Influences of heat release, blockage ratio and swirl on the recirculation zone behind a bluff body

The recirculation zone created through vortex breakdown mechanisms in swirling flows plays a vital role for aerodynamic stabilisation of turbulent flames in practical combustion systems. This zone interacts with the wake of an upstream bluff body and leads to a complex flow behaviour that depends on the blockage ratio and swirl number. The vortex breakdown bubble merges with the wake at large swirl number or blockage ratio. Although these behaviours were studied well for isothermal flows, the effects of heat release on these flow patterns are not understood sufficiently. In this study, the influences of heat release on this flow structure and their physical mechanisms are explored through a series of large eddy simulations of bluff body stabilised swirling premixed flames. Detailed analyses of the results show that the bubble moves upstream leading to its stronger interaction with the wake in combusting flows which can affect the thermo-acoustic characteristics of the combustor. Comparisons of simulation results with measurements are observed to be good.