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  Transition to turbulence in pulsating pipe flow

Xu, D., Warnecke, S., Song, B., Ma, X., & Hof, B. (2017). Transition to turbulence in pulsating pipe flow. Journal of Fluid Mechanics, 831, 418-432. doi:10.1017/jfm.2017.620.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-002E-1501-D Version Permalink: http://hdl.handle.net/21.11116/0000-0001-71D0-4
Genre: Journal Article

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 Creators:
Xu, Duo1, Author              
Warnecke, Sascha2, Author              
Song, B., Author
Ma, X., Author
Hof, Björn1, Author              
Affiliations:
1Max Planck Research Group Complex Dynamics and Turbulence, Max Planck Institute for Dynamics and Self-Organization, Max Planck Society, ou_2063292              
2Emeritus Group Molecular Interactions, Max Planck Institute for Dynamics and Self-Organization, Max Planck Society, ou_2063297              

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Free keywords: instability; transition to turbulence
 Abstract: Fluid flows in nature and applications are frequently subject to periodic velocity modulations. Surprisingly, even for the generic case of flow through a straight pipe, there is little consensus regarding the influence of pulsation on the transition threshold to turbulence: while most studies predict a monotonically increasing threshold with pulsation frequency (i.e. Womersley number, alpha), others observe a decreasing threshold for identical parameters and only observe an increasing threshold at low alpha. In the present study we apply recent advances in the understanding of transition in steady shear flows to pulsating pipe flow. For moderate pulsation amplitudes we find that the first instability encountered is subcritical (i.e. requiring finite amplitude disturbances) and gives rise to localized patches of turbulence ('puffs') analogous to steady pipe flow. By monitoring the impact of pulsation on the lifetime of turbulence we map the onset of turbulence in parameter space. Transition in pulsatile flow can be separated into three regimes. At small Womersley numbers the dynamics is dominated by the decay turbulence suffers during the slower part of the cycle and hence transition is delayed significantly. As shown in this regime thresholds closely agree with estimates based on a quasi-steady flow assumption only taking puff decay rates into account. The transition point predicted in the zero alpha limit equals to the critical point for steady pipe flow offset by the oscillation Reynolds number (i.e. the dimensionless oscillation amplitude). In the high frequency limit on the other hand, puff lifetimes are identical to those in steady pipe flow and hence the transition threshold appears to be unaffected by flow pulsation. In the intermediate frequency regime the transition threshold sharply drops (with increasing alpha) from the decay dominated (quasi-steady) threshold to the steady pipe flow level.

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Language(s): eng - English
 Dates: 2017-10-132017-11-25
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1017/jfm.2017.620
 Degree: -

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Title: Journal of Fluid Mechanics
Source Genre: Journal
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Publ. Info: -
Pages: - Volume / Issue: 831 Sequence Number: - Start / End Page: 418 - 432 Identifier: -