Convenient visualization method for identifying vortex centers

When a linear parametrization is applied to the cellwise velocity distribution given by a numerical solution, the streamline equations become a set of linear, ordinary differential equations whose solutions can be found quite easily. The analytic expression of the local streamline solutions enables us to identify the focal point of a vortex as well as the centerline of a longitudinal vortex core. The present method identifies the vortex center as a collection of the line segments locally defined in the computational cells. The results of a test calculation as well as practical applications dealing with unsteady vortical flows are shown to examine the present approach. It is demonstrated that the unsteady vortex motions can be conveniently visualized by showing their temporal core positions.