The advancement of wind energy as an alternative source to hydrocarbons depends heavily on research activities in turbulence modeling and experimentation. The velocity deficit behind wind turbines affects the power output and efficiency of a wind farm. Being able to simulate the wake dynamics of a wind turbine effectively can result in optimum spacing, longer wind turbine life, and shorter payback on the wind farm investment. Two-equation turbulence closure models, such as k–ε and k–ω, are used extensively to predict wind turbine performance and velocity deficit profiles. The application of the Reynolds stress model (RSM) turbulence closure method has been limited to few studies where the rotor is modeled as an actuator disk (AD). The computational cost associated with RSM has made it challenging for simulations where the rotor is discretized directly; however, with advances in computer speed and power coupled with parallel computing architecture, RSM may be a better turbulence closure option. In this research, wind tunnel experiments were conducted, using hot-wire anemometry, to measure the velocity deficit profiles at different wake locations behind a small-scale, three-bladed, horizontal-axis wind turbine (HAWT). Experiments were also performed with two and three HAWTs in series to evaluate the change in velocity deficit and turbulence intensity (TI). High-speed imaging with an oil-based mist captured the vortices produced at the blade tips and showed the vortices dissipated approximately three rotor diameters downstream. Computational fluid dynamics (CFD) simulations were performed to predict the velocity deficit at wake locations matching the experiments. The Reynolds stress model was applied to a fully discretized rotor with a tower and nacelle included in the simulation. A steady-state moving reference frame (MRF) model was created with the computational domain subdivided into rotating and stationary domains. The MRF results were used as an initial condition for time-accurate rigid body motion (RBM) simulations. The RBM CFD simulations showed excellent agreement with experimental measurements for velocity deficit after properly accounting for experimental boundary effects. Isosurfaces of the Q-criterion highlighted the vortices produced at the blade tips and were consistent with high-speed images.

Feasibility of increasing lift and decreasing drag by drilling narrow span-wide channels near the leading edge of NACA 4412 airfoils is investigated. It is proposed to drill two-segment slots that allow some of the incoming air to flow through them and then exit from the bottom surface of the airfoil. Such slots can result in an increased local pressure and thereby higher lift. Length, width, inlet angle, and exit angle of slots are varied to determine optimum configurations. Aerodynamic performance at different angles of attack (AoAs) and the chord-based Reynolds number of 1.6 × 106 is investigated. It is concluded that longer and narrower slots with exit streams more aligned with the air flowing below the airfoil can result in a higher lift. Also, in order to keep the slotted airfoils beneficial for AoAs greater than zero, it is proposed to (a) slightly lower the slot position with respect to the original design and (b) tilt up the first-leg by a few degrees. For the best design case considered, an average improvement of 8% is observed for lift coefficient over the entire range of AoA (with the maximum increase of 15% for AoA = 0), without any significant drag penalty.