Momentum balance in a fully developed boundary layer over a staggered array of NREL 5MW rotors

3D Reynolds-averaged Navier-Stokes (RANS) simulations of a fully developed wind farm boundary layer over a staggered array of NREL 5MW turbines are presented. The turbine is modeled as an actuator disk and as a fully resolved rotor to compare the effect of the turbine model on the wind farm aerodynamics, in particular the streamwise momentum balance across the farm. Results show that the difference in the turbine model affects the average wind speed through the farm as well as the local flow pattern around each turbine; both contributing to the difference in the prediction of farm performance. Results are also compared with a simple theoretical model of very large wind farms proposed recently. The actuator disk simulations agree very well with the theoretical model, whereas the fully resolved rotor simulations show some consistent and expected differences from the model

Prediction of hydrodynamic forces with and without transition model

International audienc

Analysis of the Unsteady Flow Around a Hydrofoil at Various Incidences

The oscillating hydrofoils used in underwater propulsion devices often experience large variations of the flow incidence, which favors cavitation at large angle of attack, and therefore a severe degradation of the performance, additional flow instability, and even cavitation erosion. These various phenomena make numerical simulations of the flow around oscillating hydrofoils quite challenging, especially in cases where the laminar-turbulent transition usually occurs when the blade has a high angle of attack. In the present study, the unsteady flow around a stationary Clark-Y hydrofoil is simulated at five fix incidence angles using the Star CCM+ software. The results show that the lift coefficient increases continuously with the incidence angle up to 15°, even after a separation vortex is generated near the trailing edge. Then, as a slight stall occurs at 20°, the lift coefficients obtained with the k-ω SST and SST Re teta transition models become significantly different, mostly because of the different prediction of laminar to turbulence transition at the hydrofoil leading edge. Under deep stall condition at 25°, the flow is much more complex and the hydrofoil performance decreases dramatically. The lift force predicted by the SST transition model is more periodic than with the SST k-ω model. Although the general vortex evolution predicted by the two turbulence models is similar, the local pressure experiences larger amplitude variations with the k-ω SST model, as can be also observed from the evolution of the lift coefficient