Numerical Investigation of a Darrieus Rotor for Low-head Hydropower Generation

The aim of this paper is to numerically investigate the performance of a cross-flow water turbine of the Darrieus type for very low head hydropower applications. The interest for this kind of vertical axis turbine relies on its versa- tility. For instance, in the field of renewable energy, this kind of turbine may be considered for different applications, such as: tidal power, run-of-the-river hydroelectricity, wave energy conversion. Until now, low head hydropower, with heads less than 2 meters, has remained scarcely developed due to the relatively low energy density, which makes the cost of generation higher than traditional hydropower applications. However, in the spirit of distributed generation, the use of low head hydropower can be reconsidered, having the advantage of lower electricity transmission losses due to the localization near the consuming area. Nonetheless, it is fundamental to improve the turbine performance and to decrease the equipment costs for achievement of “environmental friendly” solutions and maximization of the “cost-advantage”. In the present work, the commercial CFD code Fluent is used to perform 2D simulations, solving the incompressible Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations discretized by means of a fi- nite volume approach. The implicit segregated version of the solver is employed. The pressure-velocity coupling is achieved by means of the SIMPLE algorithm. The convective terms are discretized using a second order accurate up- wind scheme, and pressure and viscous terms are discretized by a second-order-accurate centered scheme. A second order implicit time formulation is also used. Turbulence closure is provided by the realizable k− [turbulence model. The model has been validated, comparing numerical results with available experimental data