Dynamic Stall Simulations on a Pitching Finite Wing

Kurzfassung

The aerodynamic effects of dynamic stall on pitching wings and airfoils differ significantly from the static case, as soon as the static stall angle is exceeded. The large drag and pitching moment peaks associated with this phenomenon make it impossible to operate helicopters in flight conditions which trigger dynamic stall over large areas of the rotor blade. To simplify the problem, most of the research on dynamic stall focuses on two-dimensional pitching airfoils. This has lead to an understanding of the process and mechanism of dynamic stall, but has a limited insight into the three-dimensional nature of dynamic stall. There have been a few experimental and numerical studies on full helicopter configurations. These revealed the very complex flow field around the rotor blades, but the combination of downwash, blade-wakevortex interactions and the elasticity of the rotor blades leads to a limited comparability. An approach between these configurations is to use stiff pitching finite wings with defined boundary conditions. In these configurations the blade tip vortex reduces and delays the occurrence of dynamic stall in the surrounding region leading to a strongly three-dimensional flow, see e.g. Le Pape et al. and Lorber.