Coherent structures in a zero-pressure-gradient and a strongly decelerated boundary layer

Mark P. Simens, Ayse G. Gungor, Yvan Maciel

Research output: Contribution to journalConference articlepeer-review

Abstract

Coherent structures in a strongly decelerated large-velocity-defect turbulent boundary layer (TBL) and a zero pressure gradient (ZPG) boundary layer are analysed by direct numerical simulation (DNS). The characteristics of the one-point velocity stastistics are also considered. The adverse pressure gradient (APG) TBL simulation is a new one carried out by the present authors. The APG TBL begins as a zero pressure gradient boundary layer, decelerates under a strong adverse pressure gradient, and separates near the end of the domain in the form of a very thin separation bubble. The one-point velocity statistics in the outer region of this large-defect boundary layer are compared to those of two other large-velocity-defect APG TBLs (one in dynamic equilibrium, the other in disequilibrium) and a mixing layer. In the upper half of the large-defect boundary layers, the velocity statistics are similar to those of the mixing layer. The dominant peaks of turbulence production and Reynolds stresses are located in the middle of the boundary layers. Three-dimensional spatial correlations of (u, u) and (u, v) show that coherence is lost in the streamwise and spanwise directions as the velocity defect increases. Near-wall streaks tend to disappear in the large-defect zone of the flow to be replaced by more disorganized u motions. Near-wall sweeps and ejections are also less numerous. In the outer region, the u structures tend to be shorter, less streaky, and more inclined with respect to the wall than in the ZPG TBL. The sweeps and ejections are generally bigger with respect to the boundary layer thickness in the large-defect boundary layer, even if the biggest structures are found in the ZPG TBL. Large sweeps and ejections that reach the wall region (wall-attached) are less streamwise elongated and they occupy less space than in the ZPG boundary layer. The distinction between wall-attached and wall-detached structures is not as pronounced in the large-defect TBL.

Original languageEnglish
Article number012013
JournalJournal of Physics: Conference Series
Volume708
Issue number1
DOIs
Publication statusPublished - 29 Apr 2016
Event2nd Multiflow Summer School on Turbulence - Madrid, Spain
Duration: 25 May 201526 Jun 2015

Funding

AGG and YM were supported in part respectively by ITU-BAP and NSERC of Canada. YM thanks TUBITAK (2221 Program) for support 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.

FundersFunder number
ITU-BAP
TUBITAK
Natural Sciences and Engineering Research Council of Canada

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