Computational fluid dynamics and the physical modelling of an upland urban river

Ma Lin, Philip Ashworth, James L. Best, Lionel Elliott, Derek B. Ingham, Leslie J. Whitcombe

Research output: Contribution to journalArticleResearchpeer-review

Abstract

This paper describes the application of a commercially available, three-dimensional computational fluid dynamic (CFD) model to simulate the flow structure in an upland river that is prone to flooding. Simulations use a rectangular channel geometry, smooth sidewalls and a bed topography obtained from the field site that contains a subdued pool–riffle sequence. The CFD model uses the RNG κ–var epsilon turbulence closure scheme of Yakhot and Orszag (J. Sci. Comput. 1 (1986) 1), as implemented in FLUENT 4.4.4, with a free surface. Results are shown for numerical runs simulating a 1:100 year return interval flood. Output from the numerical model is compared to a physical model experiment that uses a 1:35 scale fibreglass mould of the field study reach and measures velocity using ultrasonic Doppler velocity profiling (UDVP). Results are presented from the numerical and flume models for the water surface and streamwise velocity pattern and for the secondary flows simulated in the numerical model. A good agreement is achieved between the CFD model output and the physical model results for the downstream velocities. Results suggest that the streamwise velocity is the main influence on the flow structure at the discharge and channel configuration studied. Secondary flows are, in general, very weak being below the resolution of measurement in the physical model and less than 10% of the streamwise velocity in the numerical model. Consequently, there is no evidence for a ‘velocity dip’. It is suggested that the subdued topography or inlet morphology may inhibit the development of secondary flows that have been recorded in previous flat-bed, rectangular open channel flows. A significant corollary of these results is that the morphological evolution of the pool–riffle sequence at high discharges may be controlled primarily by the downstream distribution of velocity and sediment transport with little role for lateral sorting and sediment routing by secondary flows. This paper also raises a number of issues that may be of use in future CFD modelling of three-dimensional flow in open channels within the geomorphological community.
Original languageEnglish
Pages (from-to)375-391
Number of pages17
JournalGeomorphology
Volume44
Issue number3-4
Publication statusPublished - May 2002

Fingerprint

computational fluid dynamics
secondary flow
river
modeling
flow structure
topography
open channel flow
three-dimensional flow
routing
sorting
sediment transport
dip
flooding
turbulence
surface water
geometry
sediment
simulation

Keywords

  • Computational fluid dynamics
  • Pool–riffle
  • Secondary flows
  • Upland river
  • Physical model

Cite this

Lin, M., Ashworth, P., Best, J. L., Elliott, L., Ingham, D. B., & Whitcombe, L. J. (2002). Computational fluid dynamics and the physical modelling of an upland urban river. Geomorphology, 44(3-4), 375-391.
Lin, Ma ; Ashworth, Philip ; Best, James L. ; Elliott, Lionel ; Ingham, Derek B. ; Whitcombe, Leslie J. / Computational fluid dynamics and the physical modelling of an upland urban river. In: Geomorphology. 2002 ; Vol. 44, No. 3-4. pp. 375-391.
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abstract = "This paper describes the application of a commercially available, three-dimensional computational fluid dynamic (CFD) model to simulate the flow structure in an upland river that is prone to flooding. Simulations use a rectangular channel geometry, smooth sidewalls and a bed topography obtained from the field site that contains a subdued pool–riffle sequence. The CFD model uses the RNG κ–var epsilon turbulence closure scheme of Yakhot and Orszag (J. Sci. Comput. 1 (1986) 1), as implemented in FLUENT 4.4.4, with a free surface. Results are shown for numerical runs simulating a 1:100 year return interval flood. Output from the numerical model is compared to a physical model experiment that uses a 1:35 scale fibreglass mould of the field study reach and measures velocity using ultrasonic Doppler velocity profiling (UDVP). Results are presented from the numerical and flume models for the water surface and streamwise velocity pattern and for the secondary flows simulated in the numerical model. A good agreement is achieved between the CFD model output and the physical model results for the downstream velocities. Results suggest that the streamwise velocity is the main influence on the flow structure at the discharge and channel configuration studied. Secondary flows are, in general, very weak being below the resolution of measurement in the physical model and less than 10{\%} of the streamwise velocity in the numerical model. Consequently, there is no evidence for a ‘velocity dip’. It is suggested that the subdued topography or inlet morphology may inhibit the development of secondary flows that have been recorded in previous flat-bed, rectangular open channel flows. A significant corollary of these results is that the morphological evolution of the pool–riffle sequence at high discharges may be controlled primarily by the downstream distribution of velocity and sediment transport with little role for lateral sorting and sediment routing by secondary flows. This paper also raises a number of issues that may be of use in future CFD modelling of three-dimensional flow in open channels within the geomorphological community.",
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Lin, M, Ashworth, P, Best, JL, Elliott, L, Ingham, DB & Whitcombe, LJ 2002, 'Computational fluid dynamics and the physical modelling of an upland urban river', Geomorphology, vol. 44, no. 3-4, pp. 375-391.

