Two spiral vortex breakdowns in confined swirling flow

Abstract

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 β>3°. The secondary spiral vortex breakdown occurs at the exit of the cone at β≤3°. Also, the coexistence of two spiral vortices is observed. For the first time, we have visualized and explained the reasons of these observations.