Abstract

The shaftless ducted turbine (abbreviated as SDT), as an extraordinary innovation in tidal current power generation applications, has many advantages, and a wide application prospect. The structure of an SDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. However, there are some structural differences between a DT and a SDT, which can cause significant discrepancy in the hydrodynamic characteristics and flow features. The present work compares the detailed hydrodynamic-energy loss characteristics of a DT and a SDT by means of computational fluid dynamics (CFD), performed by solving the 3D steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations in combination with the Menter’s Shear Stress Transport (SST k−ω) turbulence model and entropy production model. The results show the SDT features a higher power level at low tip speed ratio (TSR) and a potential reduction in potential flow resistance and disturbance with respect to the DT. Moreover, a detail entropy production analysis shows the energy loss is closely related to the flow separation and the reverse flow, and other negative flow factors. The entropy production of the SDT is lessened than that of the DT at different TSR. Unlike the DT, the SDT allows a large mass flow of water to leak through the open-center structure, which plays an important role in improving the wake structure and avoiding the negative flow along the central axis.

Highlights

  • Published: 27 August 2021The world is increasingly becoming concerned about environmental issues and fossil fuel consumption; the production of electricity from renewable sources can effectively minimize environmental pollution and fossil fuel consumption

  • This paper aims to discover the differences in hydrodynamic-energy loss characteristics between a ducted turbine (DT) and a shaftless ducted turbine (SDT) via the computational fluid dynamics (CFD) tool

  • The hydrodynamic characteristics comparisons between the DT and the SDT are given in Figure 8, in which the power coefficient, CP, thrust coefficient, CT are shown based on the hydrodynamic coefficient definitions, as mentioned before

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Summary

Introduction

Published: 27 August 2021The world is increasingly becoming concerned about environmental issues and fossil fuel consumption; the production of electricity from renewable sources (e.g., wind, hydro, wave, tide, biomass, geothermal, etc.) can effectively minimize environmental pollution and fossil fuel consumption. Tidal current energy will have a great advantage in the future, mainly due to its great potential in electricity generation and high predictability [1,2]. A number of commercial and academic institutions have improved technologies that enable the conversion of energy from tides and currents into electrical power [3]. Technology for extracting energy from tidal currents mainly includes turbine systems and non-turbine systems. Many tidal turbine designs have been proposed throughout the years, configurations and improvements are consistently being conducted. Horizontal axis turbines with two or three blades (similar to wind turbine) are the most successful commercial applications [4]

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