An electrochemical study of flow instability on a rotating disk

Abstract

Data for the fluctuating mass-transfer coefficient to point electrodes on the surface of a rotating disk are presented for transition and turbulent flow, along with analysis of the energy spectrum. The results corroborate previous evidence of standing vortices on the surface in the transition region. It is shown that the electrochemical method gives a more sensitive probe of flow instabilities than has been possible previously; the transition region is found to be wider than has been previously thought to be and lies between roughlyRe= 1·7 × 105and 3·5 × 105, whereRe=r2ω/vis the Reynolds number, ω being the angular velocity of the disk (in rad/s) andvthe kinematic viscosity. As the Reynolds number is increased, the stationary vortices in the transition region propagate primarily with a frequency matching that of the disk speed. After a peak energy has been reached atRe= 2·6 × 105, the vortices break down into a fully developed turbulent flow.