Fig. 3. The test of four vortex identification criteria. Data at 0.25T, when the vortical system was most intricate, were tested. The dimensionless values of the iso-surfaces (the red regions) of ||, , Q and ₂ are 0.22, 0.00015, 0.09 and 0.04, respectively. The values of ||, and Q are normalized by their maxima (>0), whereas the value of ₂ is normalized by the minimum (<0). The blue plate is the model wing.