An experimental investigation of swirling jets

The ‘plug’ flow emerging from a long rotating tube into a large stationary reservoir has been used in an experimental investigation of centrifugally unstable swirling jets. A moderate Reynolds number, Re\,=\,1000 , was studied extensively, and swirl numbers, S , the ratio of nozzle exit rotating speed to the mean mass axial velocity, were in the range 0–1.1. Four regimes were covered: non-swirling jets with S\,=\,0 , weakly swirling jets in the range 0\,<\,S\,<\,Sc1 , strongly swirling jets before vortex breakdown with Sc1\,<\,S\,<\,Sc2 , and stable vortex breakdown for S\,>\,Sc2 , where Sc1\,=\,0.6 and Sc2\,=\,0.88 .