Abo Bibliothek: Guest
Ninth International Symposium on Turbulence and Shear Flow Phenomena
June 30 - July 3, 2015, University of Melbourne, Australia

DOI: 10.1615/TSFP9

SKIN-FRICTION BEHAVIOR IN THE TRANSITIONALLY-ROUGH REGIME

pages 157-162
DOI: 10.1615/TSFP9.270
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ABSTRAKT

Results of an experimental investigation of the skin friction for a range of rough surfaces in fully-developed, turbulent channel flow are presented. The fifteen surfaces were generated by grit blasting with various types and sizes of media. The Reynolds number (Rem) for the experiments based on the bulk mean velocity and the channel height spanned from 10,000 − 300,000. The root-mean-square roughness height (krms) is shown to be most strongly correlated with the equivalent sand roughness height (ks) for the grit-blasted surfaces. The shape of the roughness function (ΔU+) for all of these surfaces shows self-similarity. The roughness function displays inflectional behavior in the transitionally-rough regime in a similar manner to the results of Nikuradse for uniform sand. The equivalent sand grain roughness height can be predicted using krms and the skewness (Sk) of the probability density function of the roughness amplitude. A longwavelength filtering procedure based on the Taylor microscale (λ) of the roughness is presented, and it is recommended that roughness profiles be filtered at a scale of at least 50λ.

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