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Roughness effects on separated and reattached open channel turbulent flow

DOI: 10.1615/ICHMT.2012.ProcSevIntSympTurbHeatTransfPal.1810
pages 1770-1781

Afua A. Ampadu-Mintah
Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, R3T 5 V6, Canada

Mark F. Tachie
Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg MB, R3T 5V6 Canada

Martin Agelin-Chaab
Automotive, Mechanical and Manufacturing Engineering Department, University of Ontario Institute of Technology Oshawa, ON, L1H 7K4, Canada

Sinopsis

An experimental study was undertaken to investigate the effects of surface roughness on the mean velocity and higher order turbulence statistics in separated and reattached open channel turbulent flows downstream of a backward facing step (BFS). The BFS was kept hydraulically smooth but the floor downstream of the step was covered with two different roughness elements. In addition to these two rough surfaces, a reference smooth surface was also studied to facilitate the interpretation of roughness effects on the flow characteristics. The depth of the approach open channel flow, the approach freestream velocity and Reynolds number were kept approximately constant for each of the experiments at 66 mm, 0.3 m/s and 19800 respectively to ensure that the boundary layer characteristics of the approach flow are similar in all the three test cases. The results showed that surface roughness significantly reduced reattachment length and turbulence level in the separated region. Two point correlation analyses indicated that in the separated region there is similarity between the smooth wall and the rough wall in the near wall region but in the redevelopment region the data for the smooth wall is more correlated than the rough wall in the near wall region.

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