  A novel method is proposed to identify vortex boundary and center of rotation
based on tubular surfaces of constant stagnation pressure and minimum of the
stagnation pressure gradient. The method is derived from Crocco's theorem,
which ensures that the gradient of stagnation pressure is orthogonal to both
the velocity and vorticity vectors. The method is Galilean invariant, requires
little processing and is robust. It enables visualization of complex turbulent
flows and provides a physically consistent definition of vortex boundaries for
quantitative analyses. This vortex boundary is a material surface that is
representative of the kinematics of the flow by construction, constitutes a
vortex tube, ensures conservation of circulation in the inviscid limit and
provides a unique relation to the conservation of momentum equations and vortex
loads.
