Unsteady Viscous Flow on Oscillating Airfoils

Incompressible laminar and turbulent flows over flat plates and airfoils have been investigated numerically and experimentally in unsteady flow conditions. Important differences were found between laminar and turbulent flat plate flows over a wide range of oscillation frequencies. Also, the importance of unsteady effects on laminar boundary layers was found to diminish rapidly with increasing longitudinal pressure gradients, whereas turbulent separation on airfoils was significantly affected by oscillatory motion when the incidence approached the stall angle. The calculated hysteresis in turbulent separation followed in a qualitative sense the well-known trends of dynamic stall delay and reattachment. However, the numerical analysis failed to indicate some of the important features of dynamic stall observed in the present experiment and in previous studies.