Numerical study of hysteresis in annular swirling jets with a stepped-conical nozzle

This study investigates the experimentally observed hysteresis in the mean flow field of an annular swirling jet with a stepped-conical nozzle. The flow is simulated using the Reynolds-averaged Navier-Stokes (RANS) approach for incompressible flow with a k-epsilon and a Reynolds stress transport (RSTM) turbulence model. Four different flow structures are observed depending on the swirl number: 'closed jet flow', 'open jet flow low swirl', 'open jet flow high swirl' and 'coanda jet flow'. These flow patterns change with varying swirl number and hysteresis at low and intermediate swirl numbers is revealed when increasing and subsequently decreasing the swirl. The influence of the inlet velocity profile on the transitional swirl numbers is investigated. When comparing computational fluid dynamics with experiments, the results show that both turbulence models predict the four different flow structures and the associated hysteresis and multiple solutions at low and intermediate swirl numbers. Therefore, a good agreement exists between experiments and numerics. Copyright (C) 2006 John Wiley & Sons, Ltd.