Flow deflection over a foredune

Patrick Hesp, Thomas Smyth, Peter Nielsen, Ian Walker, Bernard Bauer, Robin Davidson-Arnott

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Flow deflection of surface winds is common across coastal foredunes and blowouts. Incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest-normal orientation across the stoss slope of the foredune. This paper examines field measurements for obliquely incident winds, and compares them to computational fluid dynamics (CFD) modelling of flow deflection in 10° increments from onshore (0°) to alongshore (90°) wind approach angles. The mechanics of flow deflection are discussed, followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement. CFD modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0° and gradually increases as the incident wind turns towards 30° to the dune crest. The greatest deflection occurs between 30° and 70° incident to the dune crest. The degree of flow deflection depends secondarily on height above the dune surface, with the greatest effect near the surface and toward the dune crest. Topographically forced flow acceleration (“speed-up”) across the stoss slope of the foredune is greatest for winds less than 30° (i.e., roughly perpendicular) and declines significantly for winds with more oblique approach angles. There is less lateral uniformity in the wind field when the incident wind approaches from N60° because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced.
LanguageEnglish
Pages67-74
Number of pages11
JournalGeomorphology
Volume230
Early online date20 Nov 2014
DOIs
Publication statusPublished - 1 Feb 2015
Externally publishedYes

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deflection
dune
computational fluid dynamics
wind field
surface wind
mechanics
modeling

Cite this

Hesp, P., Smyth, T., Nielsen, P., Walker, I., Bauer, B., & Davidson-Arnott, R. (2015). Flow deflection over a foredune. Geomorphology, 230, 67-74. https://doi.org/10.1016/j.geomorph.2014.11.005
Hesp, Patrick ; Smyth, Thomas ; Nielsen, Peter ; Walker, Ian ; Bauer, Bernard ; Davidson-Arnott, Robin. / Flow deflection over a foredune. In: Geomorphology. 2015 ; Vol. 230. pp. 67-74.
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Hesp, P, Smyth, T, Nielsen, P, Walker, I, Bauer, B & Davidson-Arnott, R 2015, 'Flow deflection over a foredune', Geomorphology, vol. 230, pp. 67-74. https://doi.org/10.1016/j.geomorph.2014.11.005

Flow deflection over a foredune. / Hesp, Patrick; Smyth, Thomas; Nielsen, Peter ; Walker, Ian; Bauer, Bernard; Davidson-Arnott, Robin.

In: Geomorphology, Vol. 230, 01.02.2015, p. 67-74.

Research output: Contribution to journalArticle

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N2 - Flow deflection of surface winds is common across coastal foredunes and blowouts. Incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest-normal orientation across the stoss slope of the foredune. This paper examines field measurements for obliquely incident winds, and compares them to computational fluid dynamics (CFD) modelling of flow deflection in 10° increments from onshore (0°) to alongshore (90°) wind approach angles. The mechanics of flow deflection are discussed, followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement. CFD modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0° and gradually increases as the incident wind turns towards 30° to the dune crest. The greatest deflection occurs between 30° and 70° incident to the dune crest. The degree of flow deflection depends secondarily on height above the dune surface, with the greatest effect near the surface and toward the dune crest. Topographically forced flow acceleration (“speed-up”) across the stoss slope of the foredune is greatest for winds less than 30° (i.e., roughly perpendicular) and declines significantly for winds with more oblique approach angles. There is less lateral uniformity in the wind field when the incident wind approaches from N60° because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced.

AB - Flow deflection of surface winds is common across coastal foredunes and blowouts. Incident winds approaching obliquely to the dune toe and crestline tend to be deflected towards a more crest-normal orientation across the stoss slope of the foredune. This paper examines field measurements for obliquely incident winds, and compares them to computational fluid dynamics (CFD) modelling of flow deflection in 10° increments from onshore (0°) to alongshore (90°) wind approach angles. The mechanics of flow deflection are discussed, followed by a comparative analysis of measured and modelled flow deflection data that shows strong agreement. CFD modelling of the full range of onshore to alongshore incident winds reveals that deflection of the incident wind flow is minimal at 0° and gradually increases as the incident wind turns towards 30° to the dune crest. The greatest deflection occurs between 30° and 70° incident to the dune crest. The degree of flow deflection depends secondarily on height above the dune surface, with the greatest effect near the surface and toward the dune crest. Topographically forced flow acceleration (“speed-up”) across the stoss slope of the foredune is greatest for winds less than 30° (i.e., roughly perpendicular) and declines significantly for winds with more oblique approach angles. There is less lateral uniformity in the wind field when the incident wind approaches from N60° because the effect of aspect ratio on topographic forcing and streamline convergence is less pronounced.

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Hesp P, Smyth T, Nielsen P, Walker I, Bauer B, Davidson-Arnott R. Flow deflection over a foredune. Geomorphology. 2015 Feb 1;230:67-74. https://doi.org/10.1016/j.geomorph.2014.11.005