Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime

Leon Zen Hsien Chan, M. MaCdonald, N. Hutchins, D. Chung, A. Ooi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Direct Numerical Simulations (DNS) are earned out in a turbulent rough-wall pipe at low and medium Reynolds numbers. The rough surface, which is comprised of three-dimensional sinusoidal roughness elements, was viscously scaled from the transitionally rough regime to the fully rough regime. The main aim of this study is to analyse the behaviour of the near-wall cycle as the surface condition changes from smooth through to fully rough. When analysing the streamwise velocity, a triple decomposition is used to distinguish between the fluctuations due to the spatial variation with the actual turbulent fluctuations. For small roughness height (h+ < 15), the near-wall cycle streaks occurs above the roughness elements. Although the high and low speed streaks look similar to the smooth wall when visually inspected, subtle differences are observed when the premultiplied energy spectra are analysed. When the flow is fully rough, the near-wall cycle is replaced by the stationary features of the flow which dominate within the roughness elements. We also analyse the contribution of the apparent wall shear stress due to form (pressure) drag (τR) expressed as a ratio between form and total shear stress (Rτ = τRT. In the fully rough regime, the form drag dominates (Rτ > 0.75) and disrupts the near-wall cycle. Townsend's outer layer similarity is observed when the wall normal height normalised by the mean radius of the pipe y/R0 is greater than 0.56, where a collapse in the streamwise premultiplied energy spectra is obtained.

Original languageEnglish
Title of host publication9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015
PublisherTSFP-9
ISBN (Electronic)9780000000002
Publication statusPublished - 01 Jan 2015
Event9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015 - Melbourne, Australia
Duration: 30 Jun 201503 Jul 2015

Publication series

Name9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015
Volume1

Other

Other9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015
CountryAustralia
CityMelbourne
Period30/06/1503/07/15

Fingerprint

Turbulent flow
Surface roughness
Pipe
Direct numerical simulation
Reynolds number
Decomposition

All Science Journal Classification (ASJC) codes

  • Fluid Flow and Transfer Processes

Cite this

Chan, L. Z. H., MaCdonald, M., Hutchins, N., Chung, D., & Ooi, A. (2015). Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime. In 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015 (9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015; Vol. 1). TSFP-9.
Chan, Leon Zen Hsien ; MaCdonald, M. ; Hutchins, N. ; Chung, D. ; Ooi, A. / Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime. 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. TSFP-9, 2015. (9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015).
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abstract = "Direct Numerical Simulations (DNS) are earned out in a turbulent rough-wall pipe at low and medium Reynolds numbers. The rough surface, which is comprised of three-dimensional sinusoidal roughness elements, was viscously scaled from the transitionally rough regime to the fully rough regime. The main aim of this study is to analyse the behaviour of the near-wall cycle as the surface condition changes from smooth through to fully rough. When analysing the streamwise velocity, a triple decomposition is used to distinguish between the fluctuations due to the spatial variation with the actual turbulent fluctuations. For small roughness height (h+ < 15), the near-wall cycle streaks occurs above the roughness elements. Although the high and low speed streaks look similar to the smooth wall when visually inspected, subtle differences are observed when the premultiplied energy spectra are analysed. When the flow is fully rough, the near-wall cycle is replaced by the stationary features of the flow which dominate within the roughness elements. We also analyse the contribution of the apparent wall shear stress due to form (pressure) drag (τR) expressed as a ratio between form and total shear stress (Rτ = τR/τT. In the fully rough regime, the form drag dominates (Rτ > 0.75) and disrupts the near-wall cycle. Townsend's outer layer similarity is observed when the wall normal height normalised by the mean radius of the pipe y/R0 is greater than 0.56, where a collapse in the streamwise premultiplied energy spectra is obtained.",
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Chan, LZH, MaCdonald, M, Hutchins, N, Chung, D & Ooi, A 2015, Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime. in 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015, vol. 1, TSFP-9, 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015, Melbourne, Australia, 30/06/15.

Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime. / Chan, Leon Zen Hsien; MaCdonald, M.; Hutchins, N.; Chung, D.; Ooi, A.

9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. TSFP-9, 2015. (9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015; Vol. 1).

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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AB - Direct Numerical Simulations (DNS) are earned out in a turbulent rough-wall pipe at low and medium Reynolds numbers. The rough surface, which is comprised of three-dimensional sinusoidal roughness elements, was viscously scaled from the transitionally rough regime to the fully rough regime. The main aim of this study is to analyse the behaviour of the near-wall cycle as the surface condition changes from smooth through to fully rough. When analysing the streamwise velocity, a triple decomposition is used to distinguish between the fluctuations due to the spatial variation with the actual turbulent fluctuations. For small roughness height (h+ < 15), the near-wall cycle streaks occurs above the roughness elements. Although the high and low speed streaks look similar to the smooth wall when visually inspected, subtle differences are observed when the premultiplied energy spectra are analysed. When the flow is fully rough, the near-wall cycle is replaced by the stationary features of the flow which dominate within the roughness elements. We also analyse the contribution of the apparent wall shear stress due to form (pressure) drag (τR) expressed as a ratio between form and total shear stress (Rτ = τR/τT. In the fully rough regime, the form drag dominates (Rτ > 0.75) and disrupts the near-wall cycle. Townsend's outer layer similarity is observed when the wall normal height normalised by the mean radius of the pipe y/R0 is greater than 0.56, where a collapse in the streamwise premultiplied energy spectra is obtained.

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M3 - Conference contribution

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PB - TSFP-9

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Chan LZH, MaCdonald M, Hutchins N, Chung D, Ooi A. Investigation of a turbulent flow from the transitionally rough regime to the fully rough regime. In 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. TSFP-9. 2015. (9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015).