Physical and numerical modelling of negative surges in open channels

Reichstetter, Martina and Chanson, Hubert (2011) Physical and numerical modelling of negative surges in open channels Brisbane, Australia:

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Author Reichstetter, Martina
Chanson, Hubert
Title of report Physical and numerical modelling of negative surges in open channels
Parent publication School of Civil Engineering, The University of Queensland
Publication date 2011-10
ISBN 9781742720388
Open Access Status File (Publisher version)
Series Hydraulic Model Report No. CH84/11
Place of publication Brisbane, Australia
Start page 1
End page 82
Total pages 82
Language eng
Subjects 0905 Civil Engineering
090509 Water Resources Engineering
Abstract/Summary Negative surges are caused by a sudden change in flow resulting from a decrease in water depth. New experiments were conducted in a horizontal channel (L = 12 m, W = 0.5 m) to record the unsteady water depth and turbulence in negative surges propagating upstream against an initiallysteady flow. The data were collected using video-imagery, acoustic displacement meters and acoustic Doppler velocimetry (ADV). The physical observations showed that the leading edge of negative surge propagated upstream with a celerity which varied with time. During the first initial instants following the surge formation, the negative surge leading edge accelerated ad its celerity increased with time up to xGate-x = 4do. After the acceleration phase, the negative surge propagation was more gradual: the surge leading edge was very flat and barely perceptible, and its celerity tended to decrease slowly with increasing distance from the gate. The data implied some deceleration in a manner which is contrary to theoretical considerations. The physical measurements highlighted that the negative surges were associated with some flow acceleration. The turbulent velocity data highlighted some increased turbulence occurring beneath the negative surge with large velocity fluctuations and large Reynolds stress components. The velocity fluctuations and turbulent stresses were significantly larger than in the initially steady flow and in the final flow motion. The physical data were used to test an analytical solution of the Saint-Venant equations (the simple wave solution) and some 1-D and 2-D numerical model results. The findings showed that the negative surge propagation was relatively little affected by the boundary friction. For a relatively simple geometry such as the prismatic rectangular flume used in the present study, the physical data were best modelled by the simple wave theory, although the numerical model results were qualitatively in agreement with the experimental observations. The present results suggested that the negative surge remains a challenging topic for the computational modellers.
Keyword Negative surges
Unsteady open channel flow
Physical modelling
Numerical modelling
Turbulent Reynolds stress tensor
Negative waves
Q-Index Code AX
Q-Index Status Provisional Code
Institutional Status UQ
Additional Notes The full bibliographic details are: REICHSTETTER, M., and CHANSON, H. (2011). "Physical and Numerical Modelling of Negative Surges in Open Channels." Hydraulic Model Report No. CH84/11, School of Civil Engineering, The University of Queensland, Brisbane, Australia, 82 pages (ISBN 9781742720388).

Document type: Research Report
Collection: School of Civil Engineering Publications
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Created: Fri, 23 Dec 2011, 09:00:51 EST by Hubert Chanson on behalf of School of Civil Engineering