Relaminarization of Pulsatile Turbulent Flow in a Rectangular Duct

抄録

Experiments on the behaviour of turbulent slugs and relaminarization in pulsatile flows are made using four ducts with different aspect ratios. When acceleration is relatively low, the propagation characteristics of a slug is qualitatively similar to that of a steady duct flow. For example, the propagation speed of the leading edge of the slug is larger than that of the trailing edge. In such a case relaminarization of low is controlled mainly by viscous dissipation. Meanwhile, when acceleration is relatively high, the disappearance and the following appearance of turbulent slugs are seen at fixed phases in a cycle and these phases hardly change in the downstream direction. This phenomenon is not inferable from the knowledge of steady duct flows. The relaminarization under the influence of such an acceleration is controlled mainly by acceleration itself and the limit under which relaminarization occurs is described by an acceleration parameter k first introduced about steady accelerating boundary layer flows. Its critical value agrees well with that obtained for steady accelerating flows.