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The absolute and convective nature of instability in two‐dimensional wakes at low Reynolds numbers

 

作者: Peter A. Monkewitz,  

 

期刊: Physics of Fluids(00319171)  (AIP Available online 1988)
卷期: Volume 31, issue 5  

页码: 999-1006

 

ISSN:0031-9171

 

年代: 1988

 

DOI:10.1063/1.866720

 

出版商: AIP

 

数据来源: AIP

 

摘要:

The linear parallel and incompressible stability of a family of bluff‐body wake profiles is studied at Reynolds numbers close to the onset of Ka´rma´n vortex shedding. The family of mean flow profiles allows for the variation of the wake depth as well as for a variable ratio of wake width to mixing layer thickness. The absolute or convective nature of the sinuous instability is determined as a function of the profile parameters and Reynolds number. A comparison of this survey with experimental data shows that in bluff‐body near wakes a region of local absolute instability begins to form at a Reynolds number of approximately one‐half the critical value for Ka´rma´n vortex shedding. Hence, at the onset of the global response (Ka´rma´n vortex shedding), a substantial region of local absolute instability already exists in the wake. This confirms the qualitative model prediction of Chomaz, Huerre, and Redekopp [submitted to Phys. Rev. Lett.] and also shows that the prediction of vortex shedding frequencies, when based on local stability properties alone, is somewhat arbitrary evenatthe critical Reynolds number.

 

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