The twodimensionalparticle image velocimetry (2D-PIV) planar structure was utilized to measure the flow field of different tripleswirlers under the same inlet condition

helping to analyze the effects of outer swirl number on flow characteristics. The experimental results show that: the swirl intensity of outer swirler is not the critical factor for the formation of central toroidal recirculation zone (CTRZ); the increment of CTRZ length

recirculated mass flowrate ratio

and the decrement of maximum recirculated velocity correspond to the increment of outer swirl number

as the cores of the vortexes move upward and outward; the shape of CTRZ is affected by both outer and inner swirl numbers

and an obvious CTRZ tail can be obtained for swirler with higher outer swirl number; a higher turbulence intensity of the flow generated by tripleswirlers with lower outer swirl number occurs near the swirler exit.