Abstract
This paper presents a numerical study of the effects of the inclination angle of the turbine rotation axis with respect to the main flow direction on the performance of a prototype hydrokinetic turbine of the Garman type. In particular, the torque and force coefficients are evaluated as a function of the turbine angular velocity and axis operation angle regarding the mainstream direction. To accomplish this purpose, transient simulations are performed using a commercial solver (ANSYS-Fluent v. 19). Turbulent features of the flow are modelled by the shear stress transport (SST) transitional turbulence model, and results are compared with those obtained with its basic version (i.e., nontransitional), hereafter called standard. The behaviour of the power and force coefficients for the various considered tip speed ratios are presented. Pressure and skin friction coefficients on the blades are analysed at each computed turbine angular speed by means of contour plots and two-dimensional profiles. Moreover, the pressure and viscous contributions to the torque and forces experienced by the hydrokinetic turbine are examined in detail. It is demonstrated that the reason behind the higher power coefficient predictions of the transitional turbulence model, close to 6% at maximum efficiency, regarding its standard counterpart, is the smaller computed viscous torque contribution in the former. As a result, the power coefficient of the inclined turbine is around 35% versus the 45% obtained for the turbine with its rotation axis parallel to flow direction.
Highlights
The fast development of renewable energy technology is responsible for the increase of the renewable sources in the world energy production (2537 GW in 2019, with an increase of 7% regarding 2018, constituting nowadays more than one-third of the global power production)
The first one is the blade element momentum (BEM) approach as it is implemented in the software package Qblade, and the second method is the lifting line free vortex wake (LLFVW), included in the same package
This paper has addressed the computational fluid dynamics (CFD) numerical simulation of an existing Garman-type hydrokinetic turbine (HK) turbine which was empirically designed and was in operation in the Cauca River, in the southwest of Colombia some years ago
Summary
The fast development of renewable energy technology is responsible for the increase of the renewable sources in the world energy production (2537 GW in 2019, with an increase of 7% regarding 2018, constituting nowadays more than one-third of the global power production). The axial machines have is rotor normal to the current, while the crossflow turbines operate with their rotation axis oriented 90◦ with respect to the flow direction in a horizontal or vertical arrangement The former are more efficient in energy conversion, the latter are independent of stream orientation, which makes them attractive for being employed as tidal CEC. Given that reliable experimental data on Aquavatio do not exist, this paper deals with the detailed CFD simulation of the Aquavatio HK aimed at two objectives: building the efficiency curve and characterizing its hydrodynamic behaviour depending on the inclination angle of the turbine rotation axis regarding the flow direction (see Figure 2 below) and rotor angular speed ω. The dependence of the intermittency contours with the turbine axis orientation angle is illustrated for three turbine rotational velocities
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