Formation and structure of vortex systems around a translating and oscillating airfoil

Within the Sonderforschungsbereich 25 the development of the leading-edge vortex system and its influence on the unsteady aerodynamic forces were investigated experimentally and numerically. Two different flow configurations were considered : an airfoil at a fixed high angle of attack in unsteady flow and an oscillating airfoil in steady flow. The experimental study was performed using a Water-Ludwieg-Tunnel. The velocity fields were visualized by particle path methods, while the aerodynamic forces were measured by a three-component strain gauge balance. Numerical investigations are performed by finite-volume method, based on the Navier-Stokes equations for incompressible flow. In both cases processes were observed similar to dynamic stall : The triple vortex structure, which consists of the primary, secondary, and tertiary vortex were formed. The secondary vortex cuts the connection between the primary and the tertiary vortex and completes the dynamic stall.