Explanation Of Scatter Phenomenon In Wind-Tunnel Experiments For Airfoils At High Incidences By The Multi-Equilibrium States Of Separated Flow

Coupled with k - omega SST turbulent model, the unsteady Reynolds-averaged Navier - Stokes equations are solved in the time-domain to obtain the steady and/or unsteady separated flow for airfoils at high incidences. Different kinds of vibrations are designed for the airfoils to simulate different disturbances. The effects of different disturbances on the separated flow are studied, especially at high incidences when the multi-equilibrium states phenomenon for the separated flow exists. It is found that, for the given Reynolds number and airfoils with thickness larger than 2 0 %, multi-equilibrium states exist for the separated flows around the airfoils, and the equilibrium state of the separated flow may transit under certain disturbances at some range of incidences. Generally, the plunging disturbance and pitching disturbance are more effective than the forward-backward disturbance in leading to the equilibrium state of the separated flow transiting from one state to another. The average aerodynamic force will change when the equilibrium state of the separated flow-field transit. These phenomena can be an explanation for the poor repeatability and scatter phenomenon of aerodynamic characteristics for configurations at high incidences in wind-tunnel experiments.