Bed slope effects on turbulent wave boundary layers: 1. Model validation and quantification of rough-turbulent results

Publication: Research - peer-reviewJournal article – Annual report year: 2009

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@article{056501bff1c24c19ad23195056788404,
title = "Bed slope effects on turbulent wave boundary layers: 1. Model validation and quantification of rough-turbulent results",
publisher = "American Geophysical Union",
author = "Fuhrman, {David R.} and Jørgen Fredsøe and Sumer, {B. Mutlu}",
year = "2009",
doi = "10.1029/2008JC005045",
volume = "114",
number = "3",
journal = "Journal of Geophysical Research - Oceans",
issn = "0148-0227",

}

RIS

TY - JOUR

T1 - Bed slope effects on turbulent wave boundary layers: 1. Model validation and quantification of rough-turbulent results

A1 - Fuhrman,David R.

A1 - Fredsøe,Jørgen

A1 - Sumer,B. Mutlu

AU - Fuhrman,David R.

AU - Fredsøe,Jørgen

AU - Sumer,B. Mutlu

PB - American Geophysical Union

PY - 2009

Y1 - 2009

N2 - A numerical model solving incompressible Reynolds-averaged Navier-Stokes equations, combined with a two-equation k-omega turbulence closure, is used to study converging-diverging effects from a sloping bed on turbulent (oscillatory) wave boundary layers. Bed shear stresses from the numerical model are first validated against hydraulically smooth and rough data from flat bed experiments in the form of wave friction factor diagrams. The results show that the model provides acceptable accuracy for wave orbital amplitude to roughness length ratios a/k(N) >= 20. Validation against experimental measurements for steady streaming induced by a skewed free stream velocity signal is also provided. We then simulate a series of experiments involving oscillatory flow in a convergent-divergent smooth tunnel, and a good match with respect to bed shear stresses and streaming velocities is achieved. The streaming is conceptually explained using analogies from steady converging and diffuser flows. A parametric study is undertaken to assess both the peak and time-averaged bed shear stresses in converging and diverging half periods under rough-turbulent conditions. The results are presented as friction factor diagrams. A local similarity condition is derived for relating oscillatory flow in a convergent-divergent tunnel, as considered herein, to shoaling shallow-water waves by matching spatial gradients in the free stream orbital length.

AB - A numerical model solving incompressible Reynolds-averaged Navier-Stokes equations, combined with a two-equation k-omega turbulence closure, is used to study converging-diverging effects from a sloping bed on turbulent (oscillatory) wave boundary layers. Bed shear stresses from the numerical model are first validated against hydraulically smooth and rough data from flat bed experiments in the form of wave friction factor diagrams. The results show that the model provides acceptable accuracy for wave orbital amplitude to roughness length ratios a/k(N) >= 20. Validation against experimental measurements for steady streaming induced by a skewed free stream velocity signal is also provided. We then simulate a series of experiments involving oscillatory flow in a convergent-divergent smooth tunnel, and a good match with respect to bed shear stresses and streaming velocities is achieved. The streaming is conceptually explained using analogies from steady converging and diffuser flows. A parametric study is undertaken to assess both the peak and time-averaged bed shear stresses in converging and diverging half periods under rough-turbulent conditions. The results are presented as friction factor diagrams. A local similarity condition is derived for relating oscillatory flow in a convergent-divergent tunnel, as considered herein, to shoaling shallow-water waves by matching spatial gradients in the free stream orbital length.

U2 - 10.1029/2008JC005045

DO - 10.1029/2008JC005045

JO - Journal of Geophysical Research - Oceans

JF - Journal of Geophysical Research - Oceans

SN - 0148-0227

IS - 3

VL - 114

ER -