Large eddy simulation of flows after a bluff body: Coherent structures and mixing properties

• Large eddy simulation is performed to the jet flow in a coflow after bluff body.
• Three dimensional instantaneous flow structures are investigated using Q function method.
• Coherent structures are obtained using phase average method introduced by Hussain (1986) based on a triple decomposition and their influences on momentum and scalar transport flux are discussed.

This paper performs large eddy simulations (LES) to investigate coherent structures in the flows after the Sydney bluff-body burner, a circular bluff body with an orifice at its center. The simulations are validated by comparison to existing experimental data. The Q function method is used to visualize the instantaneous vortex structures. Three kinds of structures are found, a cylindrical shell structure in the outer shear layer, a ring structure and some hairpin-like structures in the inner shear layer. An eduction scheme is employed to investigate the coherent structures in this flow. Some large streaks constituted by counter-rotating vortices are found in the outer shear layer and some well-organized strong structures are found in the inner shear layer. Finally, the influences of coherent structures on scalar mixing are studied and it is shown that scalar in the recirculation region is transported outward by coherent structures.