Two operating points were selected for simulation. The lower power The power and thrust for each of the simulations was computed andcase corresponds to a 9 m/s wind speed and 10.3 RPM rotational compared to the results published by Riso1.speed. The higher power case entails a wind speed of 11 m/s anda rotational speed of 11.9 RPM. Steady RANS simulations usingthe Spalart-Allmaras turbulence model were performed for bothconditions, while a full sliding mesh DES simulation was performedonly for the lower power case. All simulations were performedusing a 64 core AMD Opteron cluster with an Infiniband messagepassing network. Steady state simulations of the full rotor modelrequired approximately 10 hours of compute time on the cluster toreach a steady state solution. Figure 6: Power and thrust comparisons between AcuSolve and Riso simulations.Results The AcuSolve results compare well to the Riso simulations, indicatingThe steady RANS solution provides detailed information about the that the unstructured meshing/finite element solution methodologyperformance of the rotor. The local pressure field on the high and low provides accurate results for this application. Additionally, the DESpressure side of the blade for the lower power case is shown approach is found to provide similar results as the steady RANSin Figure 4. simulations. For this application, the additional compute cost of the DES approach is not warranted if integrated quantities such as power and thrust are the only items of interest. However, this also implies that the DES approach produces accurate results and can be used for inherently transient applications such as acoustic and fluid- structure interaction simulations. Conclusions An unstructured grid based CFD modeling methodology has been developed and successfully used to simulate the flow around a utility Figure 4: Surface pressure distribution on the wind turbine blade. scale wind turbine rotor. The total power and thrust predicted by the simulations compare favorably with results obtained by otherThe CFD solution is also successful at capturing the detailed research groups. To facilitate the ease of performing the full rotorflow structures in the wake of the turbine. Adequately capturing simulations, all gridding was performed using fully automatedthese features requires highly accurate numerical methods to unstructured mesh generation techniques, and post processing waspropagate the wake downstream without the need to use excessive performed using automated batch processing.compute resources. The wealth of insight provided by CFD simulations gives designers and engineers the opportunity to rapidly investigate advanced design concepts and establish the improvements in efficiency, reliability, and cost effectiveness that are required to propel wind power technology into the future. This validation effort represents an important step in achieving these improvements and can easily be extended to encompass more complex physics such as sheared wind conditions, gust events, and fluid structure interaction. Figure 5: Flow structures in the wake of the 5 MW rotor models. References The image on the left depicts iso-surfaces of the Q-criterion 1. UPWIND, Aerodynamics and aero-elasticity. Rotor aerodynamics colored by velocity magnitude. This clearly illustrates the root and tip vortices as well as the trailing edge vortex sheet. in atmospheric shear flows. Niels N. Sorensen. Wind Energy The image on the right is a cut plane showing contours of Department, Risoe National Laboratory, vorticity in the wake of the rotor. www.risoe.dtu.dk/rispubl/art/2007_140_paper.pdf.