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J. Mar. Sci. Eng. 2018, 6(2), 43; https://doi.org/10.3390/jmse6020043

Coupling Numerical Methods and Analytical Models for Ducted Turbines to Evaluate Designs

1
Department of Naval Architecture and Marine Engineering University of Michigan, Ann Arbor, MI 48109, USA
2
V2 Wind Inc., Boston, MA 02116, USA
Current address: 2600 Draper Dr, Ann Arbor, MI 48109, USA.
*
Author to whom correspondence should be addressed.
Received: 27 February 2018 / Revised: 31 March 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
(This article belongs to the Special Issue Marine Propulsors)
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Abstract

Hydrokinetic turbines extract energy from currents in oceans, rivers, and streams. Ducts can be used to accelerate the flow across the turbine to improve performance. The objective of this work is to couple an analytical model with a Reynolds averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) solver to evaluate designs. An analytical model is derived for ducted turbines. A steady-state moving reference frame solver is used to analyze both the freestream and ducted turbine. A sliding mesh solver is examined for the freestream turbine. An efficient duct is introduced to accelerate the flow at the turbine. Since the turbine is optimized for operation in the freestream and not within the duct, there is a decrease in efficiency due to duct-turbine interaction. Despite the decrease in efficiency, the power extracted by the turbine is increased. The analytical model under-predicts the flow rejection from the duct that is predicted by CFD since the CFD predicts separation but the analytical model does not. Once the mass flow rate is corrected, the model can be used as a design tool to evaluate how the turbine-duct pair reduces mass flow efficiency. To better understand this phenomenon, the turbine is also analyzed within a tube with the analytical model and CFD. The analytical model shows that the duct’s mass flow efficiency reduces as a function of loading, showing that the system will be more efficient when lightly loaded. Using the conclusions of the analytical model, a more efficient ducted turbine system is designed. The turbine is pitched more heavily and the twist profile is adapted to the radial throat velocity profile. View Full-Text
Keywords: numerical methods; ducted turbine; computational fluid dynamics; CFD numerical methods; ducted turbine; computational fluid dynamics; CFD
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Knight, B.; Freda, R.; Young, Y.L.; Maki, K. Coupling Numerical Methods and Analytical Models for Ducted Turbines to Evaluate Designs. J. Mar. Sci. Eng. 2018, 6, 43.

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