Abstract
In this contribution, unsteady three-dimensional numerical simulations of the water flow through a horizontal axis hydrokinetic turbine (HAHT) of the Garman type are performed. This study was conducted in order to estimate the influence of turbine inclination with respect to the incoming flow on turbine performance and forces acting on the rotor, which is studied using a time-accurate Reynolds-averaged Navier-Stokes (RANS) commercial solver. Changes of the flow in time are described by a physical transient model based on two domains, one rotating and the other stationary, combined with a sliding mesh technique. Flow turbulence is described by the well-established Shear Stress Transport (SST) model using its standard and transitional versions. Three inclined operation conditions have been analyzed for the turbine regarding the main stream: 0° (SP configuration, shaft parallel to incoming velocity), 15° (SI15 configuration), and 30° (SI30 configuration). It was found that the hydrodynamic efficiency of the turbine decreases with increasing inclination angles. Besides, it was obtained that in the inclined configurations, the thrust and drag forces acting on rotor were lower than in the SP configuration, although in the former cases, blades experience alternating loads that may induce failure due to fatigue in the long term. Moreover, if the boundary layer transitional effects are included in the computations, a slight increase in the power coefficient is computed for all inclination configurations.
Highlights
Climate change, associated with negative impacts resulting from overexploitation and the use of fossil fuels, has induced environmental problems of great magnitude but has generated an awakening in the scientific community and governments
The performed CFD simulations have been unsteady dynamics of the flow was dealt with the Shear Stress Transport (SST) turbulence model, where the boundary layer laminar-to-turbulent transitional effects have been included
The computed efficiency curves for the inclined configurations were compared with those provided with the so-called cos3 γ correlation; as a result, the correlation sufficiently approximates the CFD results for tip speed ratios close to the maximum efficiency point, it presents noticeably differences for values of λ outside of this range
Summary
Climate change, associated with negative impacts resulting from overexploitation and the use of fossil fuels, has induced environmental problems of great magnitude but has generated an awakening in the scientific community and governments. Using hydrokinetic energy as a renewable source for generating electricity is nowadays one of the most active fields of research [2]. Water currents such as oceans and rivers constitute a wide and almost unexploited source for renewable energy generation. Many developing countries are crossed by rivers which carry significant volumetric water flow along the year. This fact could be a revolutionary scenario for remote populations which could use this energy source if effective and low-cost energy harnessing mechanisms are developed [3].
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