Dynamic stall onset and the road to recovery

Dynamic stall on pitching airfoils is an important practical problem that affects for example rotary wing aircraft and wind turbines. It also comprises a number of interesting fundamental fluid dynamical phenomena such as unsteady flow separation, vortex formation and shedding, unsteady flow reattachment, and dynamic hysteresis. Experimental time-resolved velocity field and surface pressure data for two-dimensional pitching airfoils with various reduced frequencies were analysed using different Eulerian, Lagrangian, and modal decomposition methods. These complementary analyses resulted in the identification of the chain of events that play a role in the stall onset and the stall recovery process. The individual events will be characterised by their governing time-scales and flow features and recent modelling attempts will be presented.