Effects of boundary conditions on downstream vorticity from twin-stage swirlers

PIV experiment and numerical simulation were utilized to study the non-reaction flow field downstream of the single-swirler and the multi-swirler, which had the same twin-stage structure. Velocity fields, vortex structures and variation of vorticity in both cases were compared and analyzed to study the effects of different boundary conditions on vortex structure of twin-stage swirler. The results of PIV experiment and numerical simulation agreed well on the structure and variation of the central vortex vorticity. In the single-swirler case, two couples of corner vortex were formed due to the interaction between the swirl-flow of swirler and walls, and in the multi-swirler case, a vortex located on the boundary between two swirlers called boundary vortex was formed due to the interaction between the swirl-flow of the swirlers. The vortex intensity of the central vortex in the single-swirler case was always smaller than that in the multi-swirler case before the jets from primary holes, specifically, at a distance of 10 mm from the outlet of the swirlers. The results of numerical simulation show that the vortex intensity of the central vortex in the single-swirler case was 92.4% of that in the multi-swirler case, while the results of PIV experimental show that the value was 90.0%. The jets from the primary holes enhanced the vortex intensity of the central vortex, and such effect was more significant in the single-swirler case. The difference of vortex structure located in external fluid under different boundary conditions resulted in the different variation of the central vortex vorticity.