Developing oscillatory flow in a strongly curved tube

Laser Doppler velocity measurements were performed on developing oscillatory flow in a strongly curved tube, in which a curvature ratio, a/R (defined as the ratio of the tube radius to the radius of curvature) of 1/2 was achieved. At the Womersley number of 4.5, curvature effects enhanced the secondary flow and maximum secondary flow velocity increased to 60% of the amplitude of the cross-sectional averaged axial velocity in the curved tube of a/R = 1/2 . On the other hand, for a larger Womersley number (=18), the velocity at the edge of the boundary layer at the inner wall significantly increased just downstream of the entrance due to the formation of potential vortex, which is strongly dependent on large curvature effect.