PIV measurements of turbulent flow overlying large, cubic- and hexagonally-packed hemisphere arrays

Taehoon Kim, Gianluca Blois, James L. Best, Kenneth T. Christensen

Research output: Contribution to journalArticlepeer-review


Turbulent flow overlying periodic arrays (cubic- and hexagonally-packed) of large hemispheres was examined experimentally. Flow in the vicinity of the individual roughness elements was successfully examined by conducting particle-image velocimetry measurements in a refractive-index matched flume where the refractive index of the working fluid matched that of the acrylic hemispheres. The spatial structure of flow in the roughness sublayer is spatially heterogeneous and significantly influenced by the topographic pattern of the hemispheres. However, structural coherence was observed outside the roughness sublayer, independent of the measurement location and packing arrangement. Consistent with previous studies, it appears that mean shear near the inflection point of the velocity profile plays an important role in generating high-intensity Reynolds shear stress events and the contribution of roughness-scale energy within the roughness sublayer was apparent in spatial spectra of velocity. In the outer layer, despite the small relative-submergence condition, first- and second- order velocity statistics in all rough-wall conditions showed outer-layer similarity.

Original languageEnglish (US)
Pages (from-to)363-383
Number of pages21
JournalJournal of Hydraulic Research
Issue number2
StatePublished - Feb 23 2020


  • Large roughness
  • PIV measurement
  • outer-layer similarity
  • roughness sublayer
  • small relative submergence
  • turbulent flow

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology


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