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Fourth International Symposium on Turbulence and Shear Flow Phenomena
June, 27-29, 2005, Marriot Hotel, Williamsburg, Virginia, USA

DOI: 10.1615/TSFP4

RESPONSE OF OPEN CHANNEL FLOW TO A SUDDEN CHANGE FROM ROUGH TO SMOOTH SURFACE

pages 171-176
DOI: 10.1615/TSFP4.290
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RÉSUMÉ

Measurements of mean velocity and higher order turbulence statistics are presented for the study of flow response and relaxation in the presence of a sudden change in surface geometry from rough to smooth surface in an open channel. The rough surface was made up of spherical ribs. The ribs were constructed using spherical glass beads of diameter D (or k) = 12.5 mm joined together transversely across the width of the channel. Two types of roughness, a d-type and an intermediate-type, having pitch to height ratio of 2 and 4, respectively, were used in the study. For the rough wall data obtained on the crest of the rib, the intermediate-types indicated a higher roughness effect. After the sudden change, mean velocity profiles relax rapidly to a smooth wall type profile in the near wall region. After the sudden change in roughness, the mean velocity rapidly assumed a smooth-wall-like behaviour in the near wall region. The relaxation to the smooth-wall behaviour was rather slow for the higher order turbulence statistics near the wall. In the outer region, the mean and turbulence quantities showed that the flow is still relaxing toward a smooth wall type flow.

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