CFD flow dynamics over model scarps and slopes

Knowledge of wind flow over dune scarps and, as scarps fill, their subsequent various slopes, is important for understanding sediment transport pathways from beach to dunes. In this study, flow over scarps (also termed forward-facing steps) is reviewed, and the flow over a vertical scarp (90°) and three slopes of 45°, 24°, and 14°, all 2min height, is examined via CFD modelling. The flow over three 90° scarps, with heights of 1 m, 2mand 4m, and over a 2-mhigh vertical (90°) scarp for three oblique incident winds is studied. The extent of wind flow deceleration and separation becomes smaller with decreased slope, with maximum flow separation and reverse vortex development occurring on the vertical scarp. The extent of crest wind flow separation is greatest for the scarp and considerably less for the 45° slope. As scarp height increases, so too does the spatial extent of turbulent wind flow, wind speed, and extent of the flow separation region. As incident wind direction became more oblique over a vertical scarp, less deceleration occurs, and helicoidal vortices replace roller vortices. Our results demonstrate how scarp morphology and wind direction are likely to influence transport pathways.