The influence of foredune geometry on wind flow quantified from computational fluid dynamics simulations

Abstract

Wind flow over a coastal foredune is driven by a complex interplay of dune geometry, sand transport, and vegetation dynamics. While previous studies have explored the influence of foredune geometry and wind direction on wind flow, their combined effects remain underexplored. This study employs 3D computational fluid dynamics to investigate the impact of foredune height, stoss slope, and incident wind direction on wind flow along the seaward side. Model accuracy was validated against field measurements, then used to simulate wind flow over an idealized foredune with varying heights and slopes across 11 wind directions. Results show that foredune height has the strongest influence on flow speed-up and directional deviations. The highest (25 m) and steepest (1:2) dune experiences the largest speed-up (12) under shore-normal winds, decreasing to 4 for a 1:4 slope and to 1 for alongshore winds. For a 6 m high foredune, speed-up remains around 2, dropping to 1 only for highly oblique winds. Angle deviations across the foredune peak at 30 to 60° wind incidence, and can be up to 20° at the dune toe and crest for the highest and steepest foredune in the simulations. This study demonstrates how combined dune geometry properties – specifically height and slope – along with the incident wind direction influence wind speed-up over foredunes. These findings improve our understanding of sand transport, coastal dune evolution, and artificial dune design, particularly in anticipation of future work that will couple wind flow models with sediment transport models to assess morphological changes under varying wind conditions.