A Multi-Mechanism Model for the Velocity Profile in Vegetated Open-Channel Flows

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

Abstract

Velocity profiles in vegetated channels reflect multiple mechanisms of flow-vegetation interactions and determine bulk flow velocity, and hence the overall hydraulic resistance. Most existing velocity profile models are based on single physical concepts that are used for theoretical considerations and data interpretation. However, measured velocity profiles in vegetated flows show that the use of a single concept is not only insufficient to explain all transport and turbulence production mechanisms, but also does not cover all flow-vegetation scenarios. To address these issues a number of researchers have expressed velocity profiles as a set of linked segments with different approximations, i.e., within each non-overlapping segment a different physical concept is applied. While such segmented models have improved our understanding of flow-vegetation interactions, new conceptual approaches and analytical formulations describing the flow structure are still required. In this paper we propose a new approach where a vertical velocity profile in vegetated channels is modeled as a linear superposition of four concepts applied over the whole flow depth: (1) uniform velocity distribution; (2) mixing layer analogy concept and associated hyperbolic tangent profile; (3) boundary layer concept and its logarithmic profile; and (4) the wake function concept. Using this approach, a new analytical model is developed. The proposed analytical expression combines these concepts simultaneously over the whole flow depth allowing significant overlaps of momentum transport and turbulence production mechanisms. The model is successfully tested using extensive laboratory experiments covering wide ranges of background flow and vegetation parameters.
Original languageEnglish
Title of host publicationProceedings of the 35rd Congress of IAHR, Chengdu, China
PublisherIAHR
Pages153-162
Number of pages10
ISBN (Print)978-1-62993-814-1
Publication statusPublished - 2013
Event35th IAHR Congress - Chengdu, China
Duration: 8 Aug 2013 → …

Conference

Conference35th IAHR Congress
CountryChina
CityChengdu
Period8/08/13 → …

Fingerprint

open channel flow
velocity profile
vegetation
turbulence
data interpretation
flow structure
flow velocity
momentum
boundary layer
hydraulics

Keywords

  • Vertical Velocity Profile
  • Boundary Layer
  • Log Law
  • Mixing Layer
  • Wake Function

Cite this

Nikora, N., Nikora, V. I., & O'Donoghue, T. (2013). A Multi-Mechanism Model for the Velocity Profile in Vegetated Open-Channel Flows. In Proceedings of the 35rd Congress of IAHR, Chengdu, China (pp. 153-162). IAHR.

A Multi-Mechanism Model for the Velocity Profile in Vegetated Open-Channel Flows. / Nikora, Nina; Nikora, Vladimir I.; O'Donoghue, Tom.

Proceedings of the 35rd Congress of IAHR, Chengdu, China. IAHR, 2013. p. 153-162.

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

Nikora, N, Nikora, VI & O'Donoghue, T 2013, A Multi-Mechanism Model for the Velocity Profile in Vegetated Open-Channel Flows. in Proceedings of the 35rd Congress of IAHR, Chengdu, China. IAHR, pp. 153-162, 35th IAHR Congress, Chengdu, China, 8/08/13.
Nikora N, Nikora VI, O'Donoghue T. A Multi-Mechanism Model for the Velocity Profile in Vegetated Open-Channel Flows. In Proceedings of the 35rd Congress of IAHR, Chengdu, China. IAHR. 2013. p. 153-162
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N2 - Velocity profiles in vegetated channels reflect multiple mechanisms of flow-vegetation interactions and determine bulk flow velocity, and hence the overall hydraulic resistance. Most existing velocity profile models are based on single physical concepts that are used for theoretical considerations and data interpretation. However, measured velocity profiles in vegetated flows show that the use of a single concept is not only insufficient to explain all transport and turbulence production mechanisms, but also does not cover all flow-vegetation scenarios. To address these issues a number of researchers have expressed velocity profiles as a set of linked segments with different approximations, i.e., within each non-overlapping segment a different physical concept is applied. While such segmented models have improved our understanding of flow-vegetation interactions, new conceptual approaches and analytical formulations describing the flow structure are still required. In this paper we propose a new approach where a vertical velocity profile in vegetated channels is modeled as a linear superposition of four concepts applied over the whole flow depth: (1) uniform velocity distribution; (2) mixing layer analogy concept and associated hyperbolic tangent profile; (3) boundary layer concept and its logarithmic profile; and (4) the wake function concept. Using this approach, a new analytical model is developed. The proposed analytical expression combines these concepts simultaneously over the whole flow depth allowing significant overlaps of momentum transport and turbulence production mechanisms. The model is successfully tested using extensive laboratory experiments covering wide ranges of background flow and vegetation parameters.

AB - Velocity profiles in vegetated channels reflect multiple mechanisms of flow-vegetation interactions and determine bulk flow velocity, and hence the overall hydraulic resistance. Most existing velocity profile models are based on single physical concepts that are used for theoretical considerations and data interpretation. However, measured velocity profiles in vegetated flows show that the use of a single concept is not only insufficient to explain all transport and turbulence production mechanisms, but also does not cover all flow-vegetation scenarios. To address these issues a number of researchers have expressed velocity profiles as a set of linked segments with different approximations, i.e., within each non-overlapping segment a different physical concept is applied. While such segmented models have improved our understanding of flow-vegetation interactions, new conceptual approaches and analytical formulations describing the flow structure are still required. In this paper we propose a new approach where a vertical velocity profile in vegetated channels is modeled as a linear superposition of four concepts applied over the whole flow depth: (1) uniform velocity distribution; (2) mixing layer analogy concept and associated hyperbolic tangent profile; (3) boundary layer concept and its logarithmic profile; and (4) the wake function concept. Using this approach, a new analytical model is developed. The proposed analytical expression combines these concepts simultaneously over the whole flow depth allowing significant overlaps of momentum transport and turbulence production mechanisms. The model is successfully tested using extensive laboratory experiments covering wide ranges of background flow and vegetation parameters.

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