New normalized Rortex/vortex identification method

A new vortex identification criterion, named ΩR, is proposed for the normalization of Rortex, using the idea of the Omega method (Ω). ΩR is a normalized function from 0 to 1, which measures the relative rotation strength on the plane perpendicular to the local rotation axis. The advantages of the proposed ΩR method can be summarized as follows: (1) ΩR is from 0 to 1 and can be further used in statistics and correlation analysis as a physical quantity. (2) ΩR can distinguish the rotational vortices from the shear layers, discontinuity structures, and other non-physical structures. (3) ΩR is quite robust and can be always set as 0.52 to capture vortex structures in different cases and at different time steps.