### Abstract

A series of experiments was undertaken to assess fully rough turbulent subcritical flow over two-dimensional transverse repeated-rib roughness of varying spacing lambda/h = I - 16 (roughness spacing/height ratio), with h/H = 0.09 (roughness height/flow depth). Each of the 11 experiments involved centerline measurements of three-dimensional velocity vectors, water surface profiles, and bed pressures and forces. The structure of flow over rib roughness consists of a pair of principal vortices of opposite sign set up by the ribs. These vortices are superimposed on an overall double- (time and space)-averaged velocity profile that is (quasi-) logarithmic above roughness tops, and that below roughness tops changes with increasing rib spacing from exponential (lambda/h < 10) to linear (lambda/h >= 10) to logarithmic (lambda/h >> 10). The measured double-averaged velocity profiles are parameterized herein, and double-averaged Reynolds and form-induced stress profiles and trends are also identified. Maximum drag due to wall roughness is found to occur for lambda/h approximate to 8. The experimentally determined momentum balance, including effects of secondary currents and flow acceleration, is found to agree well with theoretical expectations. It is shown that the knowledge of the effects of form-induced stresses, secondary currents, and flow nonuniformity may be particularly important for describing and modeling flows over roughness elements.

Original language | English |
---|---|

Pages (from-to) | 194-204 |

Number of pages | 11 |

Journal | Journal of Engineering Mechanics |

Volume | 133 |

Issue number | 2 |

DOIs | |

Publication status | Published - Feb 2007 |

### Keywords

- turbulent flow
- boundary layers
- bed roughness
- velocity profile
- fluid dynamics
- spatial analysis
- boundary-layers
- channel flow
- rough-bed
- wall
- velocity
- resistance
- simulation

### Cite this

*Journal of Engineering Mechanics*,

*133*(2), 194-204. https://doi.org/10.1061/(ASCE)0733-9399(2007)133:2(194)

**Spatially Averaged Turbulent Flow over Square Ribs.** / Coleman, S. E.; Nikora, Vladimir Ivanovich; McLean, S. R.; Schlicke, E.

Research output: Contribution to journal › Article

*Journal of Engineering Mechanics*, vol. 133, no. 2, pp. 194-204. https://doi.org/10.1061/(ASCE)0733-9399(2007)133:2(194)

}

TY - JOUR

T1 - Spatially Averaged Turbulent Flow over Square Ribs

AU - Coleman, S. E.

AU - Nikora, Vladimir Ivanovich

AU - McLean, S. R.

AU - Schlicke, E.

PY - 2007/2

Y1 - 2007/2

N2 - A series of experiments was undertaken to assess fully rough turbulent subcritical flow over two-dimensional transverse repeated-rib roughness of varying spacing lambda/h = I - 16 (roughness spacing/height ratio), with h/H = 0.09 (roughness height/flow depth). Each of the 11 experiments involved centerline measurements of three-dimensional velocity vectors, water surface profiles, and bed pressures and forces. The structure of flow over rib roughness consists of a pair of principal vortices of opposite sign set up by the ribs. These vortices are superimposed on an overall double- (time and space)-averaged velocity profile that is (quasi-) logarithmic above roughness tops, and that below roughness tops changes with increasing rib spacing from exponential (lambda/h < 10) to linear (lambda/h >= 10) to logarithmic (lambda/h >> 10). The measured double-averaged velocity profiles are parameterized herein, and double-averaged Reynolds and form-induced stress profiles and trends are also identified. Maximum drag due to wall roughness is found to occur for lambda/h approximate to 8. The experimentally determined momentum balance, including effects of secondary currents and flow acceleration, is found to agree well with theoretical expectations. It is shown that the knowledge of the effects of form-induced stresses, secondary currents, and flow nonuniformity may be particularly important for describing and modeling flows over roughness elements.

AB - A series of experiments was undertaken to assess fully rough turbulent subcritical flow over two-dimensional transverse repeated-rib roughness of varying spacing lambda/h = I - 16 (roughness spacing/height ratio), with h/H = 0.09 (roughness height/flow depth). Each of the 11 experiments involved centerline measurements of three-dimensional velocity vectors, water surface profiles, and bed pressures and forces. The structure of flow over rib roughness consists of a pair of principal vortices of opposite sign set up by the ribs. These vortices are superimposed on an overall double- (time and space)-averaged velocity profile that is (quasi-) logarithmic above roughness tops, and that below roughness tops changes with increasing rib spacing from exponential (lambda/h < 10) to linear (lambda/h >= 10) to logarithmic (lambda/h >> 10). The measured double-averaged velocity profiles are parameterized herein, and double-averaged Reynolds and form-induced stress profiles and trends are also identified. Maximum drag due to wall roughness is found to occur for lambda/h approximate to 8. The experimentally determined momentum balance, including effects of secondary currents and flow acceleration, is found to agree well with theoretical expectations. It is shown that the knowledge of the effects of form-induced stresses, secondary currents, and flow nonuniformity may be particularly important for describing and modeling flows over roughness elements.

KW - turbulent flow

KW - boundary layers

KW - bed roughness

KW - velocity profile

KW - fluid dynamics

KW - spatial analysis

KW - boundary-layers

KW - channel flow

KW - rough-bed

KW - wall

KW - velocity

KW - resistance

KW - simulation

U2 - 10.1061/(ASCE)0733-9399(2007)133:2(194)

DO - 10.1061/(ASCE)0733-9399(2007)133:2(194)

M3 - Article

VL - 133

SP - 194

EP - 204

JO - Journal of Engineering Mechanics

JF - Journal of Engineering Mechanics

SN - 0733-9399

IS - 2

ER -