Novel Tidal Energy Harnessing System Utilizing Quadruple Bi-directional Turbine Arrangement

Abstract

In the modern era global power demand rises implicitly with exponentially growing power needs. As the global warming becomes a critical factor, emission regulations are set to minimize and eventually seize the traditional power production methods in near future. As a solution, this research aims on presenting a novel methodology for harnessing energy from tidal current streams. In hydro-power sector Cross Flow Turbine (CFT) or “Banki-Michell Turbine” have become a popular choice over the years. But in ocean renewable energy field, limited amount of research has being done to assess the capability of this particular turbine. CFT is a bi-directional turbine, as the turbine runner imparts unidirectional behavior regardless of the flow direction. In this study, tidal passage with cross sectional area of 756.25 m2 having length of 87.5 m consists of equally spaced, 6.1 m diameter four CFT’s housed within separate augmentation channels. These specially shaped augmentation channels act as turbines converging and diverging (vice-versa) nozzles passages for the fluid passage. Each turbine runner consists of 18 blades having thin profile. The turbine setup was computer modeled and meshed. The volumetric mesh combines of 28 million, Hexahedral and Tetrahedral mesh elements. Runner blades were extra fined with close mesh elements to capture the boundary layer effect accurately. The quad-turbine setup was simulated with an open sea domain to gain accurate flow field behavior also to eliminate abrupt turbulence behavior pass the tidal passage. Numerical calculations of the turbine setup was carried out using commercial computational fluid dynamics (CFD) code ANSYS CFX. The turbine cluster yields a maximum power output of about 500 kW at optimum tip speed ratio (TSR) of 0.4 for the designed average tidal flow velocity of 2.5 ms-1, with a maximum of about 18% efficiency. As the previous research studies suggests, the efficiency values of tidal current turbines are generally being lower becomes a bearable factor in this study as well. Compared with prevailing tidal turbines designs, the CFT system requires no mechanical or electrical interactions to change the turbine runner blade directions. The simple design of CFT system economically beneficial due to low manufacturing cost and requires considerably less maintenance.