Force Variations Related to Flow Pattern Changes Around a High-Camber Thin Wing

Abstract

The aim of this paper is to report and analyze experimental results on forces generated by a high-camber thin section with a sharp leading edge, namely a curved plate with 22.3% relative camber, and measurements of the flow field, in a nominally 2D flow. A wide range of angle of attack [-10°; 32°] is investigated for three values of the Reynolds number across the transitional range. Unusual polar curves are observed with sharp variations of lift with the angle of attack. At low incidence, the lift coefficient increases faster that 2PI/radian. Moreover, very different behaviors occur for Reynolds numbers lower or higher than ~10^5. For small or negative angles of attack, the lift coefficient is negative (downward lift) at small Reynolds numbers, but positive (upward lift) at higher Reynolds numbers. The velocity field is investigated with Particle Image Velocimetry. Variations of lift are related to changes in the topology of the flow field around the section. These results help to better understand the flow around a high-camber and thin section, and provide a detailed benchmark database in a simple geometry for model validations. As strong Reynolds number effects are evidenced, this database would be particularly useful to assess the performance of transition models.