Numerical replication and improvement of wind tunnel tests for design and off-design operating points of wind turbine airfoils

Abstract

The rationale for this paper is to get a broader understanding of the operation of the closed-loop atmospheric wind tunnel of the Deutsche WindGuard Engineering GmbH. Acquisition and correction of force coefficients are of critical importance for the disposition of airfoil measurements to the final product. Therefore, the tunnel flow is numerically reproduced for a number of representative wind turbine airfoils at typical operational rotorblade Reynolds numbers. Based on the computed field and surface files, the data processing is mimicked and correction methods are analyzed. Besides the investigation of aerodynamically favourable flow states at low angles of attack, the paper also looks at offdesign operating points in deep stall, where classical correction methods are impractical and steady RANS methods are not appropriate. The comparison between experiment and CFD is contradictory. The lift slope is captured well, but the absolute levels of lift and drag in particular show a significant offset. In the off-design, the CFD approach offers reasonable results but emerges to be insufficient due to the high computational effort.