Behavior of oscillatory tube flow at liquid-gas interfaces

Abstract

This is the published version of the paper.This version of the publication may differ from the final published version. Oscillatory flow in a long tube is characterized by an annular axial velocity profile far away from the boundaries for which an analytical solution exists. The radial velocity component is zero. Near the entrance or free surface region, this analytic solution does not hold due to the boundary conditions. Herein, the flow behavior at a liquid-gas as well as liquid-wall interface is investigated in detail by means of flow visualization measurements and Particle Image Velocimetry. The results suggest an additional radial velocity component due to the influence of the boundary. An investigation of the phase locked flow depicts the generation of steady streaming below the free surface which could be identified by vortex rings. Their shape and velocities vary according to the boundary conditions. For low frequencies, the streaming patterns are similar for cases with liquid-gas and liquid-wall interface denoting that the surface tension does not play a role for these cases. The oscillatory amplitude dominates streaming strength. As the Womersley number increases the free surface becomes unstable and Faraday waves occur which are further analysed here. This instability interacts with the steady streaming patterns which causes a change in shape and increases the streaming strength. C 2014 AIP Publishing LLC. [http://dx Permanent repository link: