Experimental investigation of vortex breakdown in a coaxial swirling jet with a density difference

► We studied a stable vortex breakdown in a variable-property coaxial swirling jet. ► A model using common nondimensional numbers is proposed to explain the following. ► The height of the stagnation point increases with increasing outer jet velocity. ► The height of the stagnation point is always lower for a denser inner jet. ► The model is fairly successful in explaining the trends observed in our study.