Full HAWT rotor CFD simulations using different RANS turbulence models compared with actuator disk and experimental measurements

Abstract. The development of large-scale wind energy projects has created the demand for increasingly accurate and efficient models that limit a project's uncertainties and risk. Wake effects are of great importance and are relevant for the optimization of wind farms. Despite a growing body of research, there are still many open questions and challenges to overcome. In computational modelling, there are always numerous input parameters such as material properties, geometry, boundary conditions, initial conditions, turbulence modelling etc. whose estimation is difficult and their values are often inaccurate or uncertain. Due to the lack of information of several sources, e.g., uncertainties present in operating conditions as well as in the mathematical modelling, the computational output is also uncertain. It is therefore very important to validate the mathematical models with experiments performed in controlled conditions. In the present paper, the single wake characteristics of a Horizontal-Axis Wind Turbine Rotor (HAWT) and their spatial evolution are investigated with different Computational Fluid Dynamics (CFD) modelling approaches and compared to experimental measurements.

The steady state 3-D Reynolds-Averaged Navier Stokes (RANS) equations are solved in the open-source platform OpenFOAM, using different turbulence closure schemes. For the full-rotor CFD simulations, the Multiple Reference Frames (MRF) approach was used to model the rotation of the blades. For the simplified cases, an actuator disk model was used with the experimentally measured thrust (C_T) and power (C_P) coefficient values. The performance of each modelling approach is compared with experimental wind tunnel wake measurements from the 4th blind test organized by NOWITECH and NORCOWE in 2015. Numerical results are compared with experimental data along three horizontal lines downstream, covering all the wake regions. Wake predictions are shown to be very sensitive to the choice of the RANS turbulence model. For most cases, the ADM under-predicts the velocity deficit, except for the case of RNG k-ε which showed a superb performance in the mid and far wake. The full wind turbine rotor simulations showed good agreement to the experimental data, mainly in the near wake, amplifying the differences between the simplified models.