Key points are not available for this paper at this time.
Vortex structure is characterized in terms of the magnitude of the vorticity and strain rate. High vorticity with relatively low strain rate represents the vortex tube, and high vorticity with comparable strain rate the vortex sheet. The regions of high Laplacian of pressure and of high strain rate also represent the tubelike and sheetlike structures, respectively.
Tanaka et al. (Wed,) studied this question.