Stability experiments in the flow over a rotating disk

TLDR: In this article, an experimental study of the transitional flow over a flat disk rotating in quiescent ambient air has been conducted using digitized hot-wire data, the axes of the stationary spiral vortices, which are the primary instability mechanisms for the disk flow, have been mapped out in terms of both spatial coordinates and velocity fluctuations.

Abstract: An experimental study of the transitional flow over a flat disk rotating in quiescent ambient air has been conducted. Using digitized hot-wire data, the axes of the stationary spiral vortices, which are the primary instability mechanisms for the disk flow, have been mapped out in terms of both spatial coordinates and velocity fluctuations. Data are presented for a clean disk and a disk with a single, isolated roughness element. The data show that the spiral vortices are generated at discrete roughness disturbance sites on the disk and that they propagate and grow as wave packets. The familiar vortex pattern of 30 or so vortices results only when these wave packets have merged and filled the entire circumference. The appearance of stationary, secondary instabilities prior to turbulent breakdown has also been observed.