NDLI: Components of the spatially-averaged turbulent stress in open channel flows over rough beds

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Components of the spatially-averaged turbulent stress in open channel flows over rough beds

Content Provider	Semantic Scholar
Author	Pokrajac, Dubravka
Copyright Year	2010
Abstract	We investigate spatially heterogeneous open channel flows over rough beds using double averaging methodology. This methodology is based on averaging the fundamental flow equations twice, once in time and once in space. The resulting double-averaged equations can be used as a framework for development of turbulence models. In order to fully explore the potential of such models the stress terms that appear in the momentum equation as a result of each averaging step need to be parameterised. We investigate the stress terms resulting from the double-decomposition of instantaneous velocity. The experimental values of these stress terms were determined from the laboratory experiments involving Particle Image Velocimetry (PIV) measurements of shallow open channel flows over rough beds. The structure of the stress terms and associated turbulent events is investigated using quadrant analysis. For this purpose quadrant analysis is applied either to large-scale or to small-scale velocity fluctuations. The former reveals predominant directions of large turbulent events i.e. of the motion of fluid lumps of size comparable to flow depth. The latter shows the features of small-scale turbulence. The analysis was performed for open channel flows over two types of rough beds: square bars at different spacings and uniform size spheres. It showed that large-scale turbulence in rough wall boundary layers is more anisotropic than the small-scale turbulence. This is a well-known feature, which provides the basis for LES turbulence modelling.
File Format	PDF HTM / HTML
Alternate Webpage(s)	https://izw.baw.de/e-medien/river-flow-2010/PDF/A1/A1_04.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article

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