An Experimental Study on Unsteady Jets: Observation on the Behaviour of the Tip of Unsteady Region and the Vortex Pair by Means of Flow Visualization

This paper concerns transient motions produced by the jet suddenly injected into still water, and by instantaneous change of flow rate of the steady jet from one value to another. The purpose of this paper is to make clear the effect of the length of parallel section of the nozzle upon the flow characteristic of unsteady jets. The behaviour of the tip of unsteady region and the vortex pair are visualized by means of the electrolytic precipitation method and the hydrogen bubble method. It is found that the tip of unsteady region and the vortex pair move downstream faster as the parallel part of the nozzle is longer. We also found that the tip velocity of unsteady region first increases, then decreases and at last becomes constant. In addition, in the case of the long part of nozzle, the characteristic of the transport speed of vortex pair is different from that in the other experiment conditions.