A Comparison of the NREL 5-MW Wake Characteristics Using Both SOWFA and OVERFLOW2

Abstract

The aerodynamic characteristics of the NREL 5-MW rotor were examined using two numerical simulation tools, an unsteady Reynolds-averaged Navier-Stokes method and a large eddy simulation method. OVERFLOW2 is a fully viscous, 3-D, Reynolds-averaged Navier-Stokes method. SOWFA (Simulator for Offshore Wind Farm Applications) is a wind farm simulation tool based on a large eddy simulation (LES) methodology with a line actuator method to represent rotor forces. Three laminar, steady, and uniform wind speed cases spread over the operating range of the NREL 5-MW turbine were simulated with OVERFLOW2 and SOWFA. The aerodynamic behavior predicted by each of the simulation tools was then analyzed and compared. The primary focus of the study was to compare the rotor wake behavior predicted by each simulation tool. The OVERFLOW2 and SOWFA results were found to have fairly good agreement, though there were some discrepancies. Additional SOWFA simulations were carried out to examine the effect of the size and resolution of the near-wake grid. The downstream length of the near-wake grid had only a small effect over the range examined. The grid resolution had a larger effect on turbine and wake behavior.