Axis switching in impinging premixed methane-air flame jets

Axis switching in non-circular tube burner flame jets is studied. Experimental data of heat flux is obtained for square and rectangular burners of different aspect ratios: 1, 1.55, 2.1 and 3.73. A three dimensional CFD simulation is carried out to explain the phenomenon of axis switching in premixed flame jets. From the CFD simulations it is observed that the vortices formed near the corner of the tube exit are responsible for the axis switching phenomenon. These vortices control the spreading (in a preferential manner) of the flame jet along the tube axis. This preferential spreading of the flame jet is responsible for switching of contours of heat flux on the impingement plate. Furthermore, for the rectangular burner, elliptical lobes of heat flux distribution on the impingement plate are observed and this is again attributed to vortex structures.