Flapping characteristics of the self-excited flapping motion of submerged vertical turbulent jet in narrow channels are studied theoretically and experimentally.It is found that the water depth is a most important parameter to the critical jet exit velocity and the jet flapping frequency.The results indicate that the critical jet exit velocity increases with water depth and the jet flapping frequency is inversely proportional to the water depth.Meanwhile,experimental result also shows that the surface disturbance wave changes the frequency of flapping motion,i.e.the flapping frequency locks-in the disturbing frequency when the disturbing frequency is near and less than the natural flapping frequency.
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