VORTEX INITIATION DURING DYNAMIC STALL OF AN AIRFOIL

The flow field around an oscillating airfoil is evaluated numerically, using the stream function-vorticity formulation of the Navier-Stokes equations. An algebraic turbulence model, adapted from the Baldwin-Lomax model, is included in solving the time-averaged Reynolds equations. Computed pressure distribution for turbulent flow past a stationary airfoil is compared with measurements. Finally, for the oscillating airfoil cases, the computations are performed in order to determine the history of pressure distribution and to identify the nature of the vortex initiation on the suction surface for laminar and turbulent flow. Our results for laminar flow show that minute circular shaped vortices are formed on the surface prior to the dominant vortex formation. Flattened vortices are formed on the surface in turbulent flow, prior to the formation of the dominant large vortex structure.