Modeling the near-wake of a vertical-axis cross-flow turbine with 2-D and 3-D RANS

The near-wake of a vertical-axis cross-flow turbine was modeled numerically via blade-resolved k-omega shear stress transport (SST) and Spalart-Allmaras Reynoldsaveraged Navier-Stokes (RANS) models in two and three dimensions. The results for each case were compared with the experimental measurements of the turbine shaft power, overall streamwise rotor drag, mean velocity, turbulence kinetic energy, and momentum transport terms in the near-wake at one diameter downstream. It was shown that 2-D simulations overpredict turbine loading and do not resolve mean vertical momentum transport, which plays an important role in the near-wake's momentum balance. The 3-D simulations fared better at predicting performance, with the Spalart-Allmaras model predictions being closest to the experiments. The SST model more accurately predicted the turbulence kinetic energy, while the Spalart-Allmaras model more closely matched the momentum transport terms in the near-wake. These results show the potential of blade-resolved RANS as a design tool and a way to "extrapolate" experimental flow field measurements. Published by AIP Publishing.