VORTICITY BALANCE AND TIME SCALES OF A 2-DIMENSIONAL AIRFOIL IN AN UNSTEADY FREE-STREAM

In unsteady aerodynamic research, there exists a long list of operational variables due to the complexity of the flow. For engineering design purposes, parametric study is the conventional approach. In this investigation, an alternative approach is used. It is demonstrated here that the physical insights of the intricate unsteady aerodynamic flow can be understood from a simple fundamental vorticity balance concept. The test configuration is a stationary two-dimensional NACA 0012 airfoil placed at the static stall angle of 12-degrees in an unsteady free stream. A local circulation measurement technique is introduced to survey the evolving vorticity field on the airfoil. The information about the vorticity convection and the surface vorticity flux over the wing provides a basic understanding regarding the variation of the unsteady lift.