Flow regimes in the T-jets reactor were studied by planar laser induced fluorescence (PLIF) technique and large-eddy simulation (LES). It was found that four different flow regimes

the separated flow (Re<120)

steady engulfment flow (120 ≤ Re<190)

unsteady engulfment flow (190 ≤ Re ≤ 300) and unsteady symmetric flow (Re>300) displayed in turns with the increase of Reynolds number. In particular

the characteristics of unsteady engulfment regime were investigated by LES. The results showed that eddies periodically merged in the impingement plan and the subsequent merged eddies passed through the chamber which caused self-sustained oscillation in the reactor. The pressure

velocity and vorticity in the impact zone also varied periodically

and the periods were consistent with that of eddy merging in unsteady engulfment regime. This oscillation of eddy merging and propagation is caused by the periodic variation of velocity and pressure in the impingement plane.