Analyses of external and global intermittency in the logarithmic layer of Ekman flow
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| Title: | Main Title: Analyses of external and global intermittency in the logarithmic layer of Ekman flow |
| Description: | 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: | 10.1017/jfm.2016.534 (DOI) |
| 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
| Creators: | Cedrick Ansorge (Author), Juan Pedro Mellado (Author) |
| Publisher: | Cambridge University Press |
| Publication Year: | 2017 |
Topic
| TR32 Topic: | Atmosphere |
| Related Subproject: | C7 |
| Subjects: | Keywords: 10m-Wind Speed, 2m-Temperature, Atmospheric Modelling, Atmospheric Stability, Boundary Layer, Multi-Scale |
File Details
| Filename: | jfm_paper.pdf |
| Data Type: | Text - Article |
| File Size: | 3.6 MB |
| Dates: | Issued: 23.09.2016 Accepted: 11.08.2016 |
| Mime Type: | application/pdf |
| Data Format: | |
| Language: | English |
| Status: | Completed |
Constraints
| 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) |
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Specific Information - Publication
| Publication Status: | Published |
| Review Status: | Peer reviewed |
| Publication Type: | Article |
| Article Type: | Journal |
| Source: | Journal of Fluid Mechanics |
| Source Website: | https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/analyses-of-external-and-global-intermittency-in-the-logarithmic-layer-of-ekman-flow/1F177DCB44F9ACFC2F07112482349974 |
| Volume: | 805 |
| Number of Pages: | 25 (611 - 635) |
Metadata Details
| Metadata Creator: | Cedrick Ansorge |
| Metadata Created: | 24.01.2017 |
| Metadata Last Updated: | 24.01.2017 |
| Subproject: | C7 |
| Funding Phase: | 3 |
| Metadata Language: | English |
| Metadata Version: | V50 |
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| Metadata Downloads: | 0 |
| Dataset Downloads: | 7 |
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