The flow characteristics of the jet in a sonic oscillator are mainly determined by its geometrical size. The effects of geometrical size were studied by experiments and numerical simulation.The conclusions were as follows:(1)The switch cycle of the jet was proportional to the controlling tube length and approximately equal to the time that sonic wave passed through the controlling tube;(2)When the controlling tube was too long

too wide or too narrow

the jet would not oscillate.The range of the controlling tube length which caused jet oscillation became smaller with narrowing controlling tube;(3)If the wall-offset or wedge-distance was too small

the jet could not attach the wall.In addition

their effects were correlative.When the wedge became nearer to the nozzle

the smallest wall-offset that could induce jet oscillation increased.