[1580] - Analyses of external and global intermittency in the logarithmic layer of Ekman flow

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Ansorge, C., Mellado, J. P., 2016. Analyses of external and global intermittency in the logarithmic layer of Ekman flow. Journal of Fluid Mechanics, 805, 611 - 635. DOI: 10.1017/jfm.2016.534.
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Title(s):Main Title: Analyses of external and global intermittency in the logarithmic layer of Ekman flow
Description(s):Abstract: Existence of non-turbulent flow patches in the vicinity of the wall of a turbulent flow is known as global intermittency. Global intermittency challenges the conventional statistics approach when describing turbulence in the inner layer and calls for the use of conditional statistics. We extend the vorticity-based conditioning of a flow to turbulent and non-turbulent sub-volumes by a high-pass filter operation. This modified method consistently detects non-turbulent flow patches in the outer and inner layers for stratifications ranging from the neutral limit to extreme stability, where the flow is close to a complete laminarization. When applying this conditioning method to direct numerical simulation data of stably stratified Ekman flow, we find the following. First, external intermittency has a strong effect on the logarithmic law for the mean velocity in Ekman flow under neutral stratification. If instead of the full field, only turbulent sub-volumes are considered, the data fit an idealized logarithmic velocity profile much better; in particular, a problematic dip in the von Kármán measure κ in the surface layer is decreased by approximately 50 % and our data only support the reduced range 0.41≲κ≲0.43. Second, order-one changes in turbulent quantities under strong stratification can be explained by a modulation of the turbulent volume fraction rather than by a structural change of individual turbulence events; within the turbulent fraction of the flow, the character of individual turbulence events measured in terms of turbulence dissipation rate or variance of velocity fluctuations is similar to that under neutral stratification.
Identifier(s):DOI: 10.1017/jfm.2016.534
Citation Advice:Ansorge, C. and Mellado, J.P. (2016) ‘Analyses of external and global intermittency in the logarithmic layer of Ekman flow’, Journal of Fluid Mechanics, 805, pp. 611–635. doi: 10.1017/jfm.2016.534.
Responsible Party
Creator(s):Author: Cedrick Ansorge
Author: Juan Pedro Mellado
Publisher:Cambridge University Press
TR32 Topic:Atmosphere
Related Sub-project(s):C7
Subject(s):CRC/TR32 Keywords: 10m-Wind Speed, 2m-Temperature, Atmospheric Modelling, Atmospheric Stability, Boundary Layer, Multi-Scale
File Details
File Name:jfm_paper.pdf
Data Type:Text
File Size:3725 kB (3.638 MB)
Date(s):Issued: 2016-09-23
Date Accepted: 2016-08-11
Mime Type:application/pdf
Data Format:PDF
Download Permission:Free
General Access and Use Conditions:According to the TR32DB data policy agreement.
Access Limitations:According to the TR32DB data policy agreement.
Licence:Creative Commons Attribution 4.0 International (CC BY 4.0)
North:-no map data
Measurement Region:Laboratory
Measurement Location:--Laboratory--
Specific Informations - Publication
Article Type:Journal
Source:Journal of Fluid Mechanics
Number Of Pages:25
Page Range:611 - 635
Metadata Details
Metadata Creator:Cedrick Ansorge
Metadata Created:2017-01-24
Metadata Last Updated:2017-01-24
Funding Phase:3
Metadata Language:English
Metadata Version:V41
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