A LES Study On Methane/Air Mixture Flashback In An Axial Swirler

Lean premix combustion is the most promising way to reduce NOx emission in gas turbine combustors. In lean premixed combustion, fuel and air is mixed before ignition. This way leads to lots of problems and one of them is flashback. Axial swirlers are widely used in gas turbine combustors for fuel-air mixing and flame stabilizing. The flashback characteristic of an axial swirler was investigated by LES method.First, the simulation method was validated by comparing the numerical results with the experiment data of a typical swirl stabilized flame.Flashback in the axial swirler was decomposed into two parts:the flashback in an annular channel and the flashback in cascade passages. The method to induce flashback in the annular channel was to reduce the inlet velocity. After dropping the velocity, flashback occurred in both cases of swirl number unchanged and swirl number doubled. Furthermore, a CIVB (combustion induced vortex breakdown) phenomenon was observed in the case with doubled swirl number.The study on cascade passages included two parts:single channel and multi-channel based on which the study of flame propagation was carried out after forced ignition. The results in the single channel shown that after ignition near the suction surface, the flame front propagated along the recirculation zone and held at the separation point of the suction surface; after ignition near the pressure surface, the flame was blown downstream and it could spread to the suction surface and stayed there through the trailing edge of the vane or the inner wall of the channel.The results in the multi-channel shown that after ignition near the suction surface, the behavior of flame propagation was similar to that in the single channel. After ignition near the pressure surface, flame front spread in two directions both along and against the swirl rotating. In the direction along the swirl rotation, the flame also spread upstream along the wake of each vane and held at the suction surface. But in the direction against the swirl rotation, flame front had not been observed to spread further after spreading to the suction surface of the original ignition vane.