Experimental results of the speed of travel of a disturbance in front of suddenly switched-on and switched-off submerged laminar jets are presented. The results show that the time lag for a switched-off jet is approximately one half the time required for a particle moving in front of a switched on jet to reach a certain distance from the jet nozzle. The time lags for an instantaneous change in the jet intensity is approximately the same as that for switching the whole jet on and off. These experimental data can be used to calculate the switching times of turbulence amplifiers.

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