1408 乱流境界層中に噴出する微小気泡の生成機構について

概要

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When many small bubbles are injected into a liquid turbulent boundary layer, the drag on the wall is reduced noticeably. It is important to clarify the process of bubble formation from air jet because the drag reduction is strongly dependent on the bubble size. In this report, the behavior of airflow was carefully observed near a small orifice on the wall. The orifice diameter d_0 free stream velocity U_∞ and airflow velocity v_0 were varied as d_0=0.2m/s, 0.4mm, U_∞=1∿4m/s and v_0=10&acd60m/s, respectively. When v_0 is quite large, the airflow forms a cylindrical jet which elongates in the free stream direction. The observation by use of high-speed video camera shows that the airflow from the orifice impinges into the separated bubble and coalesces. The cylindrical jet with periodic knots on the liquid-air interface is formed by the repetition of above process.