Lift, drag and surface pressure measurements are performed on a wing section of the NREL S826 wind turbine airfoil at eight Reynolds numbers ranging from 0.5 × 10 5 to 6.0 × 10 5 . Alongside with the measurements two types of Reynolds averaged Navier-Stokes (RANS) simulations are performed, one of which includes a laminar to turbulent transition model. The lift and drag characteristics are observed to be dominated by low Reynolds number effects for Re < 0.7×10 5 , related to the presence of laminar separation bubbles (LSBs) on the suction side of the profile. For Re ≥ 0.7 × 10 5 the airfoil's performance is rather independent of the Re-number for the present free stream turbulence intensities, while significantly higher peak lift is measured than in earlier experiments on the same airfoil. At high angles of attack, strong three-dimensional spanwise surface flow distribution reminiscent of a single stall cell is observed. The RANS simulations in a two-dimensional domain including the Langtry-Menter γ − Re θ transition model accurately predict lift and drag coefficients as long as the flow is fairly attached. Further, the γ − Re θ model simulations are observed to predict the location and average size of the LSBs in this region.
Two-dimensional, two component particle image velocimetry (PIV) measurements of the guide-vane wake and vaneless space for a high head Francis model turbine are presented. Measurements have been carried out with a fixed head and rotational speed for a set of guide-vane openings representative of part load, high load and best efficiency operating points. The measured trajectory and strength of the guide vane wake for the different operating points is discussed in conjunction with the periodic velocity oscillations. It is hoped that the present measurements will aid in further analysis as well as provide an additional set of data for validation of numerical analyses.
A test of the v
2 − f k − ϵ turbulence model for the flow around the Francis-99 hydrofoil geometry is conducted in order to assess it’s accuracy of trailing edge vortex shedding prediction. The model is based on the k − ϵ turbulence model, but needs no wall damping function, and also allows near-wall turbulence anisotropy. For reference, the model results are compared with the the SST k − w, in addition to preliminary experimental results previously published. It is indicated that the v
2 − f k − ϵ model gives at least as good, or better results than the more commonly used SST k − w model for the present case, though further measurements are needed in order to make a proper conclusion.
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