Simulation of the Nonreacting Flow in a Bluff-Body Burner; Effect of the Diameter Ratio

Axisymmetric vortex simulation is used to study the unsteady dynamics of the flowfield generated by the interaction between two concentric jets initially separated by a thick bluff-body. The computational scheme treats convective transport in a Lagrangian sense by discretizing the vorticity into a number of finite-area vortex ring elements which move along particle trajectories during each convective substep, thus reducing the numerical diffusion and allowing simulations at high Reynolds number. In this paper, investigation is focused on the time-dependent dynamics and the effect of the diameter ratio across the bluff-body on the wake flow. In both cases simulated, the dynamics is governed by the shedding of large vortex eddies from the inner and outer sides of the bluff-body. Mixing between the two streams is enhanced by the merging of these eddies downstream the bluff-body and the formation of composite structures. We find that the frequency of shedding, the level of fluctuations and the degree of organization are strongly dependent on the diameter ratio. The fluctuation associated with this shedding increases as the diameter ratio becomes larger. The origin and mechanism of shedding in each case are determined from the results.