Structural differences between small and large momentum-defect turbulent boundary layers

Yvan Maciel*, Ayse G. Gungor, Mark Simens

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

We analyse how coherent structures in turbulent boundary layers (TBL) change in response to a strong adverse pressure gradient by using two direct numerical simulation databases. One zone of a zero-pressure-gradient TBL and three zones of a strongly decelerated TBL, corresponding to three ranges of mean velocity defect, with the shape factor varying from 1.54 to 3.75, are considered. We investigate the properties of three-dimensional sweeps, ejections and streamwise-velocity structures. The identified sweeps and ejections contribute everywhere more than 30% to the Reynolds shear stress in both flows. The effect of increasing mean velocity defect in the adverse-pressure-gradient TBL is significant. Streamwise-velocity structures and all wall-attached sweeps and ejections, that is near-wall ones and taller ones that reach the wall region (important in the logarithmic layer of the zero-pressure-gradient TBL), lose their streamwise elongation and become less organised. Wall-attached sweeps and ejections become progressively less numerous and spanwise elongated structures become more frequent. Their strength diminishes in comparison to wall-detached ones and they lose their role as the main contributors to the Reynolds shear stress. In terms of spatial organisation, a pair of side-by-side sweep and ejection is still the dominant configuration, but the probability of such an event has decreased. This fact, together with other results of spatial organisation of structures, does not point toward the presence of a Kelvin-Helmholtz-type instability or a varicose instability of low-speed structures in the outer region, two instabilities that have been suggested in the literature to explain the turbulence regeneration process in large velocity defect turbulent boundary layers.

Original languageEnglish
Pages (from-to)95-110
Number of pages16
JournalInternational Journal of Heat and Fluid Flow
Volume67
DOIs
Publication statusPublished - Oct 2017

Bibliographical note

Publisher Copyright:
© 2017 Elsevier Inc.

Funding

Funded in part by the Multiflow program of the European Research Council. A.G.G. and Y.M. were supported in part respectively by ITU-BAP of Turkey and NSERC of Canada. Y.M. thanks TUBITAK (2221 Program) for supports during the collaboration stay in Turkey. The computations were made possible by generous grants of computer time from Barcelona supercomputing center and from the national center for high performance computing of Turkey (UYBHM) under grant number 1002222012. The authors would like to thank Prof. Jiménez for organizing the First and Second Multiflow Summer Workshops, Juan Sillero and Prof. Jiménez for providing their ZPG TBL data, and Adrián Lozano-Durán and Prof. Jiménez for the processing programs for the Q structures analysis.

FundersFunder number
UYBHM1002222012
Natural Sciences and Engineering Research Council of Canada
European Research Council
Bilimsel Araştırma Projeleri Birimi, İstanbul Teknik Üniversitesi
National Center for High Performance Computing of Turkey

    Keywords

    • Adverse pressure gradient
    • Coherent structures
    • Direct numerical simulation
    • Turbulent boundary layer

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