Two spiral vortex breakdowns in confined swirling flow

Two different scenarios of spiral vortex breakdown are observed experimentally and further investigated numerically in the swirl flow into a conical diffuser. The primary spiral vortex breakdown is observed near the inlet of the conical diffuser in cases of the cone angle beta > 3 degrees. The secondary spiral vortex breakdown occurs at the exit of the cone at beta <= 3 degrees. Also, the coexistence of two spiral vortices is observed. For the first time, we have visualized and explained the reasons of these observations.

Automated summary

Two different scenarios of spiral vortex breakdown are experimentally observed and numerically investigated in a swirl flow into a conical diffuser. The primary spiral vortex breakdown occurs near the inlet of the conical diffuser when the cone angle beta is greater than 3 degrees. The secondary spiral vortex breakdown occurs at the exit of the cone when beta is less than or equal to 3 degrees. Additionally, the coexistence of two spiral vortices is observed, and their reasons are visualized and explained for the first time.