An Experimental Investigation of Transition of a Plane Poiseuille Flow

Abstract

The transition process of laminar flow between parallel plates is investigated experimentally. This problem has recently gained much attention with several reported works; however, the maximum transition Reynolds number reported has been approximately 3000 (based on average velocity and channel height) whereas the theoretical critical Reynolds number is 7700. Primary emphasis in this work is on approaching the theoretical limit in an experimental facility. A high aspect ratio (70 to 1) channel was used with air as the fluid. As the disturbance level at the entrance to the parallel plate section was reduced the transition Reynolds number increased monotonically. At a disturbance level of 0.3 percent the transition Reynolds number was 6700. Near transition small nearly sinusoidal waves in the critical shear layer were observed. The frequency of the waves was approximately 70 hertz, close to the frequency associated with the Tollmien-Schlichting waves of the critical point of linear theory. Sinusoidal waves preceded a turbulent burst which possessed an essentially plane front as it traveled downstream. As the Reynolds number was increased the bursting rate increased and the flow eventually became completely turbulent.