Power-law index for velocity profiles in open channel flows

Turbulence theory has demonstrated that the log law is one of the established theoretical results for describing velocity profiles, which is in principle applicable for the near-bed overlap region, being less than about 20% of the flow depth. In comparison, the power law that is often presented in a...

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Main Author: Cheng, Nian-Sheng
Other Authors: School of Civil and Environmental Engineering
Format: Article
Language:English
Published: 2012
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Online Access:https://hdl.handle.net/10356/83702
http://hdl.handle.net/10220/7645
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-837022020-03-07T11:43:37Z Power-law index for velocity profiles in open channel flows Cheng, Nian-Sheng School of Civil and Environmental Engineering DRNTU::Engineering::Civil engineering::Water resources Turbulence theory has demonstrated that the log law is one of the established theoretical results for describing velocity profiles, which is in principle applicable for the near-bed overlap region, being less than about 20% of the flow depth. In comparison, the power law that is often presented in an empirical fashion could apply to larger fraction of the flow domain. However, limited information is available for evaluating the power-law exponent or index. This paper attempts to show that the power law can be derived as a first-order approximation to the log law, and its power-law index is computed as a function of the Reynolds number as well as the relative roughness height. The result obtained also coincides with the fact that the one-sixth power included in the Manning equation is of prevalent acceptance, while higher indexes would be required for flows over very rough boundaries. Accepted version 2012-03-21T08:28:13Z 2019-12-06T15:28:23Z 2012-03-21T08:28:13Z 2019-12-06T15:28:23Z 2007 2007 Journal Article Cheng, N. S. (2007). Power-law index for velocity profiles in open channel flows. Advances in Water Resources, 30(8), 1775-1784. https://hdl.handle.net/10356/83702 http://hdl.handle.net/10220/7645 10.1016/j.advwatres.2007.02.001 en Advances in water resources © 2007 Elsevier. This is the author created version of a work that has been peer reviewed and accepted for publication by Advances in Water Resources, Elsevier. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [DOI: http://dx.doi.org/10.1016/j.advwatres.2007.02.001] 34 p. application/pdf
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic DRNTU::Engineering::Civil engineering::Water resources
spellingShingle DRNTU::Engineering::Civil engineering::Water resources
Cheng, Nian-Sheng
Power-law index for velocity profiles in open channel flows
description Turbulence theory has demonstrated that the log law is one of the established theoretical results for describing velocity profiles, which is in principle applicable for the near-bed overlap region, being less than about 20% of the flow depth. In comparison, the power law that is often presented in an empirical fashion could apply to larger fraction of the flow domain. However, limited information is available for evaluating the power-law exponent or index. This paper attempts to show that the power law can be derived as a first-order approximation to the log law, and its power-law index is computed as a function of the Reynolds number as well as the relative roughness height. The result obtained also coincides with the fact that the one-sixth power included in the Manning equation is of prevalent acceptance, while higher indexes would be required for flows over very rough boundaries.
author2 School of Civil and Environmental Engineering
author_facet School of Civil and Environmental Engineering
Cheng, Nian-Sheng
format Article
author Cheng, Nian-Sheng
author_sort Cheng, Nian-Sheng
title Power-law index for velocity profiles in open channel flows
title_short Power-law index for velocity profiles in open channel flows
title_full Power-law index for velocity profiles in open channel flows
title_fullStr Power-law index for velocity profiles in open channel flows
title_full_unstemmed Power-law index for velocity profiles in open channel flows
title_sort power-law index for velocity profiles in open channel flows
publishDate 2012
url https://hdl.handle.net/10356/83702
http://hdl.handle.net/10220/7645
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