Quasicylindrical description of a swirling light gas jet discharging into a heavier ambient gas

The structure of an axisymmetric swirling gas jet of a light species discharging into an ambient of a heavier gas is analyzed using the quasicylindrical approximation of the compressible flow equations, with the main aim of describing the conditions for the onset of vortex breakdown A self-similar solution valid in the mixing-layer close to the jet exit is found, which is used to start the numerical integration of the parabolic equations For the computations, we consider the particular case of a swirling jet of hydrogen discharging into air We characterize the critical swirl number for vortex breakdown as a function of the coflow velocity of the ambient gas, and compare it to the case of a homogeneous, single-species gas jet, discussing the physical differences found between the cases We also consider the influence of the Mach number on the onset of vortex breakdown, and discuss the results in relation to the incompressible limit, finding that the swirl level for breakdown decreases as the Mach number increases (C) 2010 American Institute of Physics [doi 10 1063/1 3489127]