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Research paper

Roughness effects on near-wall turbulence modelling for open-channel flows

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Pages 648-661 | Received 09 Oct 2016, Accepted 12 Oct 2017, Published online: 15 Mar 2018
 

ABSTRACT

Accurate modelling of near-wall turbulence influenced by roughness is crucial in hydraulic engineering. This study presents modifications on the k-ϵ turbulence model for open-channel flows over rough bed based on reliable particle image velocimetry data. Experiments have been conducted for different roughness heights. Some near-wall turbulence characteristics (e.g. bursting events) are identified and the profiles of mean streamwise velocity, Reynolds shear stress and turbulence intensities are validated with direct numerical simulation data. Experimental results confirm that the coefficient cμ involved in the k-ϵ model varies with roughness Reynolds number in outer region, and with both and y+ (normalized distance from the wall) in near-wall region. A new damping function is reconstructed, and the profile of turbulent kinetic energy close to the wall is analytically obtained. The present modifications accounting for wall roughness effects are further implemented into the k-ϵ model and validation shows that the prediction accuracy for the near-wall flow has been improved.

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China [grant 51578062] and the Science and Technology Research and Development Projects of China Railway [grant 2014G009-H].

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