<abstract xmlns="http://www.w3.org/1999/xhtml"><p> Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.</p></abstract>

Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Department of Civil Engineering, IIT Kharagpur, Kharagpur, 721302,

Department of Mechanical Engineering, University of Windsor, Windsor, ON, N9B 3P4,

Department of Civil and Environmental Engineering, University of Windsor, Windsor, ON, N9B 3P4,

Journal of Hydrology and Hydromechanics

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of...

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Published Online: Dec 08, 2016

Page range: 35 - 48

Received: Nov 26, 2015

Accepted: May 20, 2016

DOI: https://doi.org/10.1515/johh-2016-0044

Keywords
Turbulence, Open channel, Bedforms, Higher-order moments, PIV, Quadrant analysis

© 2016

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Published Online: Dec 08, 2016

Page range: 35 - 48

Received: Nov 26, 2015

Accepted: May 20, 2016

DOI: https://doi.org/10.1515/johh-2016-0044

KeywordsTurbulence, Open channel, Bedforms, Higher-order moments, PIV, Quadrant analysis

© 2016

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Keywords
Turbulence, Open channel, Bedforms, Higher-order moments, PIV, Quadrant analysis