No vortex in straight flows -- on the eigen-representations of velocity gradient

Xiangyang Xu, Zhiwen Xu, Changxin Tang +2

Velocity gradient is the basis of many vortex recognition methods, such as Q criterion, $\Delta$ criterion, ${\lambda }_2$ criterion, ${\lambda }_{ci}$ criterion and $\Omega$ criterion, etc.. Except the $λ_…