An experimental investigation of oscillating flow in a tapered channel

Oscillating flow in a tapered channel was studied experimentally by observing the deformation of a dye streak within a Plexiglas channel during piston induced, volume-cycled oscillations. The observed steady streaming was compared to theoretical calculations. Both the theoretical and experimental results show bi-directional drift for all frequencies, with characteristics dependent upon the value of the Womersley parameter, α = b (ω/ν) ½ . For large values of α, e.g. α > 10, the fluid near the walls and along the centreline drifted towards the narrow end of the channel, while fluid in an intermediate region drifted towards the wide end of the channel. For small values of α, e.g. α < 5, the fluid drifted towards the narrow end at the wall and the wide end of the channel along the centreline. Applications to mass transport in the lung are discussed.