results illustrate that the wake profile is phase dependent and a wake pumping effect, due to the waves, is observed. Local momentum maxima, which are obscured by the ensemble mean, are revealed in the phase-averaged means at the wave crests. The waves do not transfer momentum, per se, but do convert streamwise momentum into vertical momentum. In addition, there is a phase-dependent oscillation in both the horizontal (streamwise) direction of the wake, as well as the vertical displacement of the wake. The shear stress, advection, and turbulence terms show to have an imbalance along the vertical direction of the turbine. These results have implications for design optimization, siting, design, and power extraction.
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Fercak, Ondrej, "Fixed Bottom Wind Turbine Wave-Wake Interaction" (2021). Dissertations and Theses. Paper 5732.