# Measurements of turbulence characteristics in an open-channel flow over a transitionally-rough bed using particle image velocimetry

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DOI: 10.1007/s00348-006-0201-2

- Cite this article as:
- Bigillon, F., Niño, Y. & Garcia, M.H. Exp Fluids (2006) 41: 857. doi:10.1007/s00348-006-0201-2

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## Abstract

The particle image velocimetry technique was used to measure characteristics of a turbulent flow over a transitionally-rough fixed bed in an open-channel flow. These conditions are typical of flows encountered in sediment transport problems. Measurements obtained with this technique were used to investigate the distributions of velocities, turbulence intensities, Reynolds stress, and third- and fourth-order moments in a region above *y*^{+} = 10. The present results are in good agreement to those previously obtained on smooth walls and provide further evidence that PIV can be applied successfully to investigate turbulence in open-channel flows over a rough bed.

### List of symbols

*D*_{v},*D*_{u}turbulent diffusion coefficients in streamwise and wall-normal directions

*F*_{k}vertical flux of turbulent kinetic energy

*F*_{u},*F*_{v}flatness factors for streamwise and wall-normal velocity components

*k*_{s}roughness height (m)

*k*_{s}^{+}roughness Reynolds number,

*u*_{*}*k*_{s}/ν*Re*Reynolds number,

*Uh*/ν*Re*_{*}Reynolds number,

*u*_{*}*h*/ν*S*channel slope (m/m)

*S*_{u},*S*_{v}skewness factors for the streamwise and wall-normal velocity components

*u*mean streamwise velocity (m/s)

*u*_{*}shear velocity (m/s)

*u*^{+}dimensionless velocity,

*u*/*u*_{*}*u*′,*v*′,*w*′velocity fluctuation in streamwise, wall-normal and transverse directions

*u*_{rms},*v*_{rms}velocity standard deviation in streamwise and wall-normal directions

*u*_{rms}^{+}turbulence intensity in streamwise direction, \({u_{\rm rms}}\mathord{\left/ {\vphantom {{u_{\rm rms}} {u_\ast}}} \right.\kern-\nulldelimiterspace} {u_\ast }\)

*v*_{rms}^{+}turbulence intensity in wall-normal directions, \({v_{\rm rms}} \mathord{\left/ {\vphantom {{v_{\rm rms}} {u_\ast}}} \right.\kern-\nulldelimiterspace} {u_\ast}\)

- −〈
*u*^{+}*v*^{+}〉 dimensionless Reynolds shear stress, \(-\overline {u'v'}/u_\ast ^2\)

*y*^{+}dimensionless wall-normal axis,

*yu*_{*}/ν- Δ
*U*^{+} shift in the log-law due to roughness