Computational fluid dynamics and the physical modelling of an upland urban river. / Lin, Ma; Ashworth, Philip; Best, James L.; Elliott, Lionel; Ingham, Derek B.; Whitcombe, Leslie J.

In: Geomorphology, Vol. 44, No. 3-4, 05.2002, p. 375-391.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Computational fluid dynamics and the physical modelling of an upland urban river

AU - Lin, Ma

AU - Ashworth, Philip

AU - Best, James L.

AU - Elliott, Lionel

AU - Ingham, Derek B.

AU - Whitcombe, Leslie J.

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N2 - This paper describes the application of a commercially available, three-dimensional computational fluid dynamic (CFD) model to simulate the flow structure in an upland river that is prone to flooding. Simulations use a rectangular channel geometry, smooth sidewalls and a bed topography obtained from the field site that contains a subdued pool–riffle sequence. The CFD model uses the RNG κ–var epsilon turbulence closure scheme of Yakhot and Orszag (J. Sci. Comput. 1 (1986) 1), as implemented in FLUENT 4.4.4, with a free surface. Results are shown for numerical runs simulating a 1:100 year return interval flood. Output from the numerical model is compared to a physical model experiment that uses a 1:35 scale fibreglass mould of the field study reach and measures velocity using ultrasonic Doppler velocity profiling (UDVP). Results are presented from the numerical and flume models for the water surface and streamwise velocity pattern and for the secondary flows simulated in the numerical model. A good agreement is achieved between the CFD model output and the physical model results for the downstream velocities. Results suggest that the streamwise velocity is the main influence on the flow structure at the discharge and channel configuration studied. Secondary flows are, in general, very weak being below the resolution of measurement in the physical model and less than 10% of the streamwise velocity in the numerical model. Consequently, there is no evidence for a ‘velocity dip’. It is suggested that the subdued topography or inlet morphology may inhibit the development of secondary flows that have been recorded in previous flat-bed, rectangular open channel flows. A significant corollary of these results is that the morphological evolution of the pool–riffle sequence at high discharges may be controlled primarily by the downstream distribution of velocity and sediment transport with little role for lateral sorting and sediment routing by secondary flows. This paper also raises a number of issues that may be of use in future CFD modelling of three-dimensional flow in open channels within the geomorphological community.

AB - This paper describes the application of a commercially available, three-dimensional computational fluid dynamic (CFD) model to simulate the flow structure in an upland river that is prone to flooding. Simulations use a rectangular channel geometry, smooth sidewalls and a bed topography obtained from the field site that contains a subdued pool–riffle sequence. The CFD model uses the RNG κ–var epsilon turbulence closure scheme of Yakhot and Orszag (J. Sci. Comput. 1 (1986) 1), as implemented in FLUENT 4.4.4, with a free surface. Results are shown for numerical runs simulating a 1:100 year return interval flood. Output from the numerical model is compared to a physical model experiment that uses a 1:35 scale fibreglass mould of the field study reach and measures velocity using ultrasonic Doppler velocity profiling (UDVP). Results are presented from the numerical and flume models for the water surface and streamwise velocity pattern and for the secondary flows simulated in the numerical model. A good agreement is achieved between the CFD model output and the physical model results for the downstream velocities. Results suggest that the streamwise velocity is the main influence on the flow structure at the discharge and channel configuration studied. Secondary flows are, in general, very weak being below the resolution of measurement in the physical model and less than 10% of the streamwise velocity in the numerical model. Consequently, there is no evidence for a ‘velocity dip’. It is suggested that the subdued topography or inlet morphology may inhibit the development of secondary flows that have been recorded in previous flat-bed, rectangular open channel flows. A significant corollary of these results is that the morphological evolution of the pool–riffle sequence at high discharges may be controlled primarily by the downstream distribution of velocity and sediment transport with little role for lateral sorting and sediment routing by secondary flows. This paper also raises a number of issues that may be of use in future CFD modelling of three-dimensional flow in open channels within the geomorphological community.

KW - Computational fluid dynamics

KW - Pool–riffle

KW - Secondary flows

KW - Upland river

KW - Physical model

M3 - Article

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SP - 375

EP - 391

JO - Geomorphology

JF - Geomorphology

SN - 0169-555x

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Lin M, Ashworth P, Best JL, Elliott L, Ingham DB, Whitcombe LJ. Computational fluid dynamics and the physical modelling of an upland urban river. Geomorphology. 2002 May;44(3-4):375-391.