Diagnostics of spatial structure of vortex multiplets in a swirl flow

Results on investigation of vortex unstable breakdown are presented. The structure of vortex multiplets was visualized in a vertical cylindrical container made of transparent organic glass of the optic quality with the inner diameter of 288 mm and rotating upper lid. Visualization was performed for different heights of this cylinder. The working liquid was 80-percent water-glycerin mixture, and small air bubbles were used as the tracers. The lid was rotated with a constant angular velocity under the studied conditions, and air was accumulated in the zones of decreased pressure on axes of vortices. Visualization of flow structure for unstable swirl flows and cylinder aspect ratios from 3.2 to 5.5 allowed first identification of these regimes as multispiral breakdowns with formation of helical-like vortex duplets, triplets and quadruplets.