EFFECT OF UNSTEADY FORCING ON THE SINUSOIDAL INSTABILITY OF VORTEX WAKES.
An analytical model of the vortex wake instability subject to forcing by unsteady lift fluctuations has been developed. These lift fluctuations can be caused either by variations in angle of attack or by flying through atmospheric turbulence. A simple procedure is provided to estimate the time at which contact occurs between the two wake vortices as a function of certain characteristics of the forcing inputs. The behavior of the instability is somewhat altered by these forcing terms. In particular, it was found that contact between vortices can occur at much shorter wavelengths than predicted for the unforced case.