まっすぐな円管内の乱流旋回流の特性 : 広い旋回強度範囲における旋回の減衰(流体工学,流体機械)

概要

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The swirl decay mechanisms are described for a wide range of swirl strengths in a straight pipe made of Plexiglass and 154.5mm in inner diameter and 9500mm long. Flow measurements using a cylindrical Pitot tube and a hot-wire anemometer are performed at a Reynolds number of 10^5, which is based on the inner diameter of the tube and the axial mean velocity. A guide-vane swirl generator, with guide-vane angles of 60, 45, 30, 5 and 0 degrees, is employed. As a result, the swirl number and the swirling angle neighboring the pipe wall exponentially decrease downstream. Axial velocity, which decreases in the central domain at a high swirl strength, gradually recovers downstream simultaneously with the swirl decay. The combined vortex formed upstream changes to a forced vortex far downstream. It is confirmed that the local angular momentum, which gradually changes in the central domain, exponentially decreases downstream neighboring the pipe wall. The conjectured swirl decay mechanisms in a straight pipe are as follows. First, the swirl decay mainly occurs in an annular region at a high swirl strength. Second, it occurs in the central domain at a medium swirl strength. Third, it occurs in the whole pipe cross-sectional area at a very low swirl strength.
2009-06-25