Behavior of Turbulent Slugs in a Transient Pipe Flow

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The generation and propagation of turbulent slugs in a circular pipe were studied under transient flow conditions. The Reynolds number chosen for the final steady state was above the critical Reynolds number of the experimental apparatus. A turbulent slug was initiated about 10 diameters downstream of the entrance, preceded by unstable waves with a frequency very similar to that of the Tollmien-Schlichting wave. After the passage of the first slug, many slugs appeared in the region of x/D≒14∼40, where x was the axial distance and D was the pipe diameter. The axial propagation velocities of the leading and trailing edges of the first slug were determined and compared with those of slugs in steady pipe flows. Velocity distributions inside and outside the slug were examined.