Three-dimensional Computational Fluid Dynamic experiments over a complex dune topography

For modeling coastal dune systems the topography is often complex with complicating factors such as dune vegetation, sediment transport and the sand properties. Strategies such as simplifying the geometry and vegetation and no sediment transportation have been applied and provided insight into mechanisms of flow over the coastal dunes at Mason Bay, Stewart Island, New Zealand. Simulations building on the complexity of this modeling process are undertaken with a targeted mesh. Included was surface roughness signifying areas of vegetation but no Aeolian sediment transportation. Comparing preliminary results against the existing two and three-dimensional simulations and field data shows that although the strategy of splitting the domain in order to achieve three-dimensional results originally is workable simulating the whole domain is ideal. Grid adaption allows targeting of mesh in areas of most interest, mostly close to the dune surface and within the first 10m above the surface but needs to be done with care. There were distinct differences in wind velocity profile when comparing the results. It is also showed that the model choice has significance for turbulence parameters, with possible implications for sediment transportation, particularly at lower heights. In spite of the complex topography, the flow is strongly two-dimensional in some parts of the domain whilst strongly three dimensional in other areas. Therefore each level of simulation has a role in understanding the underlying flow mechanisms involved and what insight to the flow is required. Understanding gained from the previous work was invaluable in the extension to full three-dimensional simulations.