1038 TRANSITIONAL REYNOLDS NUMBER IN SUBMERGED MACRO- AND MICROJETS

抄録

The current research is aimed at experimental investigation of round and plane submerged macro- and microjets. The measurements were carried out by two methods: Particle Image Velocimetry (PIV) and measurements with the use of hot-wire anemometer. At the first stage there were the experiments on flow visualization in microjets by means of the PIV system. The axisymmetrical microjets were formed with the help of round metal channels with diameter d=500-8000 μm and length of 100 d. The plane channel was formed by two glass plates of 16x70 mm; its height was b =600 μm. The range of Reynolds numbers was Re=Ud/ν=200-6000. It is accepted that submerged jets are significantly unstable, therefore, the Re numbers of laminar-turbulent transition are not higher than 10. However, according to visualization, the jet stays laminar even at Re numbers of several hundreds. This is typical both to microjets and macrojets. At the next stage, according to visualizations and anemometer measurements, the coordinate of laminarturbulent transition L in the submerged jets was determined at variations of Re number. Our experimental data was compared with data of other authors. The length of the laminar zone in the round jets is twice as large as in the plane jets. Our experiments for the plane jet agree with data of Gau C. et. al. 2009 (nozzle height is 50-360 μm). Data for the round jets of different authors diverge significantly.