Abstract
Tidal currents are a renewable energy resource and the work presented is in the field of harnessing tidal currents for electrical power generation. The main objective of the research is to provide information on rotational flow effects, caused by the spinning of the earth, around obstacles on the sea floor, in support of developing robust design of an underwater turbine array. This research looks at a gravity based linear array, a single turbine deep, with its largest dimension several kilometers long. The primary goal is to model a Taylor column above a linear array. The Taylor column has closed streamlines or stagnant flows inside of it and the flows around the column accelerate asymmetrically. The layout design of the array is intended to minimize the effect of the stagnant flows by predicting the location where closed streamlines could develop. The design is for the array and not for a turbine. Also, the locations where the energetic flows through the array have the longest periods are identified.Numerical modeling with ANSYS Fluent failed repeatedly to accurately model rotational effects around an obstacle with a minimal relative current so as to form a Taylor column. Instead, Johnson's (1982) analytical solutions for quasigeostrophic flows over elongated topography are used to study how the blocking parameter influences streamlines with changes in velocity typical of a tidal change. The streamlines illustrate the location over an array where the flows are accelerated and also where closed streamlines form.While Taylor columns are not expected to form distinctively in the short slack tides, the results indicate that rotational flows manifest on the southern end of an obstruction oriented N-S with an eastward flow. Viewing an array as the obstruction, the south end would experience drops of velocity with the changing tide first. The study was done in the f-plane, meaning the Coriolis parameter was held constant. The turbines attempting to harness the current acceleration around a Taylor column would physically need to be placed opposite from the side of the array experiencing low Rossby numbers first. Such turbines would need to be sensitive to currents <1m/s.