Annular swirling flow with S = 0.6

Series of visualization of the instantaneous axial velocity field (outer part) together with the isosurface of the non-positive time-averaged axial velocity field (red bubble right behind the bluff body). An isosurface of the instantaneous pressure field (structure in the center) is indicating the helical vortical structure precessing around the jet axis and emerging recirculating bubble, which are merging with the central recirculation zone while the swirl number increases. Present visualization shows the case for the swirl number S = 0.6