Nebkha Flow Dynamics and Shadow Dune Formation

Hesp, P.A. and Smyth, T.A.G. (2017) Nebkha Flow Dynamics and Shadow Dune Formation. Geomorphology, 282. pp. 27-38. ISSN 0169-555X (Accepted for Publication)

Hesp and Smyth 2017 (1).pdf - Accepted Version

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In this study, wind flow is simulated via CFD over five ‘nebkha’ dune forms that range in
shape from a cone, to a hemisphere (approximately) and to a dome in order to examine the
structure of the wake zone formed downwind and the effect on the leeward flow separation
zone and shadow dune formation. Dune height was fixed at 0.5 m while the nebkha diameter
increased in 0.25 m increments from 0.5 m to 1.5 m and aspect ratio (h/D) from 1.0 to 0.3.
The mean flow comprises an upwind region of reduced velocity which expands as nebkha
width increases, high velocity marginal wings, and paired counter-rotating reversing vortices
leeward of the nebkha. The point at which flow separation occurs moves further downwind as
the nebkha diameter increases. The core regions of the reversing vortices are situated further
downwind behind the smaller nebkha than in the case of the larger nebkha. These factors in
combination allow for higher velocity perturbations (TKE) and narrower wake behind the
smaller nebkha, and the suppression of downwind wake development in the case of the
increasingly larger nebkha. Shadow dune length increases as nebkha width increases for
lower incident velocity flow and is barely affected by nebkha width at higher flows. The
extent of the leeward separation or wake zone, and hence shadow dune length, more strongly
varies as a function of wind velocity.

Item Type: Article
Faculty / Department: Faculty of Science > Geography and Environmental Science
Depositing User: Thomas Smyth
Date Deposited: 12 Jan 2017 16:18
Last Modified: 13 Mar 2018 06:52

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