Aerodynamics of bluff body stabilized confined turbulent premixed flames

Recirculation-zone structure and turbulence properties of methane-air mixtures downstream of several conical flameholders were measured using LDA. These tests employed different blockage ratios (13 and 25 percent), cone angles (30, 45, 60, and 90 degrees), equivalence ratios (0.56, 0.65, 0.8, and 0.9), mean annular velocities (10, 15, and 20 m/s), and approach turbulence levels (2, 17, and 22 percent). Increasing the blockage ratio and cone angle affects the recirculation zone size and shape only slightly. Also, these parameters increased the shear stress and turbulent kinetic energy (TKE) moderately. Increasing the equivalence ratio or approach turbulence intensity produced a recirculation-zone shape very similar to that found in the cold flow. TKE decreased due to turbulent dilatation produced by increased heat release. These observations are discussed from the viewpoint of their importance to practical design and combustion modeling.