Abstract: Sever al methods for visualizing the flow structures by using sectional data were compar ed and analyzed tofind the r eason why sectional str eamlines cannot describe vor tices structures corr ectly. Consequent ly, a new conceptof sectional spin vector defined by the vector product of Lamb vectos and normal vector of the section is proposed.Compar ing with other met hods, the visualized structur es of flow field described by the spin vector ismore corr ect because the sectional cross-lines of the Lamb sur face and the observational plane as described by the suggested methoddo not distort the visualized flow phenomena even the observational plane is not proper ly chosen.

Key words: flow visualization, Lamb vector, sectional spin vector, 3-D vortex structure