Hydrokinetic energy conversion devices provide the facility to capture energy from water flow without the need of large dams, impoundments, channels or deviation of the water as in conventional hydroelectric centrals. Hydrokinetic systems are intended to be used in streams, either natural (rivers, estuaries, marine currents) or artificially built channels. This article reviews the advances made over the last 10-15 years regarding the three-dimensional computational fluid dynamics modeling and simulation of this type of turbines. Technical aspects of model design, employed boundary conditions, solution of the governing equations of the water flow through the hydrokinetic turbine and assumptions made during the simulations are thoroughly described. We hope that this review will encourage new computational investigations about hydrokinetic turbines that contribute to their continuous improvement, development and implementation aimed to sustainable use of water resources and addressed to solve the problem of lack of electricity supply in small, isolated populations. Keywords CFD • Hydrokinetic turbine • Simulation • Horizontal axis turbine • Axial flow water turbine List of symbols A Cross-sectional area of the rotor (m 2) A ∞ Water area upstream the turbine (m 2) A d Actuator disk area (m 2) A disk Disk area (m 2) A exit Diffuser exit area (m 2) A w Water area downstream the turbine (m 2) a Axial flow induction factor

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.

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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.

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Abstract. This study presents three-dimensional full transient numerical simulations of a horizontal axis hydrokinetic turbine, HAHT with particular emphasis on the analysis of its hydrodynamic characteristics. Hydrokinetic turbine performance is studied using a time-accurate Reynolds-averaged NavierStokes (RANS) commercial solver. A physical transient rotorstator model with a sliding mesh technique is used to capture changes in flow field at a particular time step. A shear stress transport (SST) turbulence model has been employed to model the turbulent features of the flow. The studied rotor has three blades, based on NACA4412 airfoil. Two operation conditions have been considered: shaft parallel to the incoming flow (SP configuration) and shaft inclined an angle  around 30 o regarding the main stream (SI configuration). As a result, the decrement of the hydrodynamic performance of the turbine with the inclined axis is quantitatively evaluated regarding that of the parallel axis. Moreover, a preliminary study of the vorticity dynamics in the wake of the inclined rotor is performed

The application of computational fluid dynamics (CFD) in wind turbine design and analysis is becoming increasingly common in research on wind energy, resulting in a better knowledge of the aerodynamic behaviour of rotors. Due to the deformation of blade airfoils on account of icing, a significant drop in aerodynamic performance brings wind turbines to lose considerable portions of their productivity. Estimating power degradation due to icing via 3D simulation, although it is essential to capture the three-dimensional turbulence effects, is very costly in computational resources despite technological development it then becomes unfeasible when it comes to different operation scenarios to estimate icing originated power losses. The Quasi-3D simulation based on the CFD-BEM method is a practical alternative for generating wind turbines power curves. It showed effectiveness in predicting performance up to a certain level. More than few studies in the literature have adopted this approach to generate the power curve for both clean (un-iced) and iced-up wind turbines. However, the methodology was not adequately presented and discussed for wind turbine icing. This paper reviews the results of almost all the up-to-date published papers that approached this method, summarizing the findings and federates the research in that field to conclude with concrete facts and details that advance research in this domain.