Low Reynolds Number Surge Response of a Flat Plate Wing at 90 Degrees Incidence

© 2017, American Institute of Aeronautics and Astronautics Inc. All rights reserved. This article presents an experimental investigation into the unsteady force response of a at plate wing when accelerated from rest at 90° incidence to the free stream direction. The work was performed to test a low order model developed by the NATO AVT-202 task group for pitching and surging wings at low Reynolds numbers. The model expresses the force response on a wing as the sum of circulatory components due to vortex dynamics, and non-circulatory components due to added mass. Force measurements, flow visualisation, and PIV measurements were taken for a fast and slow acceleration rate to relatively isolate the effect of added mass. Measurements suggest that the modified Wagner function can give a surprisingly reasonable prediction of vortex growth during the acceleration phase of a surging wing, however, incorrectly predicts vortex growth at steady state. It is proposed that added mass is a mechanism that generates vorticity, thus PIV measurements of circulation of the vortex pair can also contain the impulse due to added mass. When PIV measurements are compensated for added mass, good agreement between the drag predicted by the low order model and force balance measurement is shown.