### Abstract

Turbulent flow of a rough-wall pipe is simulated using Direct Numerical Simulations (DNS) at low and medium Reynolds number from the transitionally rough regime to the fully rough regime. The rough surfaces simulated consist of three-dimensional sinusoidal roughness elements. The size of the roughness (roughness semi-amplitude height h^{+} and wavelength λ+) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. A method is developed to accurately calculate the roughness function ΔU^{+} for the simulations conducted at low Reynolds number. For this surface, the flow is fully rough when h^{+} ≈ 60 (simulated at Re_{τ} = 540). This corresponds to k^{+}_{s} ≈ 4.1h+ where k^{+}_{s} is Nikuradse's equivalent sandgrain roughness. A linear trend is observed when the ratio of the apparent wall shear stress due to form drag on the roughness elements to the total wall shear stress R_{τ} = τR/τT is plotted against the log of the roughness height h^{+}. This linear trend is also observed in the transitionally rough regime. For all the rough-wall pipe simulations conducted, Townsend's [15] outer layer similarity hypothesis holds true.

Original language | English |
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Title of host publication | Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014 |

Publisher | Australasian Fluid Mechanics Society |

ISBN (Electronic) | 9780646596952 |

Publication status | Published - 01 Jan 2014 |

Event | 19th Australasian Fluid Mechanics Conference, AFMC 2014 - Melbourne, Australia Duration: 08 Dec 2014 → 11 Dec 2014 |

### Publication series

Name | Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014 |
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### Other

Other | 19th Australasian Fluid Mechanics Conference, AFMC 2014 |
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Country | Australia |

City | Melbourne |

Period | 08/12/14 → 11/12/14 |

### Fingerprint

### All Science Journal Classification (ASJC) codes

- Fluid Flow and Transfer Processes

### Cite this

*Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014*(Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014). Australasian Fluid Mechanics Society.

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*Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014.*Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014, Australasian Fluid Mechanics Society, 19th Australasian Fluid Mechanics Conference, AFMC 2014, Melbourne, Australia, 08/12/14.

**Numerical simulation of a rough-wall pipe from the transitionally rough regime to the fully rough regime.** / Chan, Leon Zen Hsien; MacDonald, M.; Chung, D.; Hutchins, N.; Ooi, A.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

TY - GEN

T1 - Numerical simulation of a rough-wall pipe from the transitionally rough regime to the fully rough regime

AU - Chan, Leon Zen Hsien

AU - MacDonald, M.

AU - Chung, D.

AU - Hutchins, N.

AU - Ooi, A.

PY - 2014/1/1

Y1 - 2014/1/1

N2 - Turbulent flow of a rough-wall pipe is simulated using Direct Numerical Simulations (DNS) at low and medium Reynolds number from the transitionally rough regime to the fully rough regime. The rough surfaces simulated consist of three-dimensional sinusoidal roughness elements. The size of the roughness (roughness semi-amplitude height h+ and wavelength λ+) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. A method is developed to accurately calculate the roughness function ΔU+ for the simulations conducted at low Reynolds number. For this surface, the flow is fully rough when h+ ≈ 60 (simulated at Reτ = 540). This corresponds to k+s ≈ 4.1h+ where k+s is Nikuradse's equivalent sandgrain roughness. A linear trend is observed when the ratio of the apparent wall shear stress due to form drag on the roughness elements to the total wall shear stress Rτ = τR/τT is plotted against the log of the roughness height h+. This linear trend is also observed in the transitionally rough regime. For all the rough-wall pipe simulations conducted, Townsend's [15] outer layer similarity hypothesis holds true.

AB - Turbulent flow of a rough-wall pipe is simulated using Direct Numerical Simulations (DNS) at low and medium Reynolds number from the transitionally rough regime to the fully rough regime. The rough surfaces simulated consist of three-dimensional sinusoidal roughness elements. The size of the roughness (roughness semi-amplitude height h+ and wavelength λ+) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. A method is developed to accurately calculate the roughness function ΔU+ for the simulations conducted at low Reynolds number. For this surface, the flow is fully rough when h+ ≈ 60 (simulated at Reτ = 540). This corresponds to k+s ≈ 4.1h+ where k+s is Nikuradse's equivalent sandgrain roughness. A linear trend is observed when the ratio of the apparent wall shear stress due to form drag on the roughness elements to the total wall shear stress Rτ = τR/τT is plotted against the log of the roughness height h+. This linear trend is also observed in the transitionally rough regime. For all the rough-wall pipe simulations conducted, Townsend's [15] outer layer similarity hypothesis holds true.

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M3 - Conference contribution

T3 - Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014

BT - Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014

PB - Australasian Fluid Mechanics Society

ER -