Transition to turbulence and slow dynamics in von Karman swirling flow

The transition from laminar to turbulent flows is characterized by the Reynolds number Re, a non-dimensional number resulting from the ratio of inertial and viscous terms in the Navier-Stokes equations. A lot of efforts has been made to measure and predict the onset of turbulence in various flows of different geometrical configurations characterized mostly by smooth boundaries, i.e. by  viscous forcing. During the last two decades von Karman swirling flow between two counter-rotating disks became one of the main experimental closed flow setups to study the problems of the transition to turbulence and characterization of  the flow before the transition and fully developed turbulence in various fluids due to an easy control of the main parameters, a possibility to use numerous experimental techniques to measure various flow physical characteristics and fields and
comparatively easiness to achieve very high Re. This setup also allows to study the influence of viscous versus inertial flow forcing on the transition to turbulence and on flow properties before and after the transition. The swirling flow driven by unbounded smooth disk was introduced by von Karman in 1921 and extensively studied ever since and his exact solution provides the friction coefficient for a disk wetted on both sides as Cf = 1.985/√Re. Since then numerous theories and numerical simualtions and very limited number of experiments were conducted.  First, it is imprortant to verify with better accuracy the expression for Cf together with velocity field measurements to test which solution from several predicted realizes  and corresponds to  Cf. These studies will be conducted for fluids in large range of viscosities to test the similarity law.  The same reaserch will extended to swirling flow driven inertially by the bladed disks, concentrating in particular on averification of  the similarity law for fluids with viscosity varied in a wide range of values.