Off-axis PTV for 3-D visualization of rotating columnar flows

A new simple optical method for visualizing flow structures generated in a rotating flow is presented. The method consists of planar PTV with sheet illumination slightly offset to the rotation axis and a geometric reconstruction of velocity vector field under the assumption of azimuthal periodicity. Two types of columnar flows intrinsically associated with rotating flows are investigated with the method. The two types of flow are a local columnar wake induced behind a moving sphere, and an asymmetrically precessing Taylor Column created below a spinning disk. By means of this new technique we obtain the first quantitative visualization of the columnar wake and the three-dimensional structure of the Taylor Column.