First Advisor

Raul Bayoan Cal

Date of Award

Winter 3-11-2022

Document Type

Thesis

Degree Name

Bachelor of Science (B.S.) in Environmental Engineering and University Honors

Department

Environmental Engineering

Language

English

Subjects

reynolds shear stress, offshore wind turbine, quadrant analysis, wave phase, turbulence, offshore wind energy

Abstract

As the need for a reliable renewable energy supply is increasing, many have looked to offshore wind because they hold more potential for power production than onshore wind. Interests in expanding offshore wind energy has brought along many challenges when it comes to understanding the complex dynamics experienced offshore, including the relationship between the wind-turbine generated wakes and ocean waves. This experimental study characterizes the relationship between Reynolds shear stress and the phase of surface waves above the air-sea interface in the wind-turbine wake region. The experimental setup combines a wave tank, wind tunnel, and a fixed-bottom wind turbine. Particle image velocimetry (PIV) is performed for three successive planes to visualize wave-wake interactions far downstream. Triple decomposition is performed to resolve phase-dependent velocity fields. Quadrant analysis was utilized to provide insights into momentum transport and Reynolds stress composition. Shear stress profiles behind the turbine were observed during three wave conditions: no wave, long wave, and short wave. Ensemble averaged profiles reveal a rotating wake region of reduced momentum behind the turbine that is not dependent on wave features. Phase averaged velocity profiles show Reynolds stress wave-induced phase-averaged fluctuations that follow the curvature of the waves. Significant Reynolds stress dependence on wave phase was observed in all four quadrants and altered the position of the turbulence events. The results indicate a correlation between surface waves and turbulent wind-wake interactions that can be utilized for design optimization and control strategies.

Available for download on Saturday, February 25, 2023

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