Geometric models with respective changes of plug radius at lobe exit and plug length in the lobed forced mixing exhaust system were established.Then these models were numerically simulated based on Navier-Stokes equations.The results show that when plug length is constant

the thermal mixing efficiency increases at first and then declines with plug radius at the lobe exit augmenting

and when ratio of plug radius at lobe exit to lobe height is equal to 0.55

the lobed mixing exhaust system has the biggest thermal mixing efficiency at the nozzle exit among the models researched.Generally speaking

the total pressure recovery coefficient declines as radius increases.Moreover

the thrust coefficient at the nozzle exit firstly increases and then decreases sharply.When plug radius at lobe exit keeps constant

with plug length rising

the thermal mixing efficiency and total pressure recovery coefficient vary little and the thrust coefficient at the nozzle exit augments quickly in the beginning and then declines slowly.