Abstract
The paper presents the results of an experimental study of the hydrodynamics of jets flowing from long tubes at low Reynolds numbers. The main attention in the research is given to the mechanism of interaction between pipe and jet instability, which results in a vortical motion in several spatial regions. In the experiments we used Hilbert-visualization, high-speed visualization, and measurements with a hot-wire anemometer. The subsonic gas jet flows into the air space from a long tube with a diameter of 2, 3.2, and 5 mm within the Reynolds number range of 200-6700. Air and Freon-22 were used as the working gases. The critical pipe Reynolds numbers are characterized by the mechanism of a two-stage instability caused by the formation of turbulent spots (puff) inside the tube and generation of vortex structures in the jet mixing layer. These organized structures (puff) exert a strong influence on the free jet flow destroying the laminar flow part. The obtained data make it possible to consider in detail the evolution of turbulent spots along the distance downstream, while the spots are generated in a cylindrical tube due to the laminar-turbulent transition.
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