Skewness and flatness factors of the longitudinal velocity derivative in wall-bounded flows

Skewness and flatness factors of the longitudinal velocity derivative in wall-bounded flows Hot-wire measurements are carried out in turbulent boundary layers over smooth and rough walls in order the assess the behavior of the skewness (S) and flatness (F) factors of the longitudinal velocity derivative as y, the distance from the wall, increases. The measurements are complemented by direct numerical simulations of a smooth wall turbulent channel flow. It is observed that, as the distance to the wall increases, S and F vary significantly before approaching a constant in the outer layer of the boundary layer. Further, S and F exhibit a nontrivial dependence on the Taylor microscale Reynolds number (Reλ). For example, in the region below about 0.2δ (δ is the boundary layer thickness) where Reλ varies significantly, S and F strongly vary with Reλ and can be multivalued at a given Reλ. In the outer region, between 0.3δ and 0.6δ, S, F, and Reλ remain approximately constant. The channel flow direct numerical simulation data for S and F exhibit a similar behavior. These results point to the ambiguity that can arise when assessing the Reλ dependence of S and F in wall shear flows. In particular, the multivaluedness of S and F can lead to erroneous conclusions if y/δ is known only poorly, as is the case for the atmospheric shear layer (ASL). If the laboratory turbulent boundary layer is considered an adequate surrogate to the neutral ASL, then the behavior of S and F in the ASL is expected to be similar to that reported here. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review Fluids American Physical Society (APS)

Skewness and flatness factors of the longitudinal velocity derivative in wall-bounded flows

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Skewness and flatness factors of the longitudinal velocity derivative in wall-bounded flows

Abstract

Hot-wire measurements are carried out in turbulent boundary layers over smooth and rough walls in order the assess the behavior of the skewness (S) and flatness (F) factors of the longitudinal velocity derivative as y, the distance from the wall, increases. The measurements are complemented by direct numerical simulations of a smooth wall turbulent channel flow. It is observed that, as the distance to the wall increases, S and F vary significantly before approaching a constant in the outer layer of the boundary layer. Further, S and F exhibit a nontrivial dependence on the Taylor microscale Reynolds number (Reλ). For example, in the region below about 0.2δ (δ is the boundary layer thickness) where Reλ varies significantly, S and F strongly vary with Reλ and can be multivalued at a given Reλ. In the outer region, between 0.3δ and 0.6δ, S, F, and Reλ remain approximately constant. The channel flow direct numerical simulation data for S and F exhibit a similar behavior. These results point to the ambiguity that can arise when assessing the Reλ dependence of S and F in wall shear flows. In particular, the multivaluedness of S and F can lead to erroneous conclusions if y/δ is known only poorly, as is the case for the atmospheric shear layer (ASL). If the laboratory turbulent boundary layer is considered an adequate surrogate to the neutral ASL, then the behavior of S and F in the ASL is expected to be similar to that reported here.
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Publisher
The American Physical Society
Copyright
Copyright © ©2017 American Physical Society
eISSN
2469-990X
D.O.I.
10.1103/PhysRevFluids.2.064608
Publisher site
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Abstract

Hot-wire measurements are carried out in turbulent boundary layers over smooth and rough walls in order the assess the behavior of the skewness (S) and flatness (F) factors of the longitudinal velocity derivative as y, the distance from the wall, increases. The measurements are complemented by direct numerical simulations of a smooth wall turbulent channel flow. It is observed that, as the distance to the wall increases, S and F vary significantly before approaching a constant in the outer layer of the boundary layer. Further, S and F exhibit a nontrivial dependence on the Taylor microscale Reynolds number (Reλ). For example, in the region below about 0.2δ (δ is the boundary layer thickness) where Reλ varies significantly, S and F strongly vary with Reλ and can be multivalued at a given Reλ. In the outer region, between 0.3δ and 0.6δ, S, F, and Reλ remain approximately constant. The channel flow direct numerical simulation data for S and F exhibit a similar behavior. These results point to the ambiguity that can arise when assessing the Reλ dependence of S and F in wall shear flows. In particular, the multivaluedness of S and F can lead to erroneous conclusions if y/δ is known only poorly, as is the case for the atmospheric shear layer (ASL). If the laboratory turbulent boundary layer is considered an adequate surrogate to the neutral ASL, then the behavior of S and F in the ASL is expected to be similar to that reported here.

Journal

Physical Review FluidsAmerican Physical Society (APS)

Published: Jun 28, 2017

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