The final stages of transition and the reattachment region in transitional separation bubbles

The final stages of transition and the reattachment region in transitional separation bubbles The final stages of transitional phenomena in laminar separation bubbles play a key role in their reattachment process, and they condition the boundary layer properties and flow structure after reattachment. In this experimental study, the evolution of the perturbation velocity spectra found in this zone is first presented, showing the nonlinear growth of instabilities in their path to develop fully turbulent spectra. The study of the average flow field allows the scaling of the reattachment region, both in its extension and in the characterization of the integral boundary layer magnitudes. Experimental laws are proposed for the evolution of the momentum thickness and of the shape factor. In addition, a universal, wake-like mean velocity profile is found shortly after the reattachment station. The phase-locked characterization technique allows measurements conditioned to the presence of a fluid event. This technique is used to track the evolution of large-scale structures, whose dynamics is seen to dominate the fluid behavior in the reattachment zone. The simultaneous existence of two vortex blobs is found to characterize this flow region, with the longest lived one being convected toward the wall and stretched. This process results in the fast breakdown of the large-scale vorticity structure and the sudden formation of 3-D, small scales that promote the rapid flow evolution toward a fully developed turbulent state. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

The final stages of transition and the reattachment region in transitional separation bubbles

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Publisher
Springer Journals
Copyright
Copyright © 2014 by Springer-Verlag Berlin Heidelberg
Subject
Engineering; Engineering Fluid Dynamics; Fluid- and Aerodynamics; Engineering Thermodynamics, Heat and Mass Transfer
ISSN
0723-4864
eISSN
1432-1114
D.O.I.
10.1007/s00348-014-1695-7
Publisher site
See Article on Publisher Site

Abstract

The final stages of transitional phenomena in laminar separation bubbles play a key role in their reattachment process, and they condition the boundary layer properties and flow structure after reattachment. In this experimental study, the evolution of the perturbation velocity spectra found in this zone is first presented, showing the nonlinear growth of instabilities in their path to develop fully turbulent spectra. The study of the average flow field allows the scaling of the reattachment region, both in its extension and in the characterization of the integral boundary layer magnitudes. Experimental laws are proposed for the evolution of the momentum thickness and of the shape factor. In addition, a universal, wake-like mean velocity profile is found shortly after the reattachment station. The phase-locked characterization technique allows measurements conditioned to the presence of a fluid event. This technique is used to track the evolution of large-scale structures, whose dynamics is seen to dominate the fluid behavior in the reattachment zone. The simultaneous existence of two vortex blobs is found to characterize this flow region, with the longest lived one being convected toward the wall and stretched. This process results in the fast breakdown of the large-scale vorticity structure and the sudden formation of 3-D, small scales that promote the rapid flow evolution toward a fully developed turbulent state.

Journal

Experiments in FluidsSpringer Journals

Published: Mar 22, 2014

References

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