  In this paper, a modified normalized Rortex/vortex identification method
named Omega_R is presented to improve the original Omega_R method and cure the
bulging phenomenon on the iso-surfaces caused by the original Omega_R method.
Detailed mathematical explanations and the relationship with the Q criterion
are described. In addition, the new developed formula does not require two
original coordinate rotations, and the calculation is greatly simplified. The
numerical results are demonstrated to show the effectiveness of the new
modified normalized Rortex/vortex identification method.
