| The persistence theory of turbulence postulates that the stationarity of a vortex near an interface, be it solid or fluid, is a determiner of the turbulent flux rates at the interface. The present work tabulates and explores two dimensional vortex flow configurations that exhibit kinematic stationary conditions. An analytical method for deriving potential and streamfunctions from complex potentials is demonstrated and employed extensively. We unexpectedly find that stationary vortex arrays may play the role of the underlying attractors for instability and growth mechanisms exhibited by the large scale coherent two dimensional structures of free turbulence, e.g. in the shear layer. Also we report on an experimental study that exploits the stationarity property of von Karman's vortex street to embed an array of stationary vortices in a fully turbulent boundary layer. The experiments demonstrate that the persistent regime of turbulent fluxes can be successfully achieved at a solid interface through the use of such stationary vortices. |
