The paper 'A new way to describe the transition characteristics of a rotating-disk boundary-layer flow' by Shintaro Imayama, P. Henrik Alfredsson, and R. J. Lingwood has been the 2nd most downloaded Physics of Fluids paper during March 2012 (link).
A new method of graphically representing the transition stages of a rotating-disk flow is presented. The probability density function contour map of the fluctuating azimuthal disturbance velocity is used to show the characteristics of the boundary-layer flow over the rotating disk as a function of Reynolds numbers. Compared with the variation of the disturbance amplitude (rms) or spectral distribution, this map more clearly shows the changing flow characteristics through the laminar, transitional, and turbulent regions. This method may also be useful to characterize the different stages in the transition process not only for the rotating-disk flow but also for other flows.