Niels Ulrik Sørensen

Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain

The use of Large-Eddy Simulation (LES) to predict wall-bounded flows has presently been limited to low Reynolds number flows. Since the number of computational grid points required to resolve the near-wall turbulent structures increase rapidly with Reynolds number, LES has been unattainable for flows at high Reynolds numbers. To reduce the computational cost of traditional LES a hybrid method is proposed in which the near-wall eddies are modelled in a Reynolds-averaged sense. Close to walls the flow is treated with the RANS-equations and this layer act as wall model for the outer flow handled by LES. The well-known high Reynolds number two-equation k - turbulence model is used in the RANS layer and the model automatically switches to a two-equation k - subgrid-scale stress model in the LES region. The approach can be used for flow over rough walls. To demonstrate the ability of the proposed hybrid method, simulations of the wind flow over a complex terrain near Wellington in New Zealand are presented. Under certain conditions unsteady flow features have been measured at the site - flow features that could lead to high structural loads on a planned wind farm. These transient flow phenomena are reproduced with the new RANS/LES method. Additionally, the results from the hybrid method are compared with pure RANS results.

Living on the Periphery of Youth: Young People’s Narratives of Youth Life in Rural Areas

Drawing on theoretical perspectives regarding the importance of place and belonging to a place in understanding young people’s lives as well as broader processes of social change and continuity, this article explores conceptions of youth as experienced—and narrated—by young people living in rural areas. The article analyzes how discourses on urbanism and youth can be traced in young people’s narratives about their communities and their own lives as young people; how these discourses seem to frame the young people’s narratives and how they rearticulate these discourses through their accounts (Davies, 2000). In the article, we thus also focus attention on the cracks and opposing discourses that can be identified in the young people’s narratives, and how they influence their relationship with their local area.