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 operatio nal variables due to the complexity of the flow. For engineering desig n purposes, parametric study is the conventional approach. In this inv estigation, an alternative approach is used. It is demonstrated here t hat the physical insights of the intricate unsteady aerodynamic flow c an be understood from a simple fundamental vorticity balance concept. The test configuration is a stationary two-dimensional NACA 0012 airfo il placed at the static stall angle of 12-degrees in an unsteady free stream. A local circulation measurement technique is introduced to sur vey 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 unstead y lift.