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Periodicity of large-scale coherence in turbulent boundary layers.
- Source :
-
International Journal of Heat & Fluid Flow . Jun2020, Vol. 83, pN.PAG-N.PAG. 1p. - Publication Year :
- 2020
-
Abstract
- This study examines the pronounced periodicity of large-scale coherent structures in turbulent boundary layers, which are of the order of the boundary layer thickness (δ) and reside in the logarithmic and wake regions. To this end, a series of multi-camera planar particle image velocimetry (PIV) measurements are conducted in a streamwise/spanwise and streamwise/wall-normal planes at a friction Reynolds number of Re τ ≈ 2500. The experiments are configured to capture a large field-of-view with velocity fields that cover a streamwise extent in excess of 15 δ. The resulting vector fields reveal large-scale streamwise and spanwise organisation instantaneously, which is often lost when only examining mean statistics. By extracting the dominant streamwise and spanwise Fourier modes of the large-scale motions, a clearer picture of these structural organisations and coherence is presented. A targeted inspection of these dominant modes reveal that these features remain coherent over a significant fraction of the boundary layer thickness in the wall-normal direction, but only a fraction of them have coherence that extends to the wall (wall-coherent). Further, the spatial extents and the population density of these wall-coherent and wall-incoherent modes are characterised, with the former conforming to the attached eddy arguments of Townsend (1976) and the subsequent attached eddy models. Collectively, through the evidence gathered here, we provide a conceptual picture of the representative large-scale structures in turbulent boundary layers, which are likely to have implications on the type of representative structures to be used in structure-based models for these flows. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 0142727X
- Volume :
- 83
- Database :
- Academic Search Index
- Journal :
- International Journal of Heat & Fluid Flow
- Publication Type :
- Academic Journal
- Accession number :
- 143234226
- Full Text :
- https://doi.org/10.1016/j.ijheatfluidflow.2020.108